From e1aa949a764f55b78667d3d5362cc7e92e1ff12f Mon Sep 17 00:00:00 2001
From: Yoseph Maguire <yoseph.maguire@microsoft.com>
Date: Mon, 20 Dec 2021 23:45:07 -0600
Subject: [PATCH] chore: var to let/const and audit dev dependencies (#1374)

* fix: audit dev dependencies

* add changes

* timeout

* add timeout

* remove aftereach

* fixes
---
 README.md                                 |  20 +-
 benchmarks/bombing.js                     |   8 +-
 benchmarks/throughputCounter.js           |   8 +-
 bin/mqtt.js                               |   6 +-
 bin/pub.js                                |  24 +-
 bin/sub.js                                |  12 +-
 example.js                                |   4 +-
 examples/client/secure-client.js          |  16 +-
 examples/client/simple-both.js            |   6 +-
 examples/client/simple-publish.js         |   4 +-
 examples/client/simple-subscribe.js       |   4 +-
 examples/tls client/mqttclient.js         |  20 +-
 examples/ws/client.js                     |  10 +-
 examples/wss/client_with_proxy.js         |  24 +-
 lib/client.js                             | 308 +++++----
 lib/connect/ali.js                        |  28 +-
 lib/connect/index.js                      |  21 +-
 lib/connect/tcp.js                        |   9 +-
 lib/connect/tls.js                        |  11 +-
 lib/connect/ws.js                         |  28 +-
 lib/connect/wx.js                         |  24 +-
 lib/default-message-id-provider.js        |   2 +-
 lib/store.js                              |  18 +-
 lib/topic-alias-send.js                   |   6 +-
 lib/unique-message-id-provider.js         |   2 +-
 lib/validations.js                        |   6 +-
 mqtt.js                                   |  10 +-
 package.json                              |  19 +-
 test/abstract_client.js                   | 807 +++++++++++-----------
 test/abstract_store.js                    |  19 +-
 test/browser/server.js                    |  43 +-
 test/browser/test.js                      |  24 +-
 test/client.js                            | 116 ++--
 test/client_mqtt5.js                      | 244 +++----
 test/helpers/port_list.js                 |  48 +-
 test/helpers/server.js                    |  18 +-
 test/helpers/server_process.js            |   2 +-
 test/message-id-provider.js               |  33 +-
 test/mqtt.js                              |  57 +-
 test/mqtt_store.js                        |   2 +-
 test/secure_client.js                     |  47 +-
 test/server.js                            |  20 +-
 test/server_helpers_for_client_tests.js   |  86 +--
 test/store.js                             |   4 +-
 test/unique_message_id_provider_client.js |  12 +-
 test/util.js                              |   4 +-
 test/websocket_client.js                  |  63 +-
 47 files changed, 1173 insertions(+), 1134 deletions(-)

diff --git a/README.md b/README.md
index 5c0570c48..1ac0970c8 100644
--- a/README.md
+++ b/README.md
@@ -83,8 +83,8 @@ npm install mqtt --save
 For the sake of simplicity, let's put the subscriber and the publisher in the same file:
 
 ```js
-var mqtt = require('mqtt')
-var client  = mqtt.connect('mqtt://test.mosquitto.org')
+const mqtt = require('mqtt')
+const client  = mqtt.connect('mqtt://test.mosquitto.org')
 
 client.on('connect', function () {
   client.subscribe('presence', function (err) {
@@ -121,8 +121,8 @@ to use MQTT.js in the browser see the [browserify](#browserify) section
 ## Import styles
 ### CommonJS (Require)
 ```js
-var mqtt = require('mqtt')  // require mqtt
-var client = mqtt.connect('est.mosquitto.org')  // create a client
+const mqtt = require('mqtt')  // require mqtt
+const client = mqtt.connect('est.mosquitto.org')  // create a client
 ```
 ### ES6 Modules (Import)
 #### Aliased wildcard import
@@ -695,7 +695,7 @@ gzip <browserMqtt.js | wc -c
 <a name="webpack"></a>
 ### Webpack
 
-Just like browserify, export MQTT.js as library. The exported module would be `var mqtt = xxx` and it will add an object in the global space. You could also export module in other [formats (AMD/CommonJS/others)](http://webpack.github.io/docs/configuration.html#output-librarytarget) by setting **output.libraryTarget** in webpack configuration.
+Just like browserify, export MQTT.js as library. The exported module would be `const mqtt = xxx` and it will add an object in the global space. You could also export module in other [formats (AMD/CommonJS/others)](http://webpack.github.io/docs/configuration.html#output-librarytarget) by setting **output.libraryTarget** in webpack configuration.
 
 ```javascript
 npm install -g webpack // install webpack
@@ -715,7 +715,7 @@ you can then use mqtt.js in the browser with the same api than node's one.
 <body>
 <script src="./browserMqtt.js"></script>
 <script>
-  var client = mqtt.connect() // you add a ws:// url here
+  const client = mqtt.connect() // you add a ws:// url here
   client.subscribe("mqtt/demo")
 
   client.on("message", function (topic, payload) {
@@ -803,8 +803,8 @@ let client : mqtt.MqttClient = mqtt.connect('mqtt://test.mosquitto.org')
 Supports [WeChat Mini Program](https://mp.weixin.qq.com/). Use the `wxs` protocol. See [the WeChat docs](https://mp.weixin.qq.com/debug/wxadoc/dev/api/network-socket.html).
 
 ```js
-var mqtt = require('mqtt')
-var client = mqtt.connect('wxs://test.mosquitto.org')
+const mqtt = require('mqtt')
+const client = mqtt.connect('wxs://test.mosquitto.org')
 ```
 
 ### Ali Mini Program
@@ -812,8 +812,8 @@ Supports [Ali Mini Program](https://open.alipay.com/channel/miniIndex.htm). Use
 <a name="example"></a>
 
 ```js
-var mqtt = require('mqtt')
-var client = mqtt.connect('alis://test.mosquitto.org')
+const mqtt = require('mqtt')
+const client = mqtt.connect('alis://test.mosquitto.org')
 ```
 
 <a name="contributing"></a>
diff --git a/benchmarks/bombing.js b/benchmarks/bombing.js
index adef01445..4d158c2b4 100755
--- a/benchmarks/bombing.js
+++ b/benchmarks/bombing.js
@@ -1,10 +1,10 @@
 #! /usr/bin/env node
 
-var mqtt = require('../')
-var client = mqtt.connect({ port: 1883, host: 'localhost', clean: true, keepalive: 0 })
+const mqtt = require('../')
+const client = mqtt.connect({ port: 1883, host: 'localhost', clean: true, keepalive: 0 })
 
-var sent = 0
-var interval = 5000
+let sent = 0
+const interval = 5000
 
 function count () {
   console.log('sent/s', sent / interval * 1000)
diff --git a/benchmarks/throughputCounter.js b/benchmarks/throughputCounter.js
index 0b778ef2c..c2dbabfc5 100755
--- a/benchmarks/throughputCounter.js
+++ b/benchmarks/throughputCounter.js
@@ -1,10 +1,10 @@
 #! /usr/bin/env node
 
-var mqtt = require('../')
+const mqtt = require('../')
 
-var client = mqtt.connect({ port: 1883, host: 'localhost', clean: true, encoding: 'binary', keepalive: 0 })
-var counter = 0
-var interval = 5000
+const client = mqtt.connect({ port: 1883, host: 'localhost', clean: true, encoding: 'binary', keepalive: 0 })
+let counter = 0
+const interval = 5000
 
 function count () {
   console.log('received/s', counter / interval * 1000)
diff --git a/bin/mqtt.js b/bin/mqtt.js
index 022b33a64..edba1609d 100755
--- a/bin/mqtt.js
+++ b/bin/mqtt.js
@@ -7,9 +7,9 @@
  *
  * See LICENSE for more information
  */
-var path = require('path')
-var commist = require('commist')()
-var helpMe = require('help-me')({
+const path = require('path')
+const commist = require('commist')()
+const helpMe = require('help-me')({
   dir: path.join(path.dirname(require.main.filename), '/../doc'),
   ext: '.txt'
 })
diff --git a/bin/pub.js b/bin/pub.js
index 94b066b40..2ea11f747 100755
--- a/bin/pub.js
+++ b/bin/pub.js
@@ -2,20 +2,20 @@
 
 'use strict'
 
-var mqtt = require('../')
-var pump = require('pump')
-var path = require('path')
-var fs = require('fs')
-var concat = require('concat-stream')
-var Writable = require('readable-stream').Writable
-var helpMe = require('help-me')({
+const mqtt = require('../')
+const pump = require('pump')
+const path = require('path')
+const fs = require('fs')
+const concat = require('concat-stream')
+const Writable = require('readable-stream').Writable
+const helpMe = require('help-me')({
   dir: path.join(__dirname, '..', 'doc')
 })
-var minimist = require('minimist')
-var split2 = require('split2')
+const minimist = require('minimist')
+const split2 = require('split2')
 
 function send (args) {
-  var client = mqtt.connect(args)
+  const client = mqtt.connect(args)
   client.on('connect', function () {
     client.publish(args.topic, args.message, args, function (err) {
       if (err) {
@@ -31,8 +31,8 @@ function send (args) {
 }
 
 function multisend (args) {
-  var client = mqtt.connect(args)
-  var sender = new Writable({
+  const client = mqtt.connect(args)
+  const sender = new Writable({
     objectMode: true
   })
   sender._write = function (line, enc, cb) {
diff --git a/bin/sub.js b/bin/sub.js
index 14bc57458..cb113a779 100755
--- a/bin/sub.js
+++ b/bin/sub.js
@@ -1,12 +1,12 @@
 #!/usr/bin/env node
 
-var mqtt = require('../')
-var path = require('path')
-var fs = require('fs')
-var helpMe = require('help-me')({
+const mqtt = require('../')
+const path = require('path')
+const fs = require('fs')
+const helpMe = require('help-me')({
   dir: path.join(__dirname, '..', 'doc')
 })
-var minimist = require('minimist')
+const minimist = require('minimist')
 
 function start (args) {
   args = minimist(args, {
@@ -84,7 +84,7 @@ function start (args) {
 
   args.keepAlive = args['keep-alive']
 
-  var client = mqtt.connect(args)
+  const client = mqtt.connect(args)
 
   client.on('connect', function () {
     client.subscribe(args.topic, { qos: args.qos }, function (err, result) {
diff --git a/example.js b/example.js
index ba14bf949..c5c8568a2 100644
--- a/example.js
+++ b/example.js
@@ -1,5 +1,5 @@
-var mqtt = require('./')
-var client = mqtt.connect('mqtt://test.mosquitto.org')
+const mqtt = require('./')
+const client = mqtt.connect('mqtt://test.mosquitto.org')
 
 client.subscribe('presence')
 client.publish('presence', 'Hello mqtt')
diff --git a/examples/client/secure-client.js b/examples/client/secure-client.js
index bf9b6f092..20d28132a 100644
--- a/examples/client/secure-client.js
+++ b/examples/client/secure-client.js
@@ -1,21 +1,21 @@
 'use strict'
 
-var mqtt = require('../..')
-var path = require('path')
-var fs = require('fs')
-var KEY = fs.readFileSync(path.join(__dirname, '..', '..', 'test', 'helpers', 'tls-key.pem'))
-var CERT = fs.readFileSync(path.join(__dirname, '..', '..', 'test', 'helpers', 'tls-cert.pem'))
+const mqtt = require('../..')
+const path = require('path')
+const fs = require('fs')
+const KEY = fs.readFileSync(path.join(__dirname, '..', '..', 'test', 'helpers', 'tls-key.pem'))
+const CERT = fs.readFileSync(path.join(__dirname, '..', '..', 'test', 'helpers', 'tls-cert.pem'))
 
-var PORT = 8443
+const PORT = 8443
 
-var options = {
+const options = {
   port: PORT,
   key: KEY,
   cert: CERT,
   rejectUnauthorized: false
 }
 
-var client = mqtt.connect(options)
+const client = mqtt.connect(options)
 
 client.subscribe('messages')
 client.publish('messages', 'Current time is: ' + new Date())
diff --git a/examples/client/simple-both.js b/examples/client/simple-both.js
index 8e9268b5f..29708fb74 100644
--- a/examples/client/simple-both.js
+++ b/examples/client/simple-both.js
@@ -1,9 +1,9 @@
 'use strict'
 
-var mqtt = require('../..')
-var client = mqtt.connect()
+const mqtt = require('../..')
+const client = mqtt.connect()
 
-// or var client = mqtt.connect({ port: 1883, host: '192.168.1.100', keepalive: 10000});
+// or const client = mqtt.connect({ port: 1883, host: '192.168.1.100', keepalive: 10000});
 
 client.subscribe('presence')
 client.publish('presence', 'bin hier')
diff --git a/examples/client/simple-publish.js b/examples/client/simple-publish.js
index a8b0f89b6..24d232cb6 100644
--- a/examples/client/simple-publish.js
+++ b/examples/client/simple-publish.js
@@ -1,7 +1,7 @@
 'use strict'
 
-var mqtt = require('../..')
-var client = mqtt.connect()
+const mqtt = require('../..')
+const client = mqtt.connect()
 
 client.publish('presence', 'hello!')
 client.end()
diff --git a/examples/client/simple-subscribe.js b/examples/client/simple-subscribe.js
index 7989b9c22..b12ecbe38 100644
--- a/examples/client/simple-subscribe.js
+++ b/examples/client/simple-subscribe.js
@@ -1,7 +1,7 @@
 'use strict'
 
-var mqtt = require('../..')
-var client = mqtt.connect()
+const mqtt = require('../..')
+const client = mqtt.connect()
 
 client.subscribe('presence')
 client.on('message', function (topic, message) {
diff --git a/examples/tls client/mqttclient.js b/examples/tls client/mqttclient.js
index 392fcb39c..dff75d725 100644
--- a/examples/tls client/mqttclient.js	
+++ b/examples/tls client/mqttclient.js	
@@ -14,17 +14,17 @@
   <the ip address of the server> stark
  *******************************************************************************/
 
-var mqtt = require('mqtt')
-var fs = require('fs')
-var path = require('path')
-var KEY = fs.readFileSync(path.join(__dirname, '/tls-key.pem'))
-var CERT = fs.readFileSync(path.join(__dirname, '/tls-cert.pem'))
-var TRUSTED_CA_LIST = fs.readFileSync(path.join(__dirname, '/crt.ca.cg.pem'))
+const mqtt = require('mqtt')
+const fs = require('fs')
+const path = require('path')
+const KEY = fs.readFileSync(path.join(__dirname, '/tls-key.pem'))
+const CERT = fs.readFileSync(path.join(__dirname, '/tls-cert.pem'))
+const TRUSTED_CA_LIST = fs.readFileSync(path.join(__dirname, '/crt.ca.cg.pem'))
 
-var PORT = 1883
-var HOST = 'stark'
+const PORT = 1883
+const HOST = 'stark'
 
-var options = {
+const options = {
   port: PORT,
   host: HOST,
   key: KEY,
@@ -35,7 +35,7 @@ var options = {
   protocol: 'mqtts'
 }
 
-var client = mqtt.connect(options)
+const client = mqtt.connect(options)
 
 client.subscribe('messages')
 client.publish('messages', 'Current time is: ' + new Date())
diff --git a/examples/ws/client.js b/examples/ws/client.js
index 61524d345..7f44e903c 100644
--- a/examples/ws/client.js
+++ b/examples/ws/client.js
@@ -1,8 +1,8 @@
 'use strict'
 
-var mqtt = require('../../')
+const mqtt = require('../../')
 
-var clientId = 'mqttjs_' + Math.random().toString(16).substr(2, 8)
+const clientId = 'mqttjs_' + Math.random().toString(16).substr(2, 8)
 
 // This sample should be run in tandem with the aedes_server.js file.
 // Simply run it:
@@ -11,9 +11,9 @@ var clientId = 'mqttjs_' + Math.random().toString(16).substr(2, 8)
 // Then run this file in a separate console:
 // $ node websocket_sample.js
 //
-var host = 'ws://localhost:8080'
+const host = 'ws://localhost:8080'
 
-var options = {
+const options = {
   keepalive: 30,
   clientId: clientId,
   protocolId: 'MQTT',
@@ -31,7 +31,7 @@ var options = {
 }
 
 console.log('connecting mqtt client')
-var client = mqtt.connect(host, options)
+const client = mqtt.connect(host, options)
 
 client.on('error', function (err) {
   console.log(err)
diff --git a/examples/wss/client_with_proxy.js b/examples/wss/client_with_proxy.js
index 4a0d9f3c9..f0a9ea0c9 100644
--- a/examples/wss/client_with_proxy.js
+++ b/examples/wss/client_with_proxy.js
@@ -1,29 +1,31 @@
 'use strict'
 
-var mqtt = require('mqtt')
-var url = require('url')
-var HttpsProxyAgent = require('https-proxy-agent')
+const mqtt = require('mqtt')
+const url = require('url')
+const HttpsProxyAgent = require('https-proxy-agent')
 /*
 host: host of the endpoint you want to connect e.g. my.mqqt.host.com
 path: path to you endpoint e.g. '/foo/bar/mqtt'
 */
-var endpoint = 'wss://<host><path>'
+const endpoint = 'wss://<host><path>'
 /* create proxy agent
 proxy: your proxy e.g. proxy.foo.bar.com
 port: http proxy port e.g. 8080
 */
-var proxy = process.env.http_proxy || 'http://<proxy>:<port>'
-var parsed = url.parse(endpoint)
-var proxyOpts = url.parse(proxy)
+const proxy = process.env.http_proxy || 'http://<proxy>:<port>'
+// eslint-disable-next-line
+const parsed = url.parse(endpoint)
+// eslint-disable-next-line
+const proxyOpts = url.parse(proxy)
 // true for wss
 proxyOpts.secureEndpoint = parsed.protocol ? parsed.protocol === 'wss:' : true
-var agent = new HttpsProxyAgent(proxyOpts)
-var wsOptions = {
+const agent = new HttpsProxyAgent(proxyOpts)
+const wsOptions = {
   agent: agent
   // other wsOptions
   // foo:'bar'
 }
-var mqttOptions = {
+const mqttOptions = {
   keepalive: 60,
   reschedulePings: true,
   protocolId: 'MQTT',
@@ -35,7 +37,7 @@ var mqttOptions = {
   wsOptions: wsOptions
 }
 
-var client = mqtt.connect(parsed, mqttOptions)
+const client = mqtt.connect(parsed, mqttOptions)
 
 client.on('connect', function () {
   console.log('connected')
diff --git a/lib/client.js b/lib/client.js
index 540a11780..d4bd093b2 100644
--- a/lib/client.js
+++ b/lib/client.js
@@ -3,25 +3,25 @@
 /**
  * Module dependencies
  */
-var EventEmitter = require('events').EventEmitter
-var Store = require('./store')
-var TopicAliasRecv = require('./topic-alias-recv')
-var TopicAliasSend = require('./topic-alias-send')
-var mqttPacket = require('mqtt-packet')
-var DefaultMessageIdProvider = require('./default-message-id-provider')
-var Writable = require('readable-stream').Writable
-var inherits = require('inherits')
-var reInterval = require('reinterval')
-var clone = require('rfdc/default')
-var validations = require('./validations')
-var xtend = require('xtend')
-var debug = require('debug')('mqttjs:client')
-var nextTick = process ? process.nextTick : function (callback) { setTimeout(callback, 0) }
-var setImmediate = global.setImmediate || function (callback) {
+const EventEmitter = require('events').EventEmitter
+const Store = require('./store')
+const TopicAliasRecv = require('./topic-alias-recv')
+const TopicAliasSend = require('./topic-alias-send')
+const mqttPacket = require('mqtt-packet')
+const DefaultMessageIdProvider = require('./default-message-id-provider')
+const Writable = require('readable-stream').Writable
+const inherits = require('inherits')
+const reInterval = require('reinterval')
+const clone = require('rfdc/default')
+const validations = require('./validations')
+const xtend = require('xtend')
+const debug = require('debug')('mqttjs:client')
+const nextTick = process ? process.nextTick : function (callback) { setTimeout(callback, 0) }
+const setImmediate = global.setImmediate || function (callback) {
   // works in node v0.8
   nextTick(callback)
 }
-var defaultConnectOptions = {
+const defaultConnectOptions = {
   keepalive: 60,
   reschedulePings: true,
   protocolId: 'MQTT',
@@ -32,7 +32,7 @@ var defaultConnectOptions = {
   resubscribe: true
 }
 
-var socketErrors = [
+const socketErrors = [
   'ECONNREFUSED',
   'EADDRINUSE',
   'ECONNRESET',
@@ -41,7 +41,7 @@ var socketErrors = [
 
 // Other Socket Errors: EADDRINUSE, ECONNRESET, ENOTFOUND.
 
-var errors = {
+const errors = {
   0: '',
   1: 'Unacceptable protocol version',
   2: 'Identifier rejected',
@@ -94,11 +94,11 @@ function defaultId () {
 function applyTopicAlias (client, packet) {
   if (client.options.protocolVersion === 5) {
     if (packet.cmd === 'publish') {
-      var alias
+      let alias
       if (packet.properties) {
         alias = packet.properties.topicAlias
       }
-      var topic = packet.topic.toString()
+      const topic = packet.topic.toString()
       if (client.topicAliasSend) {
         if (alias) {
           if (topic.length !== 0) {
@@ -115,19 +115,19 @@ function applyTopicAlias (client, packet) {
               alias = client.topicAliasSend.getAliasByTopic(topic)
               if (alias) {
                 packet.topic = ''
-                packet.properties = {...(packet.properties), topicAlias: alias}
+                packet.properties = { ...(packet.properties), topicAlias: alias }
                 debug('applyTopicAlias :: auto assign(use) topic: %s - alias: %d', topic, alias)
               } else {
                 alias = client.topicAliasSend.getLruAlias()
                 client.topicAliasSend.put(topic, alias)
-                packet.properties = {...(packet.properties), topicAlias: alias}
+                packet.properties = { ...(packet.properties), topicAlias: alias }
                 debug('applyTopicAlias :: auto assign topic: %s - alias: %d', topic, alias)
               }
             } else if (client.options.autoUseTopicAlias) {
               alias = client.topicAliasSend.getAliasByTopic(topic)
               if (alias) {
                 packet.topic = ''
-                packet.properties = {...(packet.properties), topicAlias: alias}
+                packet.properties = { ...(packet.properties), topicAlias: alias }
                 debug('applyTopicAlias :: auto use topic: %s - alias: %d', topic, alias)
               }
             }
@@ -142,12 +142,12 @@ function applyTopicAlias (client, packet) {
 }
 
 function removeTopicAliasAndRecoverTopicName (client, packet) {
-  var alias
+  let alias
   if (packet.properties) {
     alias = packet.properties.topicAlias
   }
 
-  var topic = packet.topic.toString()
+  let topic = packet.topic.toString()
   if (topic.length === 0) {
     // restore topic from alias
     if (typeof alias === 'undefined') {
@@ -173,7 +173,7 @@ function sendPacket (client, packet, cb) {
   client.emit('packetsend', packet)
 
   debug('sendPacket :: writing to stream')
-  var result = mqttPacket.writeToStream(packet, client.stream, client.options)
+  const result = mqttPacket.writeToStream(packet, client.stream, client.options)
   debug('sendPacket :: writeToStream result %s', result)
   if (!result && cb) {
     debug('sendPacket :: handle events on `drain` once through callback.')
@@ -210,8 +210,8 @@ function flushVolatile (queue) {
 
 function storeAndSend (client, packet, cb, cbStorePut) {
   debug('storeAndSend :: store packet with cmd %s to outgoingStore', packet.cmd)
-  var storePacket = packet
-  var err
+  let storePacket = packet
+  let err
   if (storePacket.cmd === 'publish') {
     // The original packet is for sending.
     // The cloned storePacket is for storing to resend on reconnect.
@@ -243,8 +243,8 @@ function nop (error) {
  * (see Connection#connect)
  */
 function MqttClient (streamBuilder, options) {
-  var k
-  var that = this
+  let k
+  const that = this
 
   if (!(this instanceof MqttClient)) {
     return new MqttClient(streamBuilder, options)
@@ -327,12 +327,12 @@ function MqttClient (streamBuilder, options) {
 
   // Send queued packets
   this.on('connect', function () {
-    var queue = this.queue
+    const queue = this.queue
 
     function deliver () {
-      var entry = queue.shift()
+      const entry = queue.shift()
       debug('deliver :: entry %o', entry)
-      var packet = null
+      let packet = null
 
       if (!entry) {
         that._resubscribe()
@@ -341,7 +341,7 @@ function MqttClient (streamBuilder, options) {
 
       packet = entry.packet
       debug('deliver :: call _sendPacket for %o', packet)
-      var send = true
+      let send = true
       if (packet.messageId && packet.messageId !== 0) {
         if (!that.messageIdProvider.register(packet.messageId)) {
           send = false
@@ -400,12 +400,11 @@ inherits(MqttClient, EventEmitter)
  * @api private
  */
 MqttClient.prototype._setupStream = function () {
-  var connectPacket
-  var that = this
-  var writable = new Writable()
-  var parser = mqttPacket.parser(this.options)
-  var completeParse = null
-  var packets = []
+  const that = this
+  const writable = new Writable()
+  const parser = mqttPacket.parser(this.options)
+  let completeParse = null
+  const packets = []
 
   debug('_setupStream :: calling method to clear reconnect')
   this._clearReconnect()
@@ -422,7 +421,7 @@ MqttClient.prototype._setupStream = function () {
     if (packets.length) {
       nextTick(work)
     } else {
-      var done = completeParse
+      const done = completeParse
       completeParse = null
       done()
     }
@@ -430,14 +429,14 @@ MqttClient.prototype._setupStream = function () {
 
   function work () {
     debug('work :: getting next packet in queue')
-    var packet = packets.shift()
+    const packet = packets.shift()
 
     if (packet) {
       debug('work :: packet pulled from queue')
       that._handlePacket(packet, nextTickWork)
     } else {
       debug('work :: no packets in queue')
-      var done = completeParse
+      const done = completeParse
       completeParse = null
       debug('work :: done flag is %s', !!(done))
       if (done) done()
@@ -478,7 +477,7 @@ MqttClient.prototype._setupStream = function () {
 
   // Send a connect packet
   debug('_setupStream: sending packet `connect`')
-  connectPacket = Object.create(this.options)
+  const connectPacket = Object.create(this.options)
   connectPacket.cmd = 'connect'
   if (this.topicAliasRecv) {
     if (!connectPacket.properties) {
@@ -503,7 +502,7 @@ MqttClient.prototype._setupStream = function () {
       return this
     }
     if (this.options.properties.authenticationMethod && this.options.authPacket && typeof this.options.authPacket === 'object') {
-      var authPacket = xtend({cmd: 'auth', reasonCode: 0}, this.options.authPacket)
+      const authPacket = xtend({ cmd: 'auth', reasonCode: 0 }, this.options.authPacket)
       sendPacket(this, authPacket)
     }
   }
@@ -519,11 +518,11 @@ MqttClient.prototype._setupStream = function () {
 }
 
 MqttClient.prototype._handlePacket = function (packet, done) {
-  var options = this.options
+  const options = this.options
 
   if (options.protocolVersion === 5 && options.properties && options.properties.maximumPacketSize && options.properties.maximumPacketSize < packet.length) {
     this.emit('error', new Error('exceeding packets size ' + packet.cmd))
-    this.end({reasonCode: 149, properties: { reasonString: 'Maximum packet size was exceeded' }})
+    this.end({ reasonCode: 149, properties: { reasonString: 'Maximum packet size was exceeded' } })
     return this
   }
   debug('_handlePacket :: emitting packetreceive')
@@ -597,8 +596,7 @@ MqttClient.prototype._checkDisconnecting = function (callback) {
  */
 MqttClient.prototype.publish = function (topic, message, opts, callback) {
   debug('publish :: message `%s` to topic `%s`', message, topic)
-  var packet
-  var options = this.options
+  const options = this.options
 
   // .publish(topic, payload, cb);
   if (typeof opts === 'function') {
@@ -607,16 +605,16 @@ MqttClient.prototype.publish = function (topic, message, opts, callback) {
   }
 
   // default opts
-  var defaultOpts = {qos: 0, retain: false, dup: false}
+  const defaultOpts = { qos: 0, retain: false, dup: false }
   opts = xtend(defaultOpts, opts)
 
   if (this._checkDisconnecting(callback)) {
     return this
   }
 
-  var that = this
-  var publishProc = function () {
-    var messageId = 0
+  const that = this
+  const publishProc = function () {
+    let messageId = 0
     if (opts.qos === 1 || opts.qos === 2) {
       messageId = that._nextId()
       if (messageId === null) {
@@ -624,7 +622,7 @@ MqttClient.prototype.publish = function (topic, message, opts, callback) {
         return false
       }
     }
-    packet = {
+    const packet = {
       cmd: 'publish',
       topic: topic,
       payload: message,
@@ -661,9 +659,9 @@ MqttClient.prototype.publish = function (topic, message, opts, callback) {
   if (this._storeProcessing || this._storeProcessingQueue.length > 0) {
     this._storeProcessingQueue.push(
       {
-        'invoke': publishProc,
-        'cbStorePut': opts.cbStorePut,
-        'callback': callback
+        invoke: publishProc,
+        cbStorePut: opts.cbStorePut,
+        callback: callback
       }
     )
   } else {
@@ -689,17 +687,17 @@ MqttClient.prototype.publish = function (topic, message, opts, callback) {
  * @example client.subscribe('topic', console.log);
  */
 MqttClient.prototype.subscribe = function () {
-  var that = this
-  var args = new Array(arguments.length)
-  for (var i = 0; i < arguments.length; i++) {
+  const that = this
+  const args = new Array(arguments.length)
+  for (let i = 0; i < arguments.length; i++) {
     args[i] = arguments[i]
   }
-  var subs = []
-  var obj = args.shift()
-  var resubscribe = obj.resubscribe
-  var callback = args.pop() || nop
-  var opts = args.pop()
-  var version = this.options.protocolVersion
+  const subs = []
+  let obj = args.shift()
+  const resubscribe = obj.resubscribe
+  let callback = args.pop() || nop
+  let opts = args.pop()
+  const version = this.options.protocolVersion
 
   delete obj.resubscribe
 
@@ -712,7 +710,7 @@ MqttClient.prototype.subscribe = function () {
     callback = nop
   }
 
-  var invalidTopic = validations.validateTopics(obj)
+  const invalidTopic = validations.validateTopics(obj)
   if (invalidTopic !== null) {
     setImmediate(callback, new Error('Invalid topic ' + invalidTopic))
     return this
@@ -723,7 +721,7 @@ MqttClient.prototype.subscribe = function () {
     return this
   }
 
-  var defaultOpts = {
+  const defaultOpts = {
     qos: 0
   }
   if (version === 5) {
@@ -736,10 +734,10 @@ MqttClient.prototype.subscribe = function () {
   if (Array.isArray(obj)) {
     obj.forEach(function (topic) {
       debug('subscribe: array topic %s', topic)
-      if (!that._resubscribeTopics.hasOwnProperty(topic) ||
+      if (!Object.prototype.hasOwnProperty.call(that._resubscribeTopics, topic) ||
         that._resubscribeTopics[topic].qos < opts.qos ||
           resubscribe) {
-        var currentOpts = {
+        const currentOpts = {
           topic: topic,
           qos: opts.qos
         }
@@ -758,10 +756,10 @@ MqttClient.prototype.subscribe = function () {
       .keys(obj)
       .forEach(function (k) {
         debug('subscribe: object topic %s', k)
-        if (!that._resubscribeTopics.hasOwnProperty(k) ||
+        if (!Object.prototype.hasOwnProperty.call(that._resubscribeTopics, k) ||
           that._resubscribeTopics[k].qos < obj[k].qos ||
             resubscribe) {
-          var currentOpts = {
+          const currentOpts = {
             topic: k,
             qos: obj[k].qos
           }
@@ -782,14 +780,14 @@ MqttClient.prototype.subscribe = function () {
     return this
   }
 
-  var subscribeProc = function () {
-    var messageId = that._nextId()
+  const subscribeProc = function () {
+    const messageId = that._nextId()
     if (messageId === null) {
       debug('No messageId left')
       return false
     }
 
-    var packet = {
+    const packet = {
       cmd: 'subscribe',
       subscriptions: subs,
       qos: 1,
@@ -805,10 +803,10 @@ MqttClient.prototype.subscribe = function () {
     // subscriptions to resubscribe to in case of disconnect
     if (that.options.resubscribe) {
       debug('subscribe :: resubscribe true')
-      var topics = []
+      const topics = []
       subs.forEach(function (sub) {
         if (that.options.reconnectPeriod > 0) {
-          var topic = { qos: sub.qos }
+          const topic = { qos: sub.qos }
           if (version === 5) {
             topic.nl = sub.nl || false
             topic.rap = sub.rap || false
@@ -826,8 +824,8 @@ MqttClient.prototype.subscribe = function () {
       volatile: true,
       cb: function (err, packet) {
         if (!err) {
-          var granted = packet.granted
-          for (var i = 0; i < granted.length; i += 1) {
+          const granted = packet.granted
+          for (let i = 0; i < granted.length; i += 1) {
             subs[i].qos = granted[i]
           }
         }
@@ -843,8 +841,8 @@ MqttClient.prototype.subscribe = function () {
   if (this._storeProcessing || this._storeProcessingQueue.length > 0) {
     this._storeProcessingQueue.push(
       {
-        'invoke': subscribeProc,
-        'callback': callback
+        invoke: subscribeProc,
+        callback: callback
       }
     )
   } else {
@@ -867,14 +865,14 @@ MqttClient.prototype.subscribe = function () {
  * @example client.unsubscribe('topic', console.log);
  */
 MqttClient.prototype.unsubscribe = function () {
-  var that = this
-  var args = new Array(arguments.length)
-  for (var i = 0; i < arguments.length; i++) {
+  const that = this
+  const args = new Array(arguments.length)
+  for (let i = 0; i < arguments.length; i++) {
     args[i] = arguments[i]
   }
-  var topic = args.shift()
-  var callback = args.pop() || nop
-  var opts = args.pop()
+  let topic = args.shift()
+  let callback = args.pop() || nop
+  let opts = args.pop()
   if (typeof topic === 'string') {
     topic = [topic]
   }
@@ -884,7 +882,7 @@ MqttClient.prototype.unsubscribe = function () {
     callback = nop
   }
 
-  var invalidTopic = validations.validateTopics(topic)
+  const invalidTopic = validations.validateTopics(topic)
   if (invalidTopic !== null) {
     setImmediate(callback, new Error('Invalid topic ' + invalidTopic))
     return this
@@ -894,13 +892,13 @@ MqttClient.prototype.unsubscribe = function () {
     return this
   }
 
-  var unsubscribeProc = function () {
-    var messageId = that._nextId()
+  const unsubscribeProc = function () {
+    const messageId = that._nextId()
     if (messageId === null) {
       debug('No messageId left')
       return false
     }
-    var packet = {
+    const packet = {
       cmd: 'unsubscribe',
       qos: 1,
       messageId: messageId
@@ -936,8 +934,8 @@ MqttClient.prototype.unsubscribe = function () {
   if (this._storeProcessing || this._storeProcessingQueue.length > 0) {
     this._storeProcessingQueue.push(
       {
-        'invoke': unsubscribeProc,
-        'callback': callback
+        invoke: unsubscribeProc,
+        callback: callback
       }
     )
   } else {
@@ -958,7 +956,7 @@ MqttClient.prototype.unsubscribe = function () {
  * @api public
  */
 MqttClient.prototype.end = function (force, opts, cb) {
-  var that = this
+  const that = this
 
   debug('end :: (%s)', this.options.clientId)
 
@@ -991,7 +989,7 @@ MqttClient.prototype.end = function (force, opts, cb) {
         debug('end :: closeStores: emitting end')
         that.emit('end')
         if (cb) {
-          let err = e1 || e2
+          const err = e1 || e2
           debug('end :: closeStores: invoking callback with args')
           cb(err)
         }
@@ -1009,7 +1007,7 @@ MqttClient.prototype.end = function (force, opts, cb) {
     debug('end :: (%s) :: finish :: calling _cleanUp with force %s', that.options.clientId, force)
     that._cleanUp(force, () => {
       debug('end :: finish :: calling process.nextTick on closeStores')
-      // var boundProcess = nextTick.bind(null, closeStores)
+      // const boundProcess = nextTick.bind(null, closeStores)
       nextTick(closeStores.bind(that))
     }, opts)
   }
@@ -1046,9 +1044,9 @@ MqttClient.prototype.end = function (force, opts, cb) {
  * @example client.removeOutgoingMessage(client.getLastAllocated());
  */
 MqttClient.prototype.removeOutgoingMessage = function (messageId) {
-  var cb = this.outgoing[messageId] ? this.outgoing[messageId].cb : null
+  const cb = this.outgoing[messageId] ? this.outgoing[messageId].cb : null
   delete this.outgoing[messageId]
-  this.outgoingStore.del({messageId: messageId}, function () {
+  this.outgoingStore.del({ messageId: messageId }, function () {
     cb(new Error('Message removed'))
   })
   return this
@@ -1067,8 +1065,8 @@ MqttClient.prototype.removeOutgoingMessage = function (messageId) {
  */
 MqttClient.prototype.reconnect = function (opts) {
   debug('client reconnect')
-  var that = this
-  var f = function () {
+  const that = this
+  const f = function () {
     if (opts) {
       that.options.incomingStore = opts.incomingStore
       that.options.outgoingStore = opts.outgoingStore
@@ -1112,7 +1110,7 @@ MqttClient.prototype._reconnect = function () {
  * _setupReconnect - setup reconnect timer
  */
 MqttClient.prototype._setupReconnect = function () {
-  var that = this
+  const that = this
 
   if (!that.disconnecting && !that.reconnectTimer && (that.options.reconnectPeriod > 0)) {
     if (!this.reconnecting) {
@@ -1147,7 +1145,7 @@ MqttClient.prototype._clearReconnect = function () {
  * @api private
  */
 MqttClient.prototype._cleanUp = function (forced, done) {
-  var opts = arguments[2]
+  const opts = arguments[2]
   if (done) {
     debug('_cleanUp :: done callback provided for on stream close')
     this.stream.on('close', done)
@@ -1161,7 +1159,7 @@ MqttClient.prototype._cleanUp = function (forced, done) {
     debug('_cleanUp :: (%s) :: destroying stream', this.options.clientId)
     this.stream.destroy()
   } else {
-    var packet = xtend({ cmd: 'disconnect' }, opts)
+    const packet = xtend({ cmd: 'disconnect' }, opts)
     debug('_cleanUp :: (%s) :: call _sendPacket with disconnect packet', this.options.clientId)
     this._sendPacket(
       packet,
@@ -1203,7 +1201,7 @@ MqttClient.prototype._sendPacket = function (packet, cb, cbStorePut) {
   cbStorePut = cbStorePut || nop
   cb = cb || nop
 
-  var err = applyTopicAlias(this, packet)
+  const err = applyTopicAlias(this, packet)
   if (err) {
     cb(err)
     return
@@ -1260,13 +1258,13 @@ MqttClient.prototype._storePacket = function (packet, cb, cbStorePut) {
   debug('_storePacket :: cb? %s', !!cb)
   cbStorePut = cbStorePut || nop
 
-  var storePacket = packet
+  let storePacket = packet
   if (storePacket.cmd === 'publish') {
     // The original packet is for sending.
     // The cloned storePacket is for storing to resend on reconnect.
     // Topic Alias must not be used after disconnected.
     storePacket = clone(packet)
-    var err = removeTopicAliasAndRecoverTopicName(this, storePacket)
+    const err = removeTopicAliasAndRecoverTopicName(this, storePacket)
     if (err) {
       return cb && cb(err)
     }
@@ -1294,7 +1292,7 @@ MqttClient.prototype._storePacket = function (packet, cb, cbStorePut) {
  */
 MqttClient.prototype._setupPingTimer = function () {
   debug('_setupPingTimer :: keepalive %d (seconds)', this.options.keepalive)
-  var that = this
+  const that = this
 
   if (!this.pingTimer && this.options.keepalive) {
     this.pingResp = true
@@ -1349,9 +1347,9 @@ MqttClient.prototype._handlePingresp = function () {
  */
 MqttClient.prototype._handleConnack = function (packet) {
   debug('_handleConnack')
-  var options = this.options
-  var version = options.protocolVersion
-  var rc = version === 5 ? packet.reasonCode : packet.returnCode
+  const options = this.options
+  const version = options.protocolVersion
+  const rc = version === 5 ? packet.reasonCode : packet.returnCode
 
   clearTimeout(this.connackTimer)
   delete this.topicAliasSend
@@ -1380,7 +1378,7 @@ MqttClient.prototype._handleConnack = function (packet) {
     this.reconnecting = false
     this._onConnect(packet)
   } else if (rc > 0) {
-    var err = new Error('Connection refused: ' + errors[rc])
+    const err = new Error('Connection refused: ' + errors[rc])
     err.code = rc
     this.emit('error', err)
   }
@@ -1419,22 +1417,22 @@ for now i just suppressed the warnings
 MqttClient.prototype._handlePublish = function (packet, done) {
   debug('_handlePublish: packet %o', packet)
   done = typeof done !== 'undefined' ? done : nop
-  var topic = packet.topic.toString()
-  var message = packet.payload
-  var qos = packet.qos
-  var messageId = packet.messageId
-  var that = this
-  var options = this.options
-  var validReasonCodes = [0, 16, 128, 131, 135, 144, 145, 151, 153]
+  let topic = packet.topic.toString()
+  const message = packet.payload
+  const qos = packet.qos
+  const messageId = packet.messageId
+  const that = this
+  const options = this.options
+  const validReasonCodes = [0, 16, 128, 131, 135, 144, 145, 151, 153]
   if (this.options.protocolVersion === 5) {
-    var alias
+    let alias
     if (packet.properties) {
       alias = packet.properties.topicAlias
     }
     if (typeof alias !== 'undefined') {
       if (topic.length === 0) {
         if (alias > 0 && alias <= 0xffff) {
-          var gotTopic = this.topicAliasRecv.getTopicByAlias(alias)
+          const gotTopic = this.topicAliasRecv.getTopicByAlias(alias)
           if (gotTopic) {
             topic = gotTopic
             debug('_handlePublish :: topic complemented by alias. topic: %s - alias: %d', topic, alias)
@@ -1470,10 +1468,10 @@ MqttClient.prototype._handlePublish = function (packet, done) {
         if (error) { return that.emit('error', error) }
         if (validReasonCodes.indexOf(code) === -1) { return that.emit('error', new Error('Wrong reason code for pubrec')) }
         if (code) {
-          that._sendPacket({cmd: 'pubrec', messageId: messageId, reasonCode: code}, done)
+          that._sendPacket({ cmd: 'pubrec', messageId: messageId, reasonCode: code }, done)
         } else {
           that.incomingStore.put(packet, function () {
-            that._sendPacket({cmd: 'pubrec', messageId: messageId}, done)
+            that._sendPacket({ cmd: 'pubrec', messageId: messageId }, done)
           })
         }
       })
@@ -1493,7 +1491,7 @@ MqttClient.prototype._handlePublish = function (packet, done) {
           if (err) {
             return done && done(err)
           }
-          that._sendPacket({cmd: 'puback', messageId: messageId, reasonCode: code}, done)
+          that._sendPacket({ cmd: 'puback', messageId: messageId, reasonCode: code }, done)
         })
       })
       break
@@ -1532,12 +1530,12 @@ MqttClient.prototype.handleMessage = function (packet, callback) {
 
 MqttClient.prototype._handleAck = function (packet) {
   /* eslint no-fallthrough: "off" */
-  var messageId = packet.messageId
-  var type = packet.cmd
-  var response = null
-  var cb = this.outgoing[messageId] ? this.outgoing[messageId].cb : null
-  var that = this
-  var err
+  const messageId = packet.messageId
+  const type = packet.cmd
+  let response = null
+  const cb = this.outgoing[messageId] ? this.outgoing[messageId].cb : null
+  const that = this
+  let err
 
   if (!cb) {
     debug('_handleAck :: Server sent an ack in error. Ignoring.')
@@ -1550,8 +1548,8 @@ MqttClient.prototype._handleAck = function (packet) {
   switch (type) {
     case 'pubcomp':
       // same thing as puback for QoS 2
-    case 'puback':
-      var pubackRC = packet.reasonCode
+    case 'puback': {
+      const pubackRC = packet.reasonCode
       // Callback - we're done
       if (pubackRC && pubackRC > 0 && pubackRC !== 16) {
         err = new Error('Publish error: ' + errors[pubackRC])
@@ -1563,13 +1561,14 @@ MqttClient.prototype._handleAck = function (packet) {
       this.messageIdProvider.deallocate(messageId)
       this._invokeStoreProcessingQueue()
       break
-    case 'pubrec':
+    }
+    case 'pubrec': {
       response = {
         cmd: 'pubrel',
         qos: 2,
         messageId: messageId
       }
-      var pubrecRC = packet.reasonCode
+      const pubrecRC = packet.reasonCode
 
       if (pubrecRC && pubrecRC > 0 && pubrecRC !== 16) {
         err = new Error('Publish error: ' + errors[pubrecRC])
@@ -1579,13 +1578,14 @@ MqttClient.prototype._handleAck = function (packet) {
         this._sendPacket(response)
       }
       break
-    case 'suback':
+    }
+    case 'suback': {
       delete this.outgoing[messageId]
       this.messageIdProvider.deallocate(messageId)
-      for (var grantedI = 0; grantedI < packet.granted.length; grantedI++) {
+      for (let grantedI = 0; grantedI < packet.granted.length; grantedI++) {
         if ((packet.granted[grantedI] & 0x80) !== 0) {
           // suback with Failure status
-          var topics = this.messageIdToTopic[messageId]
+          const topics = this.messageIdToTopic[messageId]
           if (topics) {
             topics.forEach(function (topic) {
               delete that._resubscribeTopics[topic]
@@ -1596,12 +1596,14 @@ MqttClient.prototype._handleAck = function (packet) {
       this._invokeStoreProcessingQueue()
       cb(null, packet)
       break
-    case 'unsuback':
+    }
+    case 'unsuback': {
       delete this.outgoing[messageId]
       this.messageIdProvider.deallocate(messageId)
       this._invokeStoreProcessingQueue()
       cb(null)
       break
+    }
     default:
       that.emit('error', new Error('unrecognized packet type'))
   }
@@ -1621,10 +1623,10 @@ MqttClient.prototype._handleAck = function (packet) {
 MqttClient.prototype._handlePubrel = function (packet, callback) {
   debug('handling pubrel packet')
   callback = typeof callback !== 'undefined' ? callback : nop
-  var messageId = packet.messageId
-  var that = this
+  const messageId = packet.messageId
+  const that = this
 
-  var comp = {cmd: 'pubcomp', messageId: messageId}
+  const comp = { cmd: 'pubcomp', messageId: messageId }
 
   that.incomingStore.get(packet, function (err, pub) {
     if (!err) {
@@ -1674,18 +1676,18 @@ MqttClient.prototype.getLastMessageId = function () {
  */
 MqttClient.prototype._resubscribe = function () {
   debug('_resubscribe')
-  var _resubscribeTopicsKeys = Object.keys(this._resubscribeTopics)
+  const _resubscribeTopicsKeys = Object.keys(this._resubscribeTopics)
   if (!this._firstConnection &&
       (this.options.clean || (this.options.protocolVersion === 5 && !this.connackPacket.sessionPresent)) &&
       _resubscribeTopicsKeys.length > 0) {
     if (this.options.resubscribe) {
       if (this.options.protocolVersion === 5) {
         debug('_resubscribe: protocolVersion 5')
-        for (var topicI = 0; topicI < _resubscribeTopicsKeys.length; topicI++) {
-          var resubscribeTopic = {}
+        for (let topicI = 0; topicI < _resubscribeTopicsKeys.length; topicI++) {
+          const resubscribeTopic = {}
           resubscribeTopic[_resubscribeTopicsKeys[topicI]] = this._resubscribeTopics[_resubscribeTopicsKeys[topicI]]
           resubscribeTopic.resubscribe = true
-          this.subscribe(resubscribeTopic, {properties: resubscribeTopic[_resubscribeTopicsKeys[topicI]].properties})
+          this.subscribe(resubscribeTopic, { properties: resubscribeTopic[_resubscribeTopicsKeys[topicI]].properties })
         }
       } else {
         this._resubscribeTopics.resubscribe = true
@@ -1710,7 +1712,7 @@ MqttClient.prototype._onConnect = function (packet) {
     return
   }
 
-  var that = this
+  const that = this
 
   this.connackPacket = packet
   this.messageIdProvider.clear()
@@ -1719,7 +1721,7 @@ MqttClient.prototype._onConnect = function (packet) {
   this.connected = true
 
   function startStreamProcess () {
-    var outStore = that.outgoingStore.createStream()
+    let outStore = that.outgoingStore.createStream()
 
     function clearStoreProcessing () {
       that._storeProcessing = false
@@ -1748,9 +1750,9 @@ MqttClient.prototype._onConnect = function (packet) {
       }
       that._storeProcessing = true
 
-      var packet = outStore.read(1)
+      const packet = outStore.read(1)
 
-      var cb
+      let cb
 
       if (!packet) {
         // read when data is available in the future
@@ -1790,8 +1792,8 @@ MqttClient.prototype._onConnect = function (packet) {
     }
 
     outStore.on('end', function () {
-      var allProcessed = true
-      for (var id in that._packetIdsDuringStoreProcessing) {
+      let allProcessed = true
+      for (const id in that._packetIdsDuringStoreProcessing) {
         if (!that._packetIdsDuringStoreProcessing[id]) {
           allProcessed = false
           break
@@ -1814,7 +1816,7 @@ MqttClient.prototype._onConnect = function (packet) {
 
 MqttClient.prototype._invokeStoreProcessingQueue = function () {
   if (this._storeProcessingQueue.length > 0) {
-    var f = this._storeProcessingQueue[0]
+    const f = this._storeProcessingQueue[0]
     if (f && f.invoke()) {
       this._storeProcessingQueue.shift()
       return true
@@ -1824,11 +1826,11 @@ MqttClient.prototype._invokeStoreProcessingQueue = function () {
 }
 
 MqttClient.prototype._invokeAllStoreProcessingQueue = function () {
-  while (this._invokeStoreProcessingQueue()) {}
+  while (this._invokeStoreProcessingQueue()) { /* empty */ }
 }
 
 MqttClient.prototype._flushStoreProcessingQueue = function () {
-  for (var f of this._storeProcessingQueue) {
+  for (const f of this._storeProcessingQueue) {
     if (f.cbStorePut) f.cbStorePut(new Error('Connection closed'))
     if (f.callback) f.callback(new Error('Connection closed'))
   }
diff --git a/lib/connect/ali.js b/lib/connect/ali.js
index e7fe6a3c5..aae76acf1 100644
--- a/lib/connect/ali.js
+++ b/lib/connect/ali.js
@@ -1,16 +1,16 @@
 'use strict'
 
-var Transform = require('readable-stream').Transform
-var duplexify = require('duplexify')
+const Transform = require('readable-stream').Transform
+const duplexify = require('duplexify')
 
 /* global FileReader */
-var my
-var proxy
-var stream
-var isInitialized = false
+let my
+let proxy
+let stream
+let isInitialized = false
 
 function buildProxy () {
-  var proxy = new Transform()
+  const proxy = new Transform()
   proxy._write = function (chunk, encoding, next) {
     my.sendSocketMessage({
       data: chunk.buffer,
@@ -47,8 +47,8 @@ function setDefaultOpts (opts) {
 }
 
 function buildUrl (opts, client) {
-  var protocol = opts.protocol === 'alis' ? 'wss' : 'ws'
-  var url = protocol + '://' + opts.hostname + opts.path
+  const protocol = opts.protocol === 'alis' ? 'wss' : 'ws'
+  let url = protocol + '://' + opts.hostname + opts.path
   if (opts.port && opts.port !== 80 && opts.port !== 443) {
     url = protocol + '://' + opts.hostname + ':' + opts.port + opts.path
   }
@@ -71,12 +71,12 @@ function bindEventHandler () {
 
   my.onSocketMessage(function (res) {
     if (typeof res.data === 'string') {
-      var buffer = Buffer.from(res.data, 'base64')
+      const buffer = Buffer.from(res.data, 'base64')
       proxy.push(buffer)
     } else {
-      var reader = new FileReader()
+      const reader = new FileReader()
       reader.addEventListener('load', function () {
-        var data = reader.result
+        let data = reader.result
 
         if (data instanceof ArrayBuffer) data = Buffer.from(data)
         else data = Buffer.from(data, 'utf8')
@@ -103,14 +103,14 @@ function buildStream (client, opts) {
     throw new Error('Could not determine host. Specify host manually.')
   }
 
-  var websocketSubProtocol =
+  const websocketSubProtocol =
     (opts.protocolId === 'MQIsdp') && (opts.protocolVersion === 3)
       ? 'mqttv3.1'
       : 'mqtt'
 
   setDefaultOpts(opts)
 
-  var url = buildUrl(opts, client)
+  const url = buildUrl(opts, client)
   my = opts.my
   my.connectSocket({
     url: url,
diff --git a/lib/connect/index.js b/lib/connect/index.js
index 97e7b4c15..585b26c5c 100644
--- a/lib/connect/index.js
+++ b/lib/connect/index.js
@@ -1,12 +1,12 @@
 'use strict'
 
-var MqttClient = require('../client')
-var Store = require('../store')
-var url = require('url')
-var xtend = require('xtend')
-var debug = require('debug')('mqttjs')
+const MqttClient = require('../client')
+const Store = require('../store')
+const url = require('url')
+const xtend = require('xtend')
+const debug = require('debug')('mqttjs')
 
-var protocols = {}
+const protocols = {}
 
 // eslint-disable-next-line camelcase
 if ((typeof process !== 'undefined' && process.title !== 'browser') || typeof __webpack_require__ !== 'function') {
@@ -32,7 +32,7 @@ protocols.wss = require('./ws')
  * @param {Object} [opts] option object
  */
 function parseAuthOptions (opts) {
-  var matches
+  let matches
   if (opts.auth) {
     matches = opts.auth.match(/^(.+):(.+)$/)
     if (matches) {
@@ -60,7 +60,8 @@ function connect (brokerUrl, opts) {
   opts = opts || {}
 
   if (brokerUrl) {
-    var parsed = url.parse(brokerUrl, true)
+    // eslint-disable-next-line
+    const parsed = url.parse(brokerUrl, true)
     if (parsed.port != null) {
       parsed.port = Number(parsed.port)
     }
@@ -109,7 +110,7 @@ function connect (brokerUrl, opts) {
   }
 
   if (!protocols[opts.protocol]) {
-    var isSecure = ['mqtts', 'wss'].indexOf(opts.protocol) !== -1
+    const isSecure = ['mqtts', 'wss'].indexOf(opts.protocol) !== -1
     opts.protocol = [
       'mqtt',
       'mqtts',
@@ -153,7 +154,7 @@ function connect (brokerUrl, opts) {
     debug('calling streambuilder for', opts.protocol)
     return protocols[opts.protocol](client, opts)
   }
-  var client = new MqttClient(wrapper, opts)
+  const client = new MqttClient(wrapper, opts)
   client.on('error', function () { /* Automatically set up client error handling */ })
   return client
 }
diff --git a/lib/connect/tcp.js b/lib/connect/tcp.js
index 9912102eb..607036537 100644
--- a/lib/connect/tcp.js
+++ b/lib/connect/tcp.js
@@ -1,18 +1,17 @@
 'use strict'
-var net = require('net')
-var debug = require('debug')('mqttjs:tcp')
+const net = require('net')
+const debug = require('debug')('mqttjs:tcp')
 
 /*
   variables port and host can be removed since
   you have all required information in opts object
 */
 function streamBuilder (client, opts) {
-  var port, host
   opts.port = opts.port || 1883
   opts.hostname = opts.hostname || opts.host || 'localhost'
 
-  port = opts.port
-  host = opts.hostname
+  const port = opts.port
+  const host = opts.hostname
 
   debug('port %d and host %s', port, host)
   return net.createConnection(port, host)
diff --git a/lib/connect/tls.js b/lib/connect/tls.js
index ccf3731cd..bb01aeb8f 100644
--- a/lib/connect/tls.js
+++ b/lib/connect/tls.js
@@ -1,14 +1,13 @@
 'use strict'
-var tls = require('tls')
-var net = require('net')
-var debug = require('debug')('mqttjs:tls')
+const tls = require('tls')
+const net = require('net')
+const debug = require('debug')('mqttjs:tls')
 
 function buildBuilder (mqttClient, opts) {
-  var connection
   opts.port = opts.port || 8883
   opts.host = opts.hostname || opts.host || 'localhost'
 
-  if(net.isIP(opts.host) === 0){
+  if (net.isIP(opts.host) === 0) {
     opts.servername = opts.host
   }
 
@@ -18,7 +17,7 @@ function buildBuilder (mqttClient, opts) {
 
   debug('port %d host %s rejectUnauthorized %b', opts.port, opts.host, opts.rejectUnauthorized)
 
-  connection = tls.connect(opts)
+  const connection = tls.connect(opts)
   /* eslint no-use-before-define: [2, "nofunc"] */
   connection.on('secureConnect', function () {
     if (opts.rejectUnauthorized && !connection.authorized) {
diff --git a/lib/connect/ws.js b/lib/connect/ws.js
index 5c1d2c691..c7e2e15f8 100644
--- a/lib/connect/ws.js
+++ b/lib/connect/ws.js
@@ -5,7 +5,7 @@ const debug = require('debug')('mqttjs:ws')
 const duplexify = require('duplexify')
 const Transform = require('readable-stream').Transform
 
-let WSS_OPTIONS = [
+const WSS_OPTIONS = [
   'rejectUnauthorized',
   'ca',
   'cert',
@@ -24,7 +24,7 @@ function buildUrl (opts, client) {
 }
 
 function setDefaultOpts (opts) {
-  let options = opts
+  const options = opts
   if (!opts.hostname) {
     options.hostname = 'localhost'
   }
@@ -45,7 +45,7 @@ function setDefaultOpts (opts) {
   if (!IS_BROWSER && opts.protocol === 'wss') {
     // Add cert/key/ca etc options
     WSS_OPTIONS.forEach(function (prop) {
-      if (opts.hasOwnProperty(prop) && !opts.wsOptions.hasOwnProperty(prop)) {
+      if (Object.prototype.hasOwnProperty.call(opts, prop) && !Object.prototype.hasOwnProperty.call(opts.wsOptions, prop)) {
         options.wsOptions[prop] = opts[prop]
       }
     })
@@ -55,7 +55,7 @@ function setDefaultOpts (opts) {
 }
 
 function setDefaultBrowserOpts (opts) {
-  let options = setDefaultOpts(opts)
+  const options = setDefaultOpts(opts)
 
   if (!options.hostname) {
     options.hostname = options.host
@@ -93,7 +93,7 @@ function createWebSocket (client, url, opts) {
       : 'mqtt'
 
   debug('creating new Websocket for url: ' + url + ' and protocol: ' + websocketSubProtocol)
-  let socket = new WS(url, [websocketSubProtocol], opts.wsOptions)
+  const socket = new WS(url, [websocketSubProtocol], opts.wsOptions)
   return socket
 }
 
@@ -103,19 +103,19 @@ function createBrowserWebSocket (client, opts) {
     ? 'mqttv3.1'
     : 'mqtt'
 
-  let url = buildUrl(opts, client)
+  const url = buildUrl(opts, client)
   /* global WebSocket */
-  let socket = new WebSocket(url, [websocketSubProtocol])
+  const socket = new WebSocket(url, [websocketSubProtocol])
   socket.binaryType = 'arraybuffer'
   return socket
 }
 
 function streamBuilder (client, opts) {
   debug('streamBuilder')
-  let options = setDefaultOpts(opts)
+  const options = setDefaultOpts(opts)
   const url = buildUrl(options, client)
-  let socket = createWebSocket(client, url, options)
-  let webSocketStream = WS.createWebSocketStream(socket, options.wsOptions)
+  const socket = createWebSocket(client, url, options)
+  const webSocketStream = WS.createWebSocketStream(socket, options.wsOptions)
   webSocketStream.url = url
   socket.on('close', () => { webSocketStream.destroy() })
   return webSocketStream
@@ -124,7 +124,7 @@ function streamBuilder (client, opts) {
 function browserStreamBuilder (client, opts) {
   debug('browserStreamBuilder')
   let stream
-  let options = setDefaultBrowserOpts(opts)
+  const options = setDefaultBrowserOpts(opts)
   // sets the maximum socket buffer size before throttling
   const bufferSize = options.browserBufferSize || 1024 * 512
 
@@ -132,9 +132,9 @@ function browserStreamBuilder (client, opts) {
 
   const coerceToBuffer = !opts.objectMode
 
-  let socket = createBrowserWebSocket(client, opts)
+  const socket = createBrowserWebSocket(client, opts)
 
-  let proxy = buildProxy(opts, socketWriteBrowser, socketEndBrowser)
+  const proxy = buildProxy(opts, socketWriteBrowser, socketEndBrowser)
 
   if (!opts.objectMode) {
     proxy._writev = writev
@@ -174,7 +174,7 @@ function browserStreamBuilder (client, opts) {
   // methods for browserStreamBuilder
 
   function buildProxy (options, socketWrite, socketEnd) {
-    let proxy = new Transform({
+    const proxy = new Transform({
       objectModeMode: options.objectMode
     })
 
diff --git a/lib/connect/wx.js b/lib/connect/wx.js
index b9c7a0705..61b38e473 100644
--- a/lib/connect/wx.js
+++ b/lib/connect/wx.js
@@ -1,15 +1,13 @@
 'use strict'
 
-var Transform = require('readable-stream').Transform
-var duplexify = require('duplexify')
+const Transform = require('readable-stream').Transform
+const duplexify = require('duplexify')
 
 /* global wx */
-var socketTask
-var proxy
-var stream
+let socketTask, proxy, stream
 
 function buildProxy () {
-  var proxy = new Transform()
+  const proxy = new Transform()
   proxy._write = function (chunk, encoding, next) {
     socketTask.send({
       data: chunk.buffer,
@@ -46,8 +44,8 @@ function setDefaultOpts (opts) {
 }
 
 function buildUrl (opts, client) {
-  var protocol = opts.protocol === 'wxs' ? 'wss' : 'ws'
-  var url = protocol + '://' + opts.hostname + opts.path
+  const protocol = opts.protocol === 'wxs' ? 'wss' : 'ws'
+  let url = protocol + '://' + opts.hostname + opts.path
   if (opts.port && opts.port !== 80 && opts.port !== 443) {
     url = protocol + '://' + opts.hostname + ':' + opts.port + opts.path
   }
@@ -65,7 +63,7 @@ function bindEventHandler () {
   })
 
   socketTask.onMessage(function (res) {
-    var data = res.data
+    let data = res.data
 
     if (data instanceof ArrayBuffer) data = Buffer.from(data)
     else data = Buffer.from(data, 'utf8')
@@ -89,14 +87,14 @@ function buildStream (client, opts) {
     throw new Error('Could not determine host. Specify host manually.')
   }
 
-  var websocketSubProtocol =
+  const websocketSubProtocol =
     (opts.protocolId === 'MQIsdp') && (opts.protocolVersion === 3)
       ? 'mqttv3.1'
       : 'mqtt'
 
   setDefaultOpts(opts)
 
-  var url = buildUrl(opts, client)
+  const url = buildUrl(opts, client)
   socketTask = wx.connectSocket({
     url: url,
     protocols: [websocketSubProtocol]
@@ -112,11 +110,11 @@ function buildStream (client, opts) {
     })
   }
 
-  var destroyRef = stream.destroy
+  const destroyRef = stream.destroy
   stream.destroy = function () {
     stream.destroy = destroyRef
 
-    var self = this
+    const self = this
     setTimeout(function () {
       socketTask.close({
         fail: function () {
diff --git a/lib/default-message-id-provider.js b/lib/default-message-id-provider.js
index c0a953f3f..3655983a0 100644
--- a/lib/default-message-id-provider.js
+++ b/lib/default-message-id-provider.js
@@ -24,7 +24,7 @@ function DefaultMessageIdProvider () {
  */
 DefaultMessageIdProvider.prototype.allocate = function () {
   // id becomes current state of this.nextId and increments afterwards
-  var id = this.nextId++
+  const id = this.nextId++
   // Ensure 16 bit unsigned int (max 65535, nextId got one higher)
   if (this.nextId === 65536) {
     this.nextId = 1
diff --git a/lib/store.js b/lib/store.js
index efbfabf09..4f6b1a237 100644
--- a/lib/store.js
+++ b/lib/store.js
@@ -3,11 +3,11 @@
 /**
  * Module dependencies
  */
-var xtend = require('xtend')
+const xtend = require('xtend')
 
-var Readable = require('readable-stream').Readable
-var streamsOpts = { objectMode: true }
-var defaultStoreOptions = {
+const Readable = require('readable-stream').Readable
+const streamsOpts = { objectMode: true }
+const defaultStoreOptions = {
   clean: true
 }
 
@@ -50,10 +50,10 @@ Store.prototype.put = function (packet, cb) {
  *
  */
 Store.prototype.createStream = function () {
-  var stream = new Readable(streamsOpts)
-  var destroyed = false
-  var values = []
-  var i = 0
+  const stream = new Readable(streamsOpts)
+  const values = []
+  let destroyed = false
+  let i = 0
 
   this._inflights.forEach(function (value, key) {
     values.push(value)
@@ -72,7 +72,7 @@ Store.prototype.createStream = function () {
       return
     }
 
-    var self = this
+    const self = this
 
     destroyed = true
 
diff --git a/lib/topic-alias-send.js b/lib/topic-alias-send.js
index f3abf2084..c769d0572 100644
--- a/lib/topic-alias-send.js
+++ b/lib/topic-alias-send.js
@@ -3,8 +3,8 @@
 /**
  * Module dependencies
  */
-var LruMap = require('collections/lru-map')
-var NumberAllocator = require('number-allocator').NumberAllocator
+const LruMap = require('collections/lru-map')
+const NumberAllocator = require('number-allocator').NumberAllocator
 
 /**
  * Topic Alias sending manager
@@ -39,7 +39,7 @@ TopicAliasSend.prototype.put = function (topic, alias) {
   if (entry) {
     delete this.topicToAlias[entry.topic]
   }
-  this.aliasToTopic.set(alias, {'topic': topic, 'alias': alias})
+  this.aliasToTopic.set(alias, { topic: topic, alias: alias })
   this.topicToAlias[topic] = alias
   this.numberAllocator.use(alias)
   this.length = this.aliasToTopic.length
diff --git a/lib/unique-message-id-provider.js b/lib/unique-message-id-provider.js
index 6ffd4bde6..5026253a9 100644
--- a/lib/unique-message-id-provider.js
+++ b/lib/unique-message-id-provider.js
@@ -1,6 +1,6 @@
 'use strict'
 
-var NumberAllocator = require('number-allocator').NumberAllocator
+const NumberAllocator = require('number-allocator').NumberAllocator
 
 /**
  * UniqueMessageAllocator constructor
diff --git a/lib/validations.js b/lib/validations.js
index 1a3277901..ba31e493d 100644
--- a/lib/validations.js
+++ b/lib/validations.js
@@ -10,9 +10,9 @@
  * @returns {Boolean} If the topic is valid, returns true. Otherwise, returns false.
  */
 function validateTopic (topic) {
-  var parts = topic.split('/')
+  const parts = topic.split('/')
 
-  for (var i = 0; i < parts.length; i++) {
+  for (let i = 0; i < parts.length; i++) {
     if (parts[i] === '+') {
       continue
     }
@@ -39,7 +39,7 @@ function validateTopics (topics) {
   if (topics.length === 0) {
     return 'empty_topic_list'
   }
-  for (var i = 0; i < topics.length; i++) {
+  for (let i = 0; i < topics.length; i++) {
     if (!validateTopic(topics[i])) {
       return topics[i]
     }
diff --git a/mqtt.js b/mqtt.js
index c8b94fda1..bdf9389b1 100644
--- a/mqtt.js
+++ b/mqtt.js
@@ -5,11 +5,11 @@
  * See LICENSE for more information
  */
 
-var MqttClient = require('./lib/client')
-var connect = require('./lib/connect')
-var Store = require('./lib/store')
-var DefaultMessageIdProvider = require('./lib/default-message-id-provider')
-var UniqueMessageIdProvider = require('./lib/unique-message-id-provider')
+const MqttClient = require('./lib/client')
+const connect = require('./lib/connect')
+const Store = require('./lib/store')
+const DefaultMessageIdProvider = require('./lib/default-message-id-provider')
+const UniqueMessageIdProvider = require('./lib/unique-message-id-provider')
 
 module.exports.connect = connect
 
diff --git a/package.json b/package.json
index c99fc372f..1848aa0a2 100644
--- a/package.json
+++ b/package.json
@@ -22,7 +22,7 @@
   "main": "mqtt.js",
   "types": "types/index.d.ts",
   "scripts": {
-    "test": "node_modules/.bin/nyc --reporter=lcov --reporter=text ./node_modules/mocha/bin/_mocha",
+    "test": "node_modules/.bin/nyc --reporter=lcov --reporter=text ./node_modules/mocha/bin/_mocha --exit",
     "pretest": "standard | snazzy",
     "tslint": "tslint types/**/*.d.ts",
     "typescript-compile-test": "tsc -p test/typescript/tsconfig.json",
@@ -62,6 +62,7 @@
     "net": false
   },
   "dependencies": {
+    "babel-eslint": "^10.1.0",
     "collections": "^5.1.12",
     "commist": "^1.0.0",
     "concat-stream": "^2.0.0",
@@ -84,14 +85,14 @@
     "@types/node": "^10.0.0",
     "@types/ws": "^7.4.7",
     "aedes": "^0.42.5",
-    "airtap": "^3.0.0",
+    "airtap": "^4.0.4",
     "browserify": "^16.5.0",
     "chai": "^4.2.0",
     "codecov": "^3.0.4",
     "end-of-stream": "^1.4.1",
     "global": "^4.3.2",
     "mkdirp": "^0.5.1",
-    "mocha": "^4.1.0",
+    "mocha": "^9.1.3",
     "mqtt-connection": "^4.0.0",
     "nyc": "^15.0.1",
     "pre-commit": "^1.2.2",
@@ -99,15 +100,25 @@
     "should": "^13.2.1",
     "sinon": "^9.0.0",
     "snazzy": "^8.0.0",
-    "standard": "^11.0.1",
+    "standard": "^16.0.4",
     "tslint": "^5.11.0",
     "tslint-config-standard": "^8.0.1",
     "typescript": "^3.2.2",
     "uglify-es": "^3.3.9"
   },
   "standard": {
+    "parser": "babel-eslint",
     "env": [
       "mocha"
+    ],
+    "globals": [
+      "expect",
+      "test",
+      "describe",
+      "it",
+      "beforeEach",
+      "beforeAll",
+      "afterAll"
     ]
   }
 }
diff --git a/test/abstract_client.js b/test/abstract_client.js
index 4c8b0fa77..bbb54973f 100644
--- a/test/abstract_client.js
+++ b/test/abstract_client.js
@@ -3,17 +3,17 @@
 /**
  * Testing dependencies
  */
-var should = require('chai').should
-var sinon = require('sinon')
-var mqtt = require('../')
-var xtend = require('xtend')
-var Store = require('./../lib/store')
-var assert = require('chai').assert
-var ports = require('./helpers/port_list')
-var serverBuilder = require('./server_helpers_for_client_tests').serverBuilder
+const should = require('chai').should
+const sinon = require('sinon')
+const mqtt = require('../')
+const xtend = require('xtend')
+const Store = require('./../lib/store')
+const assert = require('chai').assert
+const ports = require('./helpers/port_list')
+const serverBuilder = require('./server_helpers_for_client_tests').serverBuilder
 
 module.exports = function (server, config) {
-  var version = config.protocolVersion || 4
+  const version = config.protocolVersion || 4
 
   function connect (opts) {
     opts = xtend(config, opts)
@@ -22,7 +22,7 @@ module.exports = function (server, config) {
 
   describe('closing', function () {
     it('should emit close if stream closes', function (done) {
-      var client = connect()
+      const client = connect()
 
       client.once('connect', function () {
         client.stream.end()
@@ -34,7 +34,7 @@ module.exports = function (server, config) {
     })
 
     it('should mark the client as disconnected', function (done) {
-      var client = connect()
+      const client = connect()
 
       client.once('close', function () {
         client.end()
@@ -50,7 +50,7 @@ module.exports = function (server, config) {
     })
 
     it('should stop ping timer if stream closes', function (done) {
-      var client = connect()
+      const client = connect()
 
       client.once('close', function () {
         assert.notExists(client.pingTimer)
@@ -64,7 +64,7 @@ module.exports = function (server, config) {
     })
 
     it('should emit close after end called', function (done) {
-      var client = connect()
+      const client = connect()
 
       client.once('close', function () {
         done()
@@ -76,7 +76,7 @@ module.exports = function (server, config) {
     })
 
     it('should emit end after end called and client must be disconnected', function (done) {
-      var client = connect()
+      const client = connect()
 
       client.once('end', function () {
         if (client.disconnected) {
@@ -91,8 +91,8 @@ module.exports = function (server, config) {
     })
 
     it('should pass store close error to end callback but not to end listeners (incomingStore)', function (done) {
-      var store = new Store()
-      var client = connect({ incomingStore: store })
+      const store = new Store()
+      const client = connect({ incomingStore: store })
 
       store.close = function (cb) {
         cb(new Error('test'))
@@ -115,8 +115,8 @@ module.exports = function (server, config) {
     })
 
     it('should pass store close error to end callback but not to end listeners (outgoingStore)', function (done) {
-      var store = new Store()
-      var client = connect({ outgoingStore: store })
+      const store = new Store()
+      const client = connect({ outgoingStore: store })
 
       store.close = function (cb) {
         cb(new Error('test'))
@@ -139,11 +139,11 @@ module.exports = function (server, config) {
     })
 
     it('should return `this` if end called twice', function (done) {
-      var client = connect()
+      const client = connect()
 
       client.once('connect', function () {
         client.end()
-        var value = client.end()
+        const value = client.end()
         if (value === client) {
           done()
         } else {
@@ -153,10 +153,10 @@ module.exports = function (server, config) {
     })
 
     it('should emit end only on first client end', function (done) {
-      var client = connect()
+      const client = connect()
 
       client.once('end', function () {
-        var timeout = setTimeout(done.bind(null), 200)
+        const timeout = setTimeout(done.bind(null), 200)
         client.once('end', function () {
           clearTimeout(timeout)
           done(new Error('end was emitted twice'))
@@ -168,7 +168,7 @@ module.exports = function (server, config) {
     })
 
     it('should stop ping timer after end called', function (done) {
-      var client = connect()
+      const client = connect()
 
       client.once('connect', function () {
         assert.exists(client.pingTimer)
@@ -180,9 +180,9 @@ module.exports = function (server, config) {
     })
 
     it('should be able to end even on a failed connection', function (done) {
-      var client = connect({host: 'this_hostname_should_not_exist'})
+      const client = connect({ host: 'this_hostname_should_not_exist' })
 
-      var timeout = setTimeout(function () {
+      const timeout = setTimeout(function () {
         done(new Error('Failed to end a disconnected client'))
       }, 500)
 
@@ -195,9 +195,9 @@ module.exports = function (server, config) {
     })
 
     it('should emit end even on a failed connection', function (done) {
-      var client = connect({host: 'this_hostname_should_not_exist'})
+      const client = connect({ host: 'this_hostname_should_not_exist' })
 
-      var timeout = setTimeout(function () {
+      const timeout = setTimeout(function () {
         done(new Error('Disconnected client has failed to emit end'))
       }, 500)
 
@@ -208,7 +208,7 @@ module.exports = function (server, config) {
 
       // after 200ms manually invoke client.end
       setTimeout(() => {
-        var boundEnd = client.end.bind(client)
+        const boundEnd = client.end.bind(client)
         boundEnd()
       }, 200)
     })
@@ -218,13 +218,13 @@ module.exports = function (server, config) {
       // Reason for it is that there are overlaps in the reconnectTimer and connectTimer. In the PR for this code
       // there will be gists showing the difference between a successful test here and a failed test. For now we
       // will add the retries syntax because of the flakiness.
-      var client = connect({host: 'this_hostname_should_not_exist', connectTimeout: 10, reconnectPeriod: 20})
+      const client = connect({ host: 'this_hostname_should_not_exist', connectTimeout: 10, reconnectPeriod: 20 })
       setTimeout(done.bind(null), 1000)
-      var endCallback = function () {
+      const endCallback = function () {
         assert.strictEqual(spy.callCount, 1, 'end was emitted more than once for reconnecting client')
       }
 
-      var spy = sinon.spy(endCallback)
+      const spy = sinon.spy(endCallback)
       client.on('end', spy)
       setTimeout(() => {
         client.end.bind(client)
@@ -235,7 +235,7 @@ module.exports = function (server, config) {
 
   describe('connecting', function () {
     it('should connect to the broker', function (done) {
-      var client = connect()
+      const client = connect()
       client.on('error', done)
 
       server.once('client', function () {
@@ -245,7 +245,7 @@ module.exports = function (server, config) {
     })
 
     it('should send a default client id', function (done) {
-      var client = connect()
+      const client = connect()
       client.on('error', done)
 
       server.once('client', function (serverClient) {
@@ -258,7 +258,7 @@ module.exports = function (server, config) {
     })
 
     it('should send be clean by default', function (done) {
-      var client = connect()
+      const client = connect()
       client.on('error', done)
 
       server.once('client', function (serverClient) {
@@ -271,7 +271,7 @@ module.exports = function (server, config) {
     })
 
     it('should connect with the given client id', function (done) {
-      var client = connect({clientId: 'testclient'})
+      const client = connect({ clientId: 'testclient' })
       client.on('error', function (err) {
         throw err
       })
@@ -288,7 +288,7 @@ module.exports = function (server, config) {
     })
 
     it('should connect with the client id and unclean state', function (done) {
-      var client = connect({clientId: 'testclient', clean: false})
+      const client = connect({ clientId: 'testclient', clean: false })
       client.on('error', function (err) {
         throw err
       })
@@ -307,7 +307,7 @@ module.exports = function (server, config) {
 
     it('should require a clientId with clean=false', function (done) {
       try {
-        var client = connect({ clean: false })
+        const client = connect({ clean: false })
         client.on('error', function (err) {
           done(err)
         })
@@ -318,7 +318,7 @@ module.exports = function (server, config) {
     })
 
     it('should default to localhost', function (done) {
-      var client = connect({clientId: 'testclient'})
+      const client = connect({ clientId: 'testclient' })
       client.on('error', function (err) {
         throw err
       })
@@ -333,7 +333,7 @@ module.exports = function (server, config) {
     })
 
     it('should emit connect', function (done) {
-      var client = connect()
+      const client = connect()
       client.once('connect', function () {
         client.end(true, done)
       })
@@ -341,7 +341,7 @@ module.exports = function (server, config) {
     })
 
     it('should provide connack packet with connect event', function (done) {
-      var connack = version === 5 ? {reasonCode: 0} : {returnCode: 0}
+      const connack = version === 5 ? { reasonCode: 0 } : { returnCode: 0 }
       server.once('client', function (serverClient) {
         connack.sessionPresent = true
         serverClient.connack(connack)
@@ -351,7 +351,7 @@ module.exports = function (server, config) {
         })
       })
 
-      var client = connect()
+      const client = connect()
       client.once('connect', function (packet) {
         assert.strictEqual(packet.sessionPresent, true)
         client.once('connect', function (packet) {
@@ -363,7 +363,7 @@ module.exports = function (server, config) {
     })
 
     it('should mark the client as connected', function (done) {
-      var client = connect()
+      const client = connect()
       client.once('connect', function () {
         client.end()
         if (client.connected) {
@@ -375,12 +375,12 @@ module.exports = function (server, config) {
     })
 
     it('should emit error on invalid clientId', function (done) {
-      var client = connect({clientId: 'invalid'})
+      const client = connect({ clientId: 'invalid' })
       client.once('connect', function () {
         done(new Error('Should not emit connect'))
       })
       client.once('error', function (error) {
-        var value = version === 5 ? 128 : 2
+        const value = version === 5 ? 128 : 2
         assert.strictEqual(error.code, value) // code for clientID identifer rejected
         client.end()
         done()
@@ -389,7 +389,7 @@ module.exports = function (server, config) {
 
     it('should emit error event if the socket refuses the connection', function (done) {
       // fake a port
-      var client = connect({ port: 4557 })
+      const client = connect({ port: 4557 })
 
       client.on('error', function (e) {
         assert.equal(e.code, 'ECONNREFUSED')
@@ -403,8 +403,8 @@ module.exports = function (server, config) {
       // method completes closing the stores and invokes the callback, and another time when the
       // stream is closed. When the stream is closed, for some reason the closeStores method is called
       // a second time.
-      var client1 = connect()
-      var client2 = connect()
+      const client1 = connect()
+      const client2 = connect()
 
       assert.notStrictEqual(client1.options.clientId, client2.options.clientId)
       client1.end(true, () => {
@@ -417,7 +417,7 @@ module.exports = function (server, config) {
 
   describe('handling offline states', function () {
     it('should emit offline event once when the client transitions from connected states to disconnected ones', function (done) {
-      var client = connect({reconnectPeriod: 20})
+      const client = connect({ reconnectPeriod: 20 })
 
       client.on('connect', function () {
         this.stream.end()
@@ -430,7 +430,7 @@ module.exports = function (server, config) {
 
     it('should emit offline event once when the client (at first) can NOT connect to servers', function (done) {
       // fake a port
-      var client = connect({ reconnectPeriod: 20, port: 4557 })
+      const client = connect({ reconnectPeriod: 20, port: 4557 })
 
       client.on('error', function () {})
 
@@ -442,7 +442,7 @@ module.exports = function (server, config) {
 
   describe('topic validations when subscribing', function () {
     it('should be ok for well-formated topics', function (done) {
-      var client = connect()
+      const client = connect()
       client.subscribe(
         [
           '+', '+/event', 'event/+', '#', 'event/#', 'system/event/+',
@@ -461,7 +461,7 @@ module.exports = function (server, config) {
     })
 
     it('should return an error (via callbacks) for topic #/event', function (done) {
-      var client = connect()
+      const client = connect()
       client.subscribe(['#/event', 'event#', 'event+'], function (err) {
         client.end(false, function () {
           if (err) {
@@ -473,7 +473,7 @@ module.exports = function (server, config) {
     })
 
     it('should return an empty array for duplicate subs', function (done) {
-      var client = connect()
+      const client = connect()
       client.subscribe('event', function (err, granted1) {
         if (err) {
           return done(err)
@@ -490,7 +490,7 @@ module.exports = function (server, config) {
     })
 
     it('should return an error (via callbacks) for topic #/event', function (done) {
-      var client = connect()
+      const client = connect()
       client.subscribe('#/event', function (err) {
         client.end(function () {
           if (err) {
@@ -502,7 +502,7 @@ module.exports = function (server, config) {
     })
 
     it('should return an error (via callbacks) for topic event#', function (done) {
-      var client = connect()
+      const client = connect()
       client.subscribe('event#', function (err) {
         client.end(function () {
           if (err) {
@@ -514,7 +514,7 @@ module.exports = function (server, config) {
     })
 
     it('should return an error (via callbacks) for topic system/#/event', function (done) {
-      var client = connect()
+      const client = connect()
       client.subscribe('system/#/event', function (err) {
         client.end(function () {
           if (err) {
@@ -526,7 +526,7 @@ module.exports = function (server, config) {
     })
 
     it('should return an error (via callbacks) for empty topic list', function (done) {
-      var client = connect()
+      const client = connect()
       client.subscribe([], function (err) {
         client.end()
         if (err) {
@@ -537,7 +537,7 @@ module.exports = function (server, config) {
     })
 
     it('should return an error (via callbacks) for topic system/+/#/event', function (done) {
-      var client = connect()
+      const client = connect()
       client.subscribe('system/+/#/event', function (err) {
         client.end(true, function () {
           if (err) {
@@ -551,7 +551,7 @@ module.exports = function (server, config) {
 
   describe('offline messages', function () {
     it('should queue message until connected', function (done) {
-      var client = connect()
+      const client = connect()
 
       client.publish('test', 'test')
       client.subscribe('test')
@@ -567,9 +567,9 @@ module.exports = function (server, config) {
     })
 
     it('should not queue qos 0 messages if queueQoSZero is false', function (done) {
-      var client = connect({queueQoSZero: false})
+      const client = connect({ queueQoSZero: false })
 
-      client.publish('test', 'test', {qos: 0})
+      client.publish('test', 'test', { qos: 0 })
       assert.strictEqual(client.queue.length, 0)
       client.on('connect', function () {
         setTimeout(function () {
@@ -579,10 +579,10 @@ module.exports = function (server, config) {
     })
 
     it('should queue qos != 0 messages', function (done) {
-      var client = connect({queueQoSZero: false})
+      const client = connect({ queueQoSZero: false })
 
-      client.publish('test', 'test', {qos: 1})
-      client.publish('test', 'test', {qos: 2})
+      client.publish('test', 'test', { qos: 1 })
+      client.publish('test', 'test', { qos: 2 })
       client.subscribe('test')
       client.unsubscribe('test')
       assert.strictEqual(client.queue.length, 2)
@@ -594,18 +594,18 @@ module.exports = function (server, config) {
     })
 
     it('should not interrupt messages', function (done) {
-      var client = null
-      var incomingStore = new mqtt.Store({ clean: false })
-      var outgoingStore = new mqtt.Store({ clean: false })
-      var publishCount = 0
-      var server2 = serverBuilder(config.protocol, function (serverClient) {
+      let client = null
+      let publishCount = 0
+      const incomingStore = new mqtt.Store({ clean: false })
+      const outgoingStore = new mqtt.Store({ clean: false })
+      const server2 = serverBuilder(config.protocol, function (serverClient) {
         serverClient.on('connect', function () {
-          var connack = version === 5 ? { reasonCode: 0 } : { returnCode: 0 }
+          const connack = version === 5 ? { reasonCode: 0 } : { returnCode: 0 }
           serverClient.connack(connack)
         })
         serverClient.on('publish', function (packet) {
           if (packet.qos !== 0) {
-            serverClient.puback({messageId: packet.messageId})
+            serverClient.puback({ messageId: packet.messageId })
           }
           switch (publishCount++) {
             case 0:
@@ -641,22 +641,22 @@ module.exports = function (server, config) {
           if (packet.cmd === 'connack') {
             setImmediate(
               function () {
-                client.publish('test', 'payload3', {qos: 1})
-                client.publish('test', 'payload4', {qos: 0})
+                client.publish('test', 'payload3', { qos: 1 })
+                client.publish('test', 'payload4', { qos: 0 })
               }
             )
           }
         })
-        client.publish('test', 'payload1', {qos: 2})
-        client.publish('test', 'payload2', {qos: 2})
+        client.publish('test', 'payload1', { qos: 2 })
+        client.publish('test', 'payload2', { qos: 2 })
       })
     })
 
     it('should call cb if an outgoing QoS 0 message is not sent', function (done) {
-      var client = connect({queueQoSZero: false})
-      var called = false
+      const client = connect({ queueQoSZero: false })
+      let called = false
 
-      client.publish('test', 'test', {qos: 0}, function () {
+      client.publish('test', 'test', { qos: 0 }, function () {
         called = true
       })
 
@@ -669,8 +669,8 @@ module.exports = function (server, config) {
     })
 
     it('should delay ending up until all inflight messages are delivered', function (done) {
-      var client = connect()
-      var subscribeCalled = false
+      const client = connect()
+      let subscribeCalled = false
 
       client.on('connect', function () {
         client.subscribe('test', function () {
@@ -686,8 +686,8 @@ module.exports = function (server, config) {
     })
 
     it('wait QoS 1 publish messages', function (done) {
-      var client = connect()
-      var messageReceived = false
+      const client = connect()
+      let messageReceived = false
 
       client.on('connect', function () {
         client.subscribe('test')
@@ -713,7 +713,7 @@ module.exports = function (server, config) {
 
     it('does not wait acks when force-closing', function (done) {
       // non-running broker
-      var client = connect('mqtt://localhost:8993')
+      const client = connect('mqtt://localhost:8993')
       client.publish('test', 'test', { qos: 1 })
       client.end(true, done)
     })
@@ -723,7 +723,7 @@ module.exports = function (server, config) {
       store.put = function (packet, cb) {
         process.nextTick(cb, new Error('oops there is an error'))
       }
-      var client = connect({ incomingStore: store, outgoingStore: store })
+      const client = connect({ incomingStore: store, outgoingStore: store })
       client.publish('test', 'test', { qos: 2 }, function (err) {
         if (err) {
           client.end(true, done)
@@ -734,9 +734,9 @@ module.exports = function (server, config) {
 
   describe('publishing', function () {
     it('should publish a message (offline)', function (done) {
-      var client = connect()
-      var payload = 'test'
-      var topic = 'test'
+      const client = connect()
+      const payload = 'test'
+      const topic = 'test'
       // don't wait on connect to send publish
       client.publish(topic, payload)
 
@@ -758,9 +758,9 @@ module.exports = function (server, config) {
     })
 
     it('should publish a message (online)', function (done) {
-      var client = connect()
-      var payload = 'test'
-      var topic = 'test'
+      const client = connect()
+      const payload = 'test'
+      const topic = 'test'
       // block on connect before sending publish
       client.on('connect', function () {
         client.publish(topic, payload)
@@ -784,10 +784,10 @@ module.exports = function (server, config) {
     })
 
     it('should publish a message (retain, offline)', function (done) {
-      var client = connect({ queueQoSZero: true })
-      var payload = 'test'
-      var topic = 'test'
-      var called = false
+      const client = connect({ queueQoSZero: true })
+      const payload = 'test'
+      const topic = 'test'
+      let called = false
 
       client.publish(topic, payload, { retain: true }, function () {
         called = true
@@ -806,9 +806,9 @@ module.exports = function (server, config) {
     })
 
     it('should emit a packetsend event', function (done) {
-      var client = connect()
-      var payload = 'test_payload'
-      var topic = 'testTopic'
+      const client = connect()
+      const payload = 'test_payload'
+      const topic = 'testTopic'
 
       client.on('packetsend', function (packet) {
         if (packet.cmd === 'publish') {
@@ -826,10 +826,10 @@ module.exports = function (server, config) {
     })
 
     it('should accept options', function (done) {
-      var client = connect()
-      var payload = 'test'
-      var topic = 'test'
-      var opts = {
+      const client = connect()
+      const payload = 'test'
+      const topic = 'test'
+      const opts = {
         retain: true,
         qos: 1
       }
@@ -851,10 +851,10 @@ module.exports = function (server, config) {
     })
 
     it('should publish with the default options for an empty parameter', function (done) {
-      var client = connect()
-      var payload = 'test'
-      var topic = 'test'
-      var defaultOpts = {qos: 0, retain: false, dup: false}
+      const client = connect()
+      const payload = 'test'
+      const topic = 'test'
+      const defaultOpts = { qos: 0, retain: false, dup: false }
 
       client.once('connect', function () {
         client.publish(topic, payload, {})
@@ -873,10 +873,10 @@ module.exports = function (server, config) {
     })
 
     it('should mark a message as  duplicate when "dup" option is set', function (done) {
-      var client = connect()
-      var payload = 'duplicated-test'
-      var topic = 'test'
-      var opts = {
+      const client = connect()
+      const payload = 'duplicated-test'
+      const topic = 'test'
+      const opts = {
         retain: true,
         qos: 1,
         dup: true
@@ -899,7 +899,7 @@ module.exports = function (server, config) {
     })
 
     it('should fire a callback (qos 0)', function (done) {
-      var client = connect()
+      const client = connect()
 
       client.once('connect', function () {
         client.publish('a', 'b', function () {
@@ -910,8 +910,8 @@ module.exports = function (server, config) {
     })
 
     it('should fire a callback (qos 1)', function (done) {
-      var client = connect()
-      var opts = { qos: 1 }
+      const client = connect()
+      const opts = { qos: 1 }
 
       client.once('connect', function () {
         client.publish('a', 'b', opts, function () {
@@ -922,8 +922,8 @@ module.exports = function (server, config) {
     })
 
     it('should fire a callback (qos 2)', function (done) {
-      var client = connect()
-      var opts = { qos: 2 }
+      const client = connect()
+      const opts = { qos: 2 }
 
       client.once('connect', function () {
         client.publish('a', 'b', opts, function () {
@@ -934,7 +934,7 @@ module.exports = function (server, config) {
     })
 
     it('should support UTF-8 characters in topic', function (done) {
-      var client = connect()
+      const client = connect()
 
       client.once('connect', function () {
         client.publish('中国', 'hello', function () {
@@ -945,7 +945,7 @@ module.exports = function (server, config) {
     })
 
     it('should support UTF-8 characters in payload', function (done) {
-      var client = connect()
+      const client = connect()
 
       client.once('connect', function () {
         client.publish('hello', '中国', function () {
@@ -956,8 +956,8 @@ module.exports = function (server, config) {
     })
 
     it('should publish 10 QoS 2 and receive them', function (done) {
-      var client = connect()
-      var count = 0
+      const client = connect()
+      let count = 0
 
       client.on('connect', function () {
         client.subscribe('test')
@@ -992,10 +992,10 @@ module.exports = function (server, config) {
     })
 
     function testQosHandleMessage (qos, done) {
-      var client = connect()
+      const client = connect()
 
-      var messageEventCount = 0
-      var handleMessageCount = 0
+      let messageEventCount = 0
+      let handleMessageCount = 0
 
       client.handleMessage = function (packet, callback) {
         setTimeout(function () {
@@ -1027,7 +1027,7 @@ module.exports = function (server, config) {
         })
 
         serverClient.on('subscribe', function () {
-          for (var i = 0; i < 10; i++) {
+          for (let i = 0; i < 10; i++) {
             serverClient.publish({
               messageId: i,
               topic: 'test',
@@ -1039,7 +1039,7 @@ module.exports = function (server, config) {
       })
     }
 
-    var qosTests = [ 0, 1, 2 ]
+    const qosTests = [0, 1, 2]
     qosTests.forEach(function (QoS) {
       it('should publish 10 QoS ' + QoS + 'and receive them only when `handleMessage` finishes', function (done) {
         testQosHandleMessage(QoS, done)
@@ -1047,7 +1047,7 @@ module.exports = function (server, config) {
     })
 
     it('should not send a `puback` if the execution of `handleMessage` fails for messages with QoS `1`', function (done) {
-      var client = connect()
+      const client = connect()
 
       client.handleMessage = function (packet, callback) {
         callback(new Error('Error thrown by the application'))
@@ -1071,7 +1071,7 @@ module.exports = function (server, config) {
 
     it('should silently ignore errors thrown by `handleMessage` and return when no callback is passed ' +
       'into `handlePublish` method', function (done) {
-      var client = connect()
+      const client = connect()
 
       client.handleMessage = function (packet, callback) {
         callback(new Error('Error thrown by the application'))
@@ -1103,8 +1103,8 @@ module.exports = function (server, config) {
         }
       }
 
-      var store = new AsyncStore()
-      var client = connect({incomingStore: store})
+      const store = new AsyncStore()
+      const client = connect({ incomingStore: store })
 
       client._handlePublish({
         messageId: 1,
@@ -1118,6 +1118,9 @@ module.exports = function (server, config) {
     })
 
     it('should handle error with async incoming store in QoS 2 `handlePublish` method', function (done) {
+      const timeout = setTimeout(() => {
+        done('test timed out')
+      }, 10000)
       class AsyncStore {
         put (packet, cb) {
           process.nextTick(function () {
@@ -1125,13 +1128,25 @@ module.exports = function (server, config) {
           })
         }
 
+        del (packet, cb) {
+          process.nextTick(function () {
+            cb(new Error('Error'))
+          })
+        }
+
+        get (packet, cb) {
+          process.nextTick(function () {
+            cb(null, { cmd: 'publish' })
+          })
+        }
+
         close (cb) {
           cb()
         }
       }
 
-      var store = new AsyncStore()
-      var client = connect({incomingStore: store})
+      const store = new AsyncStore()
+      const client = connect({ incomingStore: store })
 
       client._handlePublish({
         messageId: 1,
@@ -1140,6 +1155,7 @@ module.exports = function (server, config) {
         qos: 2
       }, function () {
         client.end()
+        clearTimeout(timeout)
         done()
       })
     })
@@ -1160,7 +1176,7 @@ module.exports = function (server, config) {
 
         get (packet, cb) {
           process.nextTick(function () {
-            cb(null, {cmd: 'publish'})
+            cb(null, { cmd: 'publish' })
           })
         }
 
@@ -1169,8 +1185,8 @@ module.exports = function (server, config) {
         }
       }
 
-      var store = new AsyncStore()
-      var client = connect({ incomingStore: store })
+      const store = new AsyncStore()
+      const client = connect({ incomingStore: store })
 
       client._handlePubrel({
         messageId: 1,
@@ -1181,7 +1197,7 @@ module.exports = function (server, config) {
     })
 
     it('should handle success with async incoming store in QoS 2 `handlePubrel` method', function (done) {
-      var delComplete = false
+      let delComplete = false
       class AsyncStore {
         put (packet, cb) {
           process.nextTick(function () {
@@ -1198,7 +1214,7 @@ module.exports = function (server, config) {
 
         get (packet, cb) {
           process.nextTick(function () {
-            cb(null, {cmd: 'publish'})
+            cb(null, { cmd: 'publish' })
           })
         }
 
@@ -1207,8 +1223,8 @@ module.exports = function (server, config) {
         }
       }
 
-      var store = new AsyncStore()
-      var client = connect({incomingStore: store})
+      const store = new AsyncStore()
+      const client = connect({ incomingStore: store })
 
       client._handlePubrel({
         messageId: 1,
@@ -1220,20 +1236,20 @@ module.exports = function (server, config) {
     })
 
     it('should not send a `pubcomp` if the execution of `handleMessage` fails for messages with QoS `2`', function (done) {
-      var store = new Store()
-      var client = connect({incomingStore: store})
+      const store = new Store()
+      const client = connect({ incomingStore: store })
 
-      var messageId = Math.floor(65535 * Math.random())
-      var topic = 'testTopic'
-      var payload = 'testPayload'
-      var qos = 2
+      const messageId = Math.floor(65535 * Math.random())
+      const topic = 'testTopic'
+      const payload = 'testPayload'
+      const qos = 2
 
       client.handleMessage = function (packet, callback) {
         callback(new Error('Error thrown by the application'))
       }
 
       client.once('connect', function () {
-        client.subscribe(topic, {qos: 2})
+        client.subscribe(topic, { qos: 2 })
 
         store.put({
           messageId: messageId,
@@ -1244,7 +1260,7 @@ module.exports = function (server, config) {
         }, function () {
           // cleans up the client
           client._sendPacket = sinon.spy()
-          client._handlePubrel({cmd: 'pubrel', messageId: messageId}, function (err) {
+          client._handlePubrel({ cmd: 'pubrel', messageId: messageId }, function (err) {
             assert.exists(err)
             assert.strictEqual(client._sendPacket.callCount, 0)
             client.end(true, done)
@@ -1255,20 +1271,20 @@ module.exports = function (server, config) {
 
     it('should silently ignore errors thrown by `handleMessage` and return when no callback is passed ' +
       'into `handlePubrel` method', function (done) {
-      var store = new Store()
-      var client = connect({incomingStore: store})
+      const store = new Store()
+      const client = connect({ incomingStore: store })
 
-      var messageId = Math.floor(65535 * Math.random())
-      var topic = 'test'
-      var payload = 'test'
-      var qos = 2
+      const messageId = Math.floor(65535 * Math.random())
+      const topic = 'test'
+      const payload = 'test'
+      const qos = 2
 
       client.handleMessage = function (packet, callback) {
         callback(new Error('Error thrown by the application'))
       }
 
       client.once('connect', function () {
-        client.subscribe(topic, {qos: 2})
+        client.subscribe(topic, { qos: 2 })
 
         store.put({
           messageId: messageId,
@@ -1278,7 +1294,7 @@ module.exports = function (server, config) {
           cmd: 'publish'
         }, function () {
           try {
-            client._handlePubrel({cmd: 'pubrel', messageId: messageId})
+            client._handlePubrel({ cmd: 'pubrel', messageId: messageId })
             client.end(true, done)
           } catch (err) {
             client.end(true, () => { done(err) })
@@ -1288,22 +1304,22 @@ module.exports = function (server, config) {
     })
 
     it('should keep message order', function (done) {
-      var publishCount = 0
-      var reconnect = false
-      var client = {}
-      var incomingStore = new mqtt.Store({ clean: false })
-      var outgoingStore = new mqtt.Store({ clean: false })
-      var server2 = serverBuilder(config.protocol, function (serverClient) {
+      let publishCount = 0
+      let reconnect = false
+      let client = {}
+      const incomingStore = new mqtt.Store({ clean: false })
+      const outgoingStore = new mqtt.Store({ clean: false })
+      const server2 = serverBuilder(config.protocol, function (serverClient) {
         // errors are not interesting for this test
         // but they might happen on some platforms
         serverClient.on('error', function () {})
 
         serverClient.on('connect', function (packet) {
-          var connack = version === 5 ? { reasonCode: 0 } : { returnCode: 0 }
+          const connack = version === 5 ? { reasonCode: 0 } : { returnCode: 0 }
           serverClient.connack(connack)
         })
         serverClient.on('publish', function (packet) {
-          serverClient.puback({messageId: packet.messageId})
+          serverClient.puback({ messageId: packet.messageId })
           if (reconnect) {
             switch (publishCount++) {
               case 0:
@@ -1335,11 +1351,11 @@ module.exports = function (server, config) {
 
         client.on('connect', function () {
           if (!reconnect) {
-            client.publish('topic', 'payload1', {qos: 1})
-            client.publish('topic', 'payload2', {qos: 1})
+            client.publish('topic', 'payload1', { qos: 1 })
+            client.publish('topic', 'payload2', { qos: 1 })
             client.end(true)
           } else {
-            client.publish('topic', 'payload3', {qos: 1})
+            client.publish('topic', 'payload3', { qos: 1 })
           }
         })
         client.on('close', function () {
@@ -1356,19 +1372,19 @@ module.exports = function (server, config) {
     })
 
     function testCallbackStorePutByQoS (qos, clean, expected, done) {
-      var client = connect({
+      const client = connect({
         clean: clean,
         clientId: 'testId'
       })
 
-      var callbacks = []
+      const callbacks = []
 
       function cbStorePut () {
         callbacks.push('storeput')
       }
 
       client.on('connect', function () {
-        client.publish('test', 'test', {qos: qos, cbStorePut: cbStorePut}, function (err) {
+        client.publish('test', 'test', { qos: qos, cbStorePut: cbStorePut }, function (err) {
           if (err) done(err)
           callbacks.push('publish')
           assert.deepEqual(callbacks, expected)
@@ -1377,13 +1393,13 @@ module.exports = function (server, config) {
       })
     }
 
-    var callbackStorePutByQoSParameters = [
-      {args: [0, true], expected: ['publish']},
-      {args: [0, false], expected: ['publish']},
-      {args: [1, true], expected: ['storeput', 'publish']},
-      {args: [1, false], expected: ['storeput', 'publish']},
-      {args: [2, true], expected: ['storeput', 'publish']},
-      {args: [2, false], expected: ['storeput', 'publish']}
+    const callbackStorePutByQoSParameters = [
+      { args: [0, true], expected: ['publish'] },
+      { args: [0, false], expected: ['publish'] },
+      { args: [1, true], expected: ['storeput', 'publish'] },
+      { args: [1, false], expected: ['storeput', 'publish'] },
+      { args: [2, true], expected: ['storeput', 'publish'] },
+      { args: [2, false], expected: ['storeput', 'publish'] }
     ]
 
     callbackStorePutByQoSParameters.forEach(function (test) {
@@ -1401,7 +1417,7 @@ module.exports = function (server, config) {
 
   describe('unsubscribing', function () {
     it('should send an unsubscribe packet (offline)', function (done) {
-      var client = connect()
+      const client = connect()
 
       client.unsubscribe('test')
 
@@ -1414,8 +1430,8 @@ module.exports = function (server, config) {
     })
 
     it('should send an unsubscribe packet', function (done) {
-      var client = connect()
-      var topic = 'topic'
+      const client = connect()
+      const topic = 'topic'
 
       client.once('connect', function () {
         client.unsubscribe(topic)
@@ -1430,8 +1446,8 @@ module.exports = function (server, config) {
     })
 
     it('should emit a packetsend event', function (done) {
-      var client = connect()
-      var testTopic = 'testTopic'
+      const client = connect()
+      const testTopic = 'testTopic'
 
       client.once('connect', function () {
         client.subscribe(testTopic)
@@ -1445,8 +1461,8 @@ module.exports = function (server, config) {
     })
 
     it('should emit a packetreceive event', function (done) {
-      var client = connect()
-      var testTopic = 'testTopic'
+      const client = connect()
+      const testTopic = 'testTopic'
 
       client.once('connect', function () {
         client.subscribe(testTopic)
@@ -1460,8 +1476,8 @@ module.exports = function (server, config) {
     })
 
     it('should accept an array of unsubs', function (done) {
-      var client = connect()
-      var topics = ['topic1', 'topic2']
+      const client = connect()
+      const topics = ['topic1', 'topic2']
 
       client.once('connect', function () {
         client.unsubscribe(topics)
@@ -1476,8 +1492,8 @@ module.exports = function (server, config) {
     })
 
     it('should fire a callback on unsuback', function (done) {
-      var client = connect()
-      var topic = 'topic'
+      const client = connect()
+      const topic = 'topic'
 
       client.once('connect', function () {
         client.unsubscribe(topic, () => {
@@ -1493,8 +1509,8 @@ module.exports = function (server, config) {
     })
 
     it('should unsubscribe from a chinese topic', function (done) {
-      var client = connect()
-      var topic = '中国'
+      const client = connect()
+      const topic = '中国'
 
       client.once('connect', function () {
         client.unsubscribe(topic, () => {
@@ -1513,8 +1529,9 @@ module.exports = function (server, config) {
   })
 
   describe('keepalive', function () {
-    var clock
+    let clock
 
+    // eslint-disable-next-line
     beforeEach(function () {
       clock = sinon.useFakeTimers()
     })
@@ -1524,8 +1541,8 @@ module.exports = function (server, config) {
     })
 
     it('should checkPing at keepalive interval', function (done) {
-      var interval = 3
-      var client = connect({ keepalive: interval })
+      const interval = 3
+      const client = connect({ keepalive: interval })
 
       client._checkPing = sinon.spy()
 
@@ -1544,8 +1561,8 @@ module.exports = function (server, config) {
     })
 
     it('should not checkPing if publishing at a higher rate than keepalive', function (done) {
-      var intervalMs = 3000
-      var client = connect({keepalive: intervalMs / 1000})
+      const intervalMs = 3000
+      const client = connect({ keepalive: intervalMs / 1000 })
 
       client._checkPing = sinon.spy()
 
@@ -1561,8 +1578,8 @@ module.exports = function (server, config) {
     })
 
     it('should checkPing if publishing at a higher rate than keepalive and reschedulePings===false', function (done) {
-      var intervalMs = 3000
-      var client = connect({
+      const intervalMs = 3000
+      const client = connect({
         keepalive: intervalMs / 1000,
         reschedulePings: false
       })
@@ -1583,7 +1600,7 @@ module.exports = function (server, config) {
 
   describe('pinging', function () {
     it('should set a ping timer', function (done) {
-      var client = connect({keepalive: 3})
+      const client = connect({ keepalive: 3 })
       client.once('connect', function () {
         assert.exists(client.pingTimer)
         client.end(true, done)
@@ -1591,7 +1608,7 @@ module.exports = function (server, config) {
     })
 
     it('should not set a ping timer keepalive=0', function (done) {
-      var client = connect({keepalive: 0})
+      const client = connect({ keepalive: 0 })
       client.on('connect', function () {
         assert.notExists(client.pingTimer)
         client.end(true, done)
@@ -1599,7 +1616,8 @@ module.exports = function (server, config) {
     })
 
     it('should reconnect if pingresp is not sent', function (done) {
-      var client = connect({keepalive: 1, reconnectPeriod: 100})
+      this.timeout(4000)
+      const client = connect({ keepalive: 1, reconnectPeriod: 100 })
 
       // Fake no pingresp being send by stubbing the _handlePingresp function
       client._handlePingresp = function () {}
@@ -1612,7 +1630,7 @@ module.exports = function (server, config) {
     })
 
     it('should not reconnect if pingresp is successful', function (done) {
-      var client = connect({keepalive: 100})
+      const client = connect({ keepalive: 100 })
       client.once('close', function () {
         done(new Error('Client closed connection'))
       })
@@ -1620,7 +1638,7 @@ module.exports = function (server, config) {
     })
 
     it('should defer the next ping when sending a control packet', function (done) {
-      var client = connect({keepalive: 1})
+      const client = connect({ keepalive: 1 })
 
       client.once('connect', function () {
         client._checkPing = sinon.spy()
@@ -1646,7 +1664,7 @@ module.exports = function (server, config) {
 
   describe('subscribing', function () {
     it('should send a subscribe message (offline)', function (done) {
-      var client = connect()
+      const client = connect()
 
       client.subscribe('test')
 
@@ -1658,8 +1676,8 @@ module.exports = function (server, config) {
     })
 
     it('should send a subscribe message', function (done) {
-      var client = connect()
-      var topic = 'test'
+      const client = connect()
+      const topic = 'test'
 
       client.once('connect', function () {
         client.subscribe(topic)
@@ -1667,7 +1685,7 @@ module.exports = function (server, config) {
 
       server.once('client', function (serverClient) {
         serverClient.once('subscribe', function (packet) {
-          var result = {
+          const result = {
             topic: topic,
             qos: 0
           }
@@ -1683,8 +1701,8 @@ module.exports = function (server, config) {
     })
 
     it('should emit a packetsend event', function (done) {
-      var client = connect()
-      var testTopic = 'testTopic'
+      const client = connect()
+      const testTopic = 'testTopic'
 
       client.once('connect', function () {
         client.subscribe(testTopic)
@@ -1698,8 +1716,8 @@ module.exports = function (server, config) {
     })
 
     it('should emit a packetreceive event', function (done) {
-      var client = connect()
-      var testTopic = 'testTopic'
+      const client = connect()
+      const testTopic = 'testTopic'
 
       client.once('connect', function () {
         client.subscribe(testTopic)
@@ -1713,8 +1731,8 @@ module.exports = function (server, config) {
     })
 
     it('should accept an array of subscriptions', function (done) {
-      var client = connect()
-      var subs = ['test1', 'test2']
+      const client = connect()
+      const subs = ['test1', 'test2']
 
       client.once('connect', function () {
         client.subscribe(subs)
@@ -1723,8 +1741,8 @@ module.exports = function (server, config) {
       server.once('client', function (serverClient) {
         serverClient.once('subscribe', function (packet) {
           // i.e. [{topic: 'a', qos: 0}, {topic: 'b', qos: 0}]
-          var expected = subs.map(function (i) {
-            var result = {topic: i, qos: 0}
+          const expected = subs.map(function (i) {
+            const result = { topic: i, qos: 0 }
             if (version === 5) {
               result.nl = false
               result.rap = false
@@ -1740,10 +1758,10 @@ module.exports = function (server, config) {
     })
 
     it('should accept a hash of subscriptions', function (done) {
-      var client = connect()
-      var topics = {
-        test1: {qos: 0},
-        test2: {qos: 1}
+      const client = connect()
+      const topics = {
+        test1: { qos: 0 },
+        test2: { qos: 1 }
       }
 
       client.once('connect', function () {
@@ -1752,12 +1770,11 @@ module.exports = function (server, config) {
 
       server.once('client', function (serverClient) {
         serverClient.once('subscribe', function (packet) {
-          var k
-          var expected = []
+          const expected = []
 
-          for (k in topics) {
-            if (topics.hasOwnProperty(k)) {
-              var result = {
+          for (const k in topics) {
+            if (Object.prototype.hasOwnProperty.call(topics, k)) {
+              const result = {
                 topic: k,
                 qos: topics[k].qos
               }
@@ -1777,9 +1794,9 @@ module.exports = function (server, config) {
     })
 
     it('should accept an options parameter', function (done) {
-      var client = connect()
-      var topic = 'test'
-      var opts = {qos: 1}
+      const client = connect()
+      const topic = 'test'
+      const opts = { qos: 1 }
 
       client.once('connect', function () {
         client.subscribe(topic, opts)
@@ -1787,7 +1804,7 @@ module.exports = function (server, config) {
 
       server.once('client', function (serverClient) {
         serverClient.once('subscribe', function (packet) {
-          var expected = [{
+          const expected = [{
             topic: topic,
             qos: 1
           }]
@@ -1805,9 +1822,9 @@ module.exports = function (server, config) {
     })
 
     it('should subscribe with the default options for an empty options parameter', function (done) {
-      var client = connect()
-      var topic = 'test'
-      var defaultOpts = {qos: 0}
+      const client = connect()
+      const topic = 'test'
+      const defaultOpts = { qos: 0 }
 
       client.once('connect', function () {
         client.subscribe(topic, {})
@@ -1815,7 +1832,7 @@ module.exports = function (server, config) {
 
       server.once('client', function (serverClient) {
         serverClient.once('subscribe', function (packet) {
-          var result = {
+          const result = {
             topic: topic,
             qos: defaultOpts.qos
           }
@@ -1832,8 +1849,8 @@ module.exports = function (server, config) {
     })
 
     it('should fire a callback on suback', function (done) {
-      var client = connect()
-      var topic = 'test'
+      const client = connect()
+      const topic = 'test'
 
       client.once('connect', function () {
         client.subscribe(topic, { qos: 2 }, function (err, granted) {
@@ -1841,7 +1858,7 @@ module.exports = function (server, config) {
             done(err)
           } else {
             assert.exists(granted, 'granted not given')
-            var expectedResult = {topic: 'test', qos: 2}
+            const expectedResult = { topic: 'test', qos: 2 }
             if (version === 5) {
               expectedResult.nl = false
               expectedResult.rap = false
@@ -1856,11 +1873,11 @@ module.exports = function (server, config) {
     })
 
     it('should fire a callback with error if disconnected (options provided)', function (done) {
-      var client = connect()
-      var topic = 'test'
+      const client = connect()
+      const topic = 'test'
       client.once('connect', function () {
         client.end(true, function () {
-          client.subscribe(topic, {qos: 2}, function (err, granted) {
+          client.subscribe(topic, { qos: 2 }, function (err, granted) {
             assert.notExists(granted, 'granted given')
             assert.exists(err, 'no error given')
             done()
@@ -1870,8 +1887,8 @@ module.exports = function (server, config) {
     })
 
     it('should fire a callback with error if disconnected (options not provided)', function (done) {
-      var client = connect()
-      var topic = 'test'
+      const client = connect()
+      const topic = 'test'
 
       client.once('connect', function () {
         client.end(true, function () {
@@ -1885,8 +1902,8 @@ module.exports = function (server, config) {
     })
 
     it('should subscribe with a chinese topic', function (done) {
-      var client = connect()
-      var topic = '中国'
+      const client = connect()
+      const topic = '中国'
 
       client.once('connect', function () {
         client.subscribe(topic)
@@ -1894,7 +1911,7 @@ module.exports = function (server, config) {
 
       server.once('client', function (serverClient) {
         serverClient.once('subscribe', function (packet) {
-          var result = {
+          const result = {
             topic: topic,
             qos: 0
           }
@@ -1912,8 +1929,8 @@ module.exports = function (server, config) {
 
   describe('receiving messages', function () {
     it('should fire the message event', function (done) {
-      var client = connect()
-      var testPacket = {
+      const client = connect()
+      const testPacket = {
         topic: 'test',
         payload: 'message',
         retain: true,
@@ -1938,8 +1955,8 @@ module.exports = function (server, config) {
     })
 
     it('should emit a packetreceive event', function (done) {
-      var client = connect()
-      var testPacket = {
+      const client = connect()
+      const testPacket = {
         topic: 'test',
         payload: 'message',
         retain: true,
@@ -1966,8 +1983,8 @@ module.exports = function (server, config) {
     })
 
     it('should support binary data', function (done) {
-      var client = connect({ encoding: 'binary' })
-      var testPacket = {
+      const client = connect({ encoding: 'binary' })
+      const testPacket = {
         topic: 'test',
         payload: 'message',
         retain: true,
@@ -1992,8 +2009,8 @@ module.exports = function (server, config) {
     })
 
     it('should emit a message event (qos=2)', function (done) {
-      var client = connect()
-      var testPacket = {
+      const client = connect()
+      const testPacket = {
         topic: 'test',
         payload: 'message',
         retain: true,
@@ -2020,8 +2037,8 @@ module.exports = function (server, config) {
     })
 
     it('should emit a message event (qos=2) - repeated publish', function (done) {
-      var client = connect()
-      var testPacket = {
+      const client = connect()
+      const testPacket = {
         topic: 'test',
         payload: 'message',
         retain: true,
@@ -2031,7 +2048,7 @@ module.exports = function (server, config) {
 
       server.testPublish = testPacket
 
-      var messageHandler = function (topic, message, packet) {
+      const messageHandler = function (topic, message, packet) {
         assert.strictEqual(topic, testPacket.topic)
         assert.strictEqual(message.toString(), testPacket.payload)
         assert.strictEqual(packet.messageId, testPacket.messageId)
@@ -2041,7 +2058,7 @@ module.exports = function (server, config) {
         client.end(true, done)
       }
 
-      var spiedMessageHandler = sinon.spy(messageHandler)
+      const spiedMessageHandler = sinon.spy(messageHandler)
 
       client.subscribe(testPacket.topic)
       client.on('message', spiedMessageHandler)
@@ -2056,8 +2073,8 @@ module.exports = function (server, config) {
     })
 
     it('should support a chinese topic', function (done) {
-      var client = connect({ encoding: 'binary' })
-      var testPacket = {
+      const client = connect({ encoding: 'binary' })
+      const testPacket = {
         topic: '国',
         payload: 'message',
         retain: true,
@@ -2085,12 +2102,12 @@ module.exports = function (server, config) {
 
   describe('qos handling', function () {
     it('should follow qos 0 semantics (trivial)', function (done) {
-      var client = connect()
-      var testTopic = 'test'
-      var testMessage = 'message'
+      const client = connect()
+      const testTopic = 'test'
+      const testMessage = 'message'
 
       client.once('connect', function () {
-        client.subscribe(testTopic, {qos: 0}, () => {
+        client.subscribe(testTopic, { qos: 0 }, () => {
           client.end(true, done)
         })
       })
@@ -2108,13 +2125,13 @@ module.exports = function (server, config) {
     })
 
     it('should follow qos 1 semantics', function (done) {
-      var client = connect()
-      var testTopic = 'test'
-      var testMessage = 'message'
-      var mid = 50
+      const client = connect()
+      const testTopic = 'test'
+      const testMessage = 'message'
+      const mid = 50
 
       client.once('connect', function () {
-        client.subscribe(testTopic, {qos: 1})
+        client.subscribe(testTopic, { qos: 1 })
       })
 
       server.once('client', function (serverClient) {
@@ -2135,16 +2152,16 @@ module.exports = function (server, config) {
     })
 
     it('should follow qos 2 semantics', function (done) {
-      var client = connect()
-      var testTopic = 'test'
-      var testMessage = 'message'
-      var mid = 253
-      var publishReceived = 0
-      var pubrecReceived = 0
-      var pubrelReceived = 0
+      const client = connect()
+      const testTopic = 'test'
+      const testMessage = 'message'
+      const mid = 253
+      let publishReceived = 0
+      let pubrecReceived = 0
+      let pubrelReceived = 0
 
       client.once('connect', function () {
-        client.subscribe(testTopic, {qos: 2})
+        client.subscribe(testTopic, { qos: 2 })
       })
 
       client.on('packetreceive', (packet) => {
@@ -2196,13 +2213,13 @@ module.exports = function (server, config) {
     })
 
     it('should should empty the incoming store after a qos 2 handshake is completed', function (done) {
-      var client = connect()
-      var testTopic = 'test'
-      var testMessage = 'message'
-      var mid = 253
+      const client = connect()
+      const testTopic = 'test'
+      const testMessage = 'message'
+      const mid = 253
 
       client.once('connect', function () {
-        client.subscribe(testTopic, {qos: 2})
+        client.subscribe(testTopic, { qos: 2 })
       })
 
       client.on('packetreceive', (packet) => {
@@ -2230,16 +2247,16 @@ module.exports = function (server, config) {
     })
 
     function testMultiplePubrel (shouldSendPubcompFail, done) {
-      var client = connect()
-      var testTopic = 'test'
-      var testMessage = 'message'
-      var mid = 253
-      var pubcompCount = 0
-      var pubrelCount = 0
-      var handleMessageCount = 0
-      var emitMessageCount = 0
-      var origSendPacket = client._sendPacket
-      var shouldSendFail
+      const client = connect()
+      const testTopic = 'test'
+      const testMessage = 'message'
+      const mid = 253
+      let pubcompCount = 0
+      let pubrelCount = 0
+      let handleMessageCount = 0
+      let emitMessageCount = 0
+      const origSendPacket = client._sendPacket
+      let shouldSendFail
 
       client.handleMessage = function (packet, callback) {
         handleMessageCount++
@@ -2258,14 +2275,16 @@ module.exports = function (server, config) {
 
         // send the mocked response
         switch (packet.cmd) {
-          case 'subscribe':
-            const suback = {cmd: 'suback', messageId: packet.messageId, granted: [2]}
+          case 'subscribe': {
+            const suback = { cmd: 'suback', messageId: packet.messageId, granted: [2] }
             client._handlePacket(suback, function (err) {
               assert.isNotOk(err)
             })
             break
+          }
           case 'pubrec':
           case 'pubcomp':
+          {
             // for both pubrec and pubcomp, reply with pubrel, simulating the server not receiving the pubcomp
             if (packet.cmd === 'pubcomp') {
               pubcompCount++
@@ -2281,7 +2300,7 @@ module.exports = function (server, config) {
             }
 
             // simulate the pubrel message, either in response to pubrec or to mock pubcomp failing to be received
-            const pubrel = {cmd: 'pubrel', messageId: mid}
+            const pubrel = { cmd: 'pubrel', messageId: mid }
             pubrelCount++
             client._handlePacket(pubrel, function (err) {
               if (shouldSendFail) {
@@ -2292,12 +2311,13 @@ module.exports = function (server, config) {
               }
             })
             break
+          }
         }
       }
 
       client.once('connect', function () {
-        client.subscribe(testTopic, {qos: 2})
-        const publish = {cmd: 'publish', topic: testTopic, payload: testMessage, qos: 2, messageId: mid}
+        client.subscribe(testTopic, { qos: 2 })
+        const publish = { cmd: 'publish', topic: testTopic, payload: testMessage, qos: 2, messageId: mid }
         client._handlePacket(publish, function (err) {
           assert.notExists(err)
         })
@@ -2315,7 +2335,7 @@ module.exports = function (server, config) {
 
   describe('auto reconnect', function () {
     it('should mark the client disconnecting if #end called', function (done) {
-      var client = connect()
+      const client = connect()
 
       client.end(true, err => {
         assert.isTrue(client.disconnecting)
@@ -2324,9 +2344,9 @@ module.exports = function (server, config) {
     })
 
     it('should reconnect after stream disconnect', function (done) {
-      var client = connect()
+      const client = connect()
 
-      var tryReconnect = true
+      let tryReconnect = true
 
       client.on('connect', function () {
         if (tryReconnect) {
@@ -2339,9 +2359,9 @@ module.exports = function (server, config) {
     })
 
     it('should emit \'reconnect\' when reconnecting', function (done) {
-      var client = connect()
-      var tryReconnect = true
-      var reconnectEvent = false
+      const client = connect()
+      let tryReconnect = true
+      let reconnectEvent = false
 
       client.on('reconnect', function () {
         reconnectEvent = true
@@ -2359,10 +2379,10 @@ module.exports = function (server, config) {
     })
 
     it('should emit \'offline\' after going offline', function (done) {
-      var client = connect()
+      const client = connect()
 
-      var tryReconnect = true
-      var offlineEvent = false
+      let tryReconnect = true
+      let offlineEvent = false
 
       client.on('offline', function () {
         offlineEvent = true
@@ -2380,7 +2400,7 @@ module.exports = function (server, config) {
     })
 
     it('should not reconnect if it was ended by the user', function (done) {
-      var client = connect()
+      const client = connect()
 
       client.on('connect', function () {
         client.end()
@@ -2389,7 +2409,7 @@ module.exports = function (server, config) {
     })
 
     it('should setup a reconnect timer on disconnect', function (done) {
-      var client = connect()
+      const client = connect()
 
       client.once('connect', function () {
         assert.notExists(client.reconnectTimer)
@@ -2402,14 +2422,15 @@ module.exports = function (server, config) {
       })
     })
 
-    var reconnectPeriodTests = [ {period: 200}, {period: 2000}, {period: 4000} ]
+    const reconnectPeriodTests = [{ period: 200 }, { period: 2000 }, { period: 4000 }]
     reconnectPeriodTests.forEach((test) => {
       it('should allow specification of a reconnect period (' + test.period + 'ms)', function (done) {
-        var end
-        var reconnectSlushTime = 200
-        var client = connect({reconnectPeriod: test.period})
-        var reconnect = false
-        var start = Date.now()
+        this.timeout(10000)
+        let end
+        const reconnectSlushTime = 200
+        const client = connect({ reconnectPeriod: test.period })
+        let reconnect = false
+        const start = Date.now()
 
         client.on('connect', function () {
           if (!reconnect) {
@@ -2418,7 +2439,7 @@ module.exports = function (server, config) {
           } else {
             end = Date.now()
             client.end(() => {
-              let reconnectPeriodDuringTest = end - start
+              const reconnectPeriodDuringTest = end - start
               if (reconnectPeriodDuringTest >= test.period - reconnectSlushTime && reconnectPeriodDuringTest <= test.period + reconnectSlushTime) {
                 // give the connection a 200 ms slush window
                 done()
@@ -2432,15 +2453,19 @@ module.exports = function (server, config) {
     })
 
     it('should always cleanup successfully on reconnection', function (done) {
-      var client = connect({host: 'this_hostname_should_not_exist', connectTimeout: 0, reconnectPeriod: 1})
+      const client = connect({ host: 'this_hostname_should_not_exist', connectTimeout: 0, reconnectPeriod: 1 })
       // bind client.end so that when it is called it is automatically passed in the done callback
-      setTimeout(client.end.bind(client, done), 50)
+      setTimeout(() => {
+        const boundEnd = client.end.bind(client, done)
+        boundEnd()
+      }, 50)
     })
 
     it('should resend in-flight QoS 1 publish messages from the client', function (done) {
-      var client = connect({reconnectPeriod: 200})
-      var serverPublished = false
-      var clientCalledBack = false
+      this.timeout(4000)
+      const client = connect({ reconnectPeriod: 200 })
+      let serverPublished = false
+      let clientCalledBack = false
 
       server.once('client', function (serverClient) {
         serverClient.on('connect', function () {
@@ -2470,9 +2495,9 @@ module.exports = function (server, config) {
     })
 
     it('should not resend in-flight publish messages if disconnecting', function (done) {
-      var client = connect({reconnectPeriod: 200})
-      var serverPublished = false
-      var clientCalledBack = false
+      const client = connect({ reconnectPeriod: 200 })
+      let serverPublished = false
+      let clientCalledBack = false
       server.once('client', function (serverClient) {
         serverClient.on('connect', function () {
           setImmediate(function () {
@@ -2496,9 +2521,9 @@ module.exports = function (server, config) {
     })
 
     it('should resend in-flight QoS 2 publish messages from the client', function (done) {
-      var client = connect({reconnectPeriod: 200})
-      var serverPublished = false
-      var clientCalledBack = false
+      const client = connect({ reconnectPeriod: 200 })
+      let serverPublished = false
+      let clientCalledBack = false
 
       server.once('client', function (serverClient) {
         // ignore errors
@@ -2530,8 +2555,8 @@ module.exports = function (server, config) {
     })
 
     it('should not resend in-flight QoS 1 removed publish messages from the client', function (done) {
-      var client = connect({reconnectPeriod: 200})
-      var clientCalledBack = false
+      const client = connect({ reconnectPeriod: 200 })
+      let clientCalledBack = false
 
       server.once('client', function (serverClient) {
         serverClient.on('connect', function () {
@@ -2565,8 +2590,8 @@ module.exports = function (server, config) {
     })
 
     it('should not resend in-flight QoS 2 removed publish messages from the client', function (done) {
-      var client = connect({reconnectPeriod: 200})
-      var clientCalledBack = false
+      const client = connect({ reconnectPeriod: 200 })
+      let clientCalledBack = false
 
       server.once('client', function (serverClient) {
         serverClient.on('connect', function () {
@@ -2597,9 +2622,9 @@ module.exports = function (server, config) {
     })
 
     it('should resubscribe when reconnecting', function (done) {
-      var client = connect({ reconnectPeriod: 100 })
-      var tryReconnect = true
-      var reconnectEvent = false
+      const client = connect({ reconnectPeriod: 100 })
+      let tryReconnect = true
+      let reconnectEvent = false
 
       client.on('reconnect', function () {
         reconnectEvent = true
@@ -2625,9 +2650,9 @@ module.exports = function (server, config) {
     })
 
     it('should not resubscribe when reconnecting if resubscribe is disabled', function (done) {
-      var client = connect({ reconnectPeriod: 100, resubscribe: false })
-      var tryReconnect = true
-      var reconnectEvent = false
+      const client = connect({ reconnectPeriod: 100, resubscribe: false })
+      let tryReconnect = true
+      let reconnectEvent = false
 
       client.on('reconnect', function () {
         reconnectEvent = true
@@ -2655,11 +2680,11 @@ module.exports = function (server, config) {
     })
 
     it('should not resubscribe when reconnecting if suback is error', function (done) {
-      var tryReconnect = true
-      var reconnectEvent = false
-      var server2 = serverBuilder(config.protocol, function (serverClient) {
+      let tryReconnect = true
+      let reconnectEvent = false
+      const server2 = serverBuilder(config.protocol, function (serverClient) {
         serverClient.on('connect', function (packet) {
-          var connack = version === 5 ? { reasonCode: 0 } : { returnCode: 0 }
+          const connack = version === 5 ? { reasonCode: 0 } : { returnCode: 0 }
           serverClient.connack(connack)
         })
         serverClient.on('subscribe', function (packet) {
@@ -2674,7 +2699,7 @@ module.exports = function (server, config) {
       })
 
       server2.listen(ports.PORTAND49, function () {
-        var client = connect({
+        const client = connect({
           port: ports.PORTAND49,
           host: 'localhost',
           reconnectPeriod: 100
@@ -2707,13 +2732,13 @@ module.exports = function (server, config) {
     })
 
     it('should preserved incomingStore after disconnecting if clean is false', function (done) {
-      var reconnect = false
-      var client = {}
-      var incomingStore = new mqtt.Store({ clean: false })
-      var outgoingStore = new mqtt.Store({ clean: false })
-      var server2 = serverBuilder(config.protocol, function (serverClient) {
+      let reconnect = false
+      let client = {}
+      const incomingStore = new mqtt.Store({ clean: false })
+      const outgoingStore = new mqtt.Store({ clean: false })
+      const server2 = serverBuilder(config.protocol, function (serverClient) {
         serverClient.on('connect', function (packet) {
-          var connack = version === 5 ? { reasonCode: 0 } : { returnCode: 0 }
+          const connack = version === 5 ? { reasonCode: 0 } : { returnCode: 0 }
           serverClient.connack(connack)
           if (reconnect) {
             serverClient.pubrel({ messageId: 1 })
@@ -2757,7 +2782,7 @@ module.exports = function (server, config) {
 
         client.on('connect', function () {
           if (!reconnect) {
-            client.subscribe('test', {qos: 2}, function () {
+            client.subscribe('test', { qos: 2 }, function () {
             })
             reconnect = true
           }
@@ -2770,11 +2795,11 @@ module.exports = function (server, config) {
     })
 
     it('should clear outgoing if close from server', function (done) {
-      var reconnect = false
-      var client = {}
-      var server2 = serverBuilder(config.protocol, function (serverClient) {
+      let reconnect = false
+      let client = {}
+      const server2 = serverBuilder(config.protocol, function (serverClient) {
         serverClient.on('connect', function (packet) {
-          var connack = version === 5 ? { reasonCode: 0 } : { returnCode: 0 }
+          const connack = version === 5 ? { reasonCode: 0 } : { returnCode: 0 }
           serverClient.connack(connack)
         })
         serverClient.on('subscribe', function (packet) {
@@ -2802,7 +2827,7 @@ module.exports = function (server, config) {
         })
 
         client.on('connect', function () {
-          client.subscribe('test', {qos: 2}, function (e) {
+          client.subscribe('test', { qos: 2 }, function (e) {
             if (!e) {
               client.end()
             }
@@ -2823,13 +2848,13 @@ module.exports = function (server, config) {
     })
 
     it('should resend in-flight QoS 1 publish messages from the client if clean is false', function (done) {
-      var reconnect = false
-      var client = {}
-      var incomingStore = new mqtt.Store({ clean: false })
-      var outgoingStore = new mqtt.Store({ clean: false })
-      var server2 = serverBuilder(config.protocol, function (serverClient) {
+      let reconnect = false
+      let client = {}
+      const incomingStore = new mqtt.Store({ clean: false })
+      const outgoingStore = new mqtt.Store({ clean: false })
+      const server2 = serverBuilder(config.protocol, function (serverClient) {
         serverClient.on('connect', function (packet) {
-          var connack = version === 5 ? { reasonCode: 0 } : { returnCode: 0 }
+          const connack = version === 5 ? { reasonCode: 0 } : { returnCode: 0 }
           serverClient.connack(connack)
         })
         serverClient.on('publish', function (packet) {
@@ -2861,7 +2886,7 @@ module.exports = function (server, config) {
 
         client.on('connect', function () {
           if (!reconnect) {
-            client.publish('topic', 'payload', {qos: 1})
+            client.publish('topic', 'payload', { qos: 1 })
           }
         })
         client.on('error', function () {})
@@ -2869,13 +2894,13 @@ module.exports = function (server, config) {
     })
 
     it('should resend in-flight QoS 2 publish messages from the client if clean is false', function (done) {
-      var reconnect = false
-      var client = {}
-      var incomingStore = new mqtt.Store({ clean: false })
-      var outgoingStore = new mqtt.Store({ clean: false })
-      var server2 = serverBuilder(config.protocol, function (serverClient) {
+      let reconnect = false
+      let client = {}
+      const incomingStore = new mqtt.Store({ clean: false })
+      const outgoingStore = new mqtt.Store({ clean: false })
+      const server2 = serverBuilder(config.protocol, function (serverClient) {
         serverClient.on('connect', function (packet) {
-          var connack = version === 5 ? { reasonCode: 0 } : { returnCode: 0 }
+          const connack = version === 5 ? { reasonCode: 0 } : { returnCode: 0 }
           serverClient.connack(connack)
         })
         serverClient.on('publish', function (packet) {
@@ -2907,7 +2932,7 @@ module.exports = function (server, config) {
 
         client.on('connect', function () {
           if (!reconnect) {
-            client.publish('topic', 'payload', {qos: 2})
+            client.publish('topic', 'payload', { qos: 2 })
           }
         })
         client.on('error', function () {})
@@ -2915,18 +2940,18 @@ module.exports = function (server, config) {
     })
 
     it('should resend in-flight QoS 2 pubrel messages from the client if clean is false', function (done) {
-      var reconnect = false
-      var client = {}
-      var incomingStore = new mqtt.Store({ clean: false })
-      var outgoingStore = new mqtt.Store({ clean: false })
-      var server2 = serverBuilder(config.protocol, function (serverClient) {
+      let reconnect = false
+      let client = {}
+      const incomingStore = new mqtt.Store({ clean: false })
+      const outgoingStore = new mqtt.Store({ clean: false })
+      const server2 = serverBuilder(config.protocol, function (serverClient) {
         serverClient.on('connect', function (packet) {
-          var connack = version === 5 ? { reasonCode: 0 } : { returnCode: 0 }
+          const connack = version === 5 ? { reasonCode: 0 } : { returnCode: 0 }
           serverClient.connack(connack)
         })
         serverClient.on('publish', function (packet) {
           if (!reconnect) {
-            serverClient.pubrec({messageId: packet.messageId})
+            serverClient.pubrec({ messageId: packet.messageId })
           }
         })
         serverClient.on('pubrel', function () {
@@ -2958,7 +2983,7 @@ module.exports = function (server, config) {
 
         client.on('connect', function () {
           if (!reconnect) {
-            client.publish('topic', 'payload', {qos: 2})
+            client.publish('topic', 'payload', { qos: 2 })
           }
         })
         client.on('error', function () {})
@@ -2966,23 +2991,23 @@ module.exports = function (server, config) {
     })
 
     it('should resend in-flight publish messages by published order', function (done) {
-      var publishCount = 0
-      var reconnect = false
-      var disconnectOnce = true
-      var client = {}
-      var incomingStore = new mqtt.Store({ clean: false })
-      var outgoingStore = new mqtt.Store({ clean: false })
-      var server2 = serverBuilder(config.protocol, function (serverClient) {
+      let publishCount = 0
+      let reconnect = false
+      let disconnectOnce = true
+      let client = {}
+      const incomingStore = new mqtt.Store({ clean: false })
+      const outgoingStore = new mqtt.Store({ clean: false })
+      const server2 = serverBuilder(config.protocol, function (serverClient) {
         // errors are not interesting for this test
         // but they might happen on some platforms
         serverClient.on('error', function () {})
 
         serverClient.on('connect', function (packet) {
-          var connack = version === 5 ? { reasonCode: 0 } : { returnCode: 0 }
+          const connack = version === 5 ? { reasonCode: 0 } : { returnCode: 0 }
           serverClient.connack(connack)
         })
         serverClient.on('publish', function (packet) {
-          serverClient.puback({messageId: packet.messageId})
+          serverClient.puback({ messageId: packet.messageId })
           if (reconnect) {
             switch (publishCount++) {
               case 0:
@@ -3027,9 +3052,9 @@ module.exports = function (server, config) {
 
         client.on('connect', function () {
           if (!reconnect) {
-            client.publish('topic', 'payload1', {qos: 1})
-            client.publish('topic', 'payload2', {qos: 1})
-            client.publish('topic', 'payload3', {qos: 1})
+            client.publish('topic', 'payload1', { qos: 1 })
+            client.publish('topic', 'payload2', { qos: 1 })
+            client.publish('topic', 'payload3', { qos: 1 })
           }
         })
         client.on('error', function () {})
@@ -3037,9 +3062,9 @@ module.exports = function (server, config) {
     })
 
     it('should be able to pub/sub if reconnect() is called at close handler', function (done) {
-      var client = connect({ reconnectPeriod: 0 })
-      var tryReconnect = true
-      var reconnectEvent = false
+      const client = connect({ reconnectPeriod: 0 })
+      let tryReconnect = true
+      let reconnectEvent = false
 
       client.on('close', function () {
         if (tryReconnect) {
@@ -3067,9 +3092,9 @@ module.exports = function (server, config) {
     })
 
     it('should be able to pub/sub if reconnect() is called at out of close handler', function (done) {
-      var client = connect({ reconnectPeriod: 0 })
-      var tryReconnect = true
-      var reconnectEvent = false
+      const client = connect({ reconnectPeriod: 0 })
+      let tryReconnect = true
+      let reconnectEvent = false
 
       client.on('close', function () {
         if (tryReconnect) {
@@ -3099,8 +3124,8 @@ module.exports = function (server, config) {
     })
 
     context('with alternate server client', function () {
-      var cachedClientListeners
-      var connack = version === 5 ? { reasonCode: 0 } : { returnCode: 0 }
+      let cachedClientListeners
+      const connack = version === 5 ? { reasonCode: 0 } : { returnCode: 0 }
 
       beforeEach(function () {
         cachedClientListeners = server.listeners('client')
@@ -3115,9 +3140,9 @@ module.exports = function (server, config) {
       })
 
       it('should resubscribe even if disconnect is before suback', function (done) {
-        var client = connect(Object.assign({ reconnectPeriod: 100 }, config))
-        var subscribeCount = 0
-        var connectCount = 0
+        const client = connect(Object.assign({ reconnectPeriod: 100 }, config))
+        let subscribeCount = 0
+        let connectCount = 0
 
         server.on('client', function (serverClient) {
           serverClient.on('connect', function () {
@@ -3146,8 +3171,8 @@ module.exports = function (server, config) {
       })
 
       it('should resubscribe exactly once', function (done) {
-        var client = connect(Object.assign({ reconnectPeriod: 100 }, config))
-        var subscribeCount = 0
+        const client = connect(Object.assign({ reconnectPeriod: 100 }, config))
+        let subscribeCount = 0
 
         server.on('client', function (serverClient) {
           serverClient.on('connect', function () {
diff --git a/test/abstract_store.js b/test/abstract_store.js
index 02b3ec849..bae4bb033 100644
--- a/test/abstract_store.js
+++ b/test/abstract_store.js
@@ -3,8 +3,9 @@
 require('should')
 
 module.exports = function abstractStoreTest (build) {
-  var store
+  let store
 
+  // eslint-disable-next-line
   beforeEach(function (done) {
     build(function (err, _store) {
       store = _store
@@ -17,7 +18,7 @@ module.exports = function abstractStoreTest (build) {
   })
 
   it('should put and stream in-flight packets', function (done) {
-    var packet = {
+    const packet = {
       topic: 'hello',
       payload: 'world',
       qos: 1,
@@ -35,7 +36,7 @@ module.exports = function abstractStoreTest (build) {
   })
 
   it('should support destroying the stream', function (done) {
-    var packet = {
+    const packet = {
       topic: 'hello',
       payload: 'world',
       qos: 1,
@@ -43,14 +44,14 @@ module.exports = function abstractStoreTest (build) {
     }
 
     store.put(packet, function () {
-      var stream = store.createStream()
+      const stream = store.createStream()
       stream.on('close', done)
       stream.destroy()
     })
   })
 
   it('should add and del in-flight packets', function (done) {
-    var packet = {
+    const packet = {
       topic: 'hello',
       payload: 'world',
       qos: 1,
@@ -70,14 +71,14 @@ module.exports = function abstractStoreTest (build) {
   })
 
   it('should replace a packet when doing put with the same messageId', function (done) {
-    var packet1 = {
+    const packet1 = {
       cmd: 'publish', // added
       topic: 'hello',
       payload: 'world',
       qos: 2,
       messageId: 42
     }
-    var packet2 = {
+    const packet2 = {
       cmd: 'pubrel', // added
       qos: 2,
       messageId: 42
@@ -96,7 +97,7 @@ module.exports = function abstractStoreTest (build) {
   })
 
   it('should return the original packet on del', function (done) {
-    var packet = {
+    const packet = {
       topic: 'hello',
       payload: 'world',
       qos: 1,
@@ -115,7 +116,7 @@ module.exports = function abstractStoreTest (build) {
   })
 
   it('should get a packet with the same messageId', function (done) {
-    var packet = {
+    const packet = {
       topic: 'hello',
       payload: 'world',
       qos: 1,
diff --git a/test/browser/server.js b/test/browser/server.js
index 75a9a8994..b1dcf2969 100644
--- a/test/browser/server.js
+++ b/test/browser/server.js
@@ -1,13 +1,12 @@
 'use strict'
 
-var handleClient
-var WS = require('ws')
-var WebSocketServer = WS.Server
-var Connection = require('mqtt-connection')
-var http = require('http')
+const WS = require('ws')
+const WebSocketServer = WS.Server
+const Connection = require('mqtt-connection')
+const http = require('http')
 
-handleClient = function (client) {
-  var self = this
+const handleClient = function (client) {
+  const self = this
 
   if (!self.clients) {
     self.clients = {}
@@ -15,16 +14,16 @@ handleClient = function (client) {
 
   client.on('connect', function (packet) {
     if (packet.clientId === 'invalid') {
-      client.connack({returnCode: 2})
+      client.connack({ returnCode: 2 })
     } else {
-      client.connack({returnCode: 0})
+      client.connack({ returnCode: 0 })
     }
     self.clients[packet.clientId] = client
     client.subscriptions = []
   })
 
   client.on('publish', function (packet) {
-    var i, k, c, s, publish
+    let k, c, s, publish
     switch (packet.qos) {
       case 0:
         break
@@ -40,7 +39,7 @@ handleClient = function (client) {
       c = self.clients[k]
       publish = false
 
-      for (i = 0; i < c.subscriptions.length; i++) {
+      for (let i = 0; i < c.subscriptions.length; i++) {
         s = c.subscriptions[i]
 
         if (s.test(packet.topic)) {
@@ -50,7 +49,7 @@ handleClient = function (client) {
 
       if (publish) {
         try {
-          c.publish({topic: packet.topic, payload: packet.payload})
+          c.publish({ topic: packet.topic, payload: packet.payload })
         } catch (error) {
           delete self.clients[k]
         }
@@ -71,12 +70,10 @@ handleClient = function (client) {
   })
 
   client.on('subscribe', function (packet) {
-    var qos
-    var topic
-    var reg
-    var granted = []
+    let qos, topic, reg
+    const granted = []
 
-    for (var i = 0; i < packet.subscriptions.length; i++) {
+    for (let i = 0; i < packet.subscriptions.length; i++) {
       qos = packet.subscriptions[i].qos
       topic = packet.subscriptions[i].topic
       reg = new RegExp(topic.replace('+', '[^/]+').replace('#', '.+') + '$')
@@ -85,7 +82,7 @@ handleClient = function (client) {
       client.subscriptions.push(reg)
     }
 
-    client.suback({messageId: packet.messageId, granted: granted})
+    client.suback({ messageId: packet.messageId, granted: granted })
   })
 
   client.on('unsubscribe', function (packet) {
@@ -98,19 +95,17 @@ handleClient = function (client) {
 }
 
 function start (startPort, done) {
-  var server = http.createServer()
-  var wss = new WebSocketServer({server: server})
+  const server = http.createServer()
+  const wss = new WebSocketServer({ server: server })
 
   wss.on('connection', function (ws) {
-    var stream, connection
-
     if (!(ws.protocol === 'mqtt' ||
           ws.protocol === 'mqttv3.1')) {
       return ws.close()
     }
 
-    stream = WS.createWebSocketStream(ws)
-    connection = new Connection(stream)
+    const stream = WS.createWebSocketStream(ws)
+    const connection = new Connection(stream)
     handleClient.call(server, connection)
   })
   server.listen(startPort, done)
diff --git a/test/browser/test.js b/test/browser/test.js
index 8e9cd42e3..e1dcc39cc 100644
--- a/test/browser/test.js
+++ b/test/browser/test.js
@@ -1,17 +1,19 @@
 'use strict'
 
-var mqtt = require('../../lib/connect')
-var xtend = require('xtend')
-var _URL = require('url')
-var parsed = _URL.parse(document.URL)
-var isHttps = parsed.protocol === 'https:'
-var port = parsed.port || (isHttps ? 443 : 80)
-var host = parsed.hostname
-var protocol = isHttps ? 'wss' : 'ws'
+const mqtt = require('../../lib/connect')
+const xtend = require('xtend')
+const _URL = require('url')
+// eslint-disable-next-line
+const parsed = _URL.parse(document.URL)
+const isHttps = parsed.protocol === 'https:'
+const port = parsed.port || (isHttps ? 443 : 80)
+const host = parsed.hostname
+const protocol = isHttps ? 'wss' : 'ws'
 
 function clientTests (buildClient) {
-  var client
+  let client
 
+  // eslint-disable-next-line
   beforeEach(function () {
     client = buildClient()
     client.on('offline', function () {
@@ -50,7 +52,7 @@ function suiteFactory (configName, opts) {
     return xtend(base || {}, opts)
   }
 
-  var suiteName = 'MqttClient(' + configName + '=' + JSON.stringify(opts) + ')'
+  const suiteName = 'MqttClient(' + configName + '=' + JSON.stringify(opts) + ')'
   describe(suiteName, function () {
     this.timeout(10000)
 
@@ -88,5 +90,5 @@ function suiteFactory (configName, opts) {
   })
 }
 
-suiteFactory('v3', {protocolId: 'MQIsdp', protocolVersion: 3})
+suiteFactory('v3', { protocolId: 'MQIsdp', protocolVersion: 3 })
 suiteFactory('default', {})
diff --git a/test/client.js b/test/client.js
index 4ea052ab8..bac6434da 100644
--- a/test/client.js
+++ b/test/client.js
@@ -1,25 +1,25 @@
 'use strict'
 
-var mqtt = require('..')
-var assert = require('chai').assert
+const mqtt = require('..')
+const assert = require('chai').assert
 const { fork } = require('child_process')
-var path = require('path')
-var abstractClientTests = require('./abstract_client')
-var net = require('net')
-var eos = require('end-of-stream')
-var mqttPacket = require('mqtt-packet')
-var Duplex = require('readable-stream').Duplex
-var Connection = require('mqtt-connection')
-var MqttServer = require('./server').MqttServer
-var util = require('util')
-var ports = require('./helpers/port_list')
-var serverBuilder = require('./server_helpers_for_client_tests').serverBuilder
-var debug = require('debug')('TEST:client')
+const path = require('path')
+const abstractClientTests = require('./abstract_client')
+const net = require('net')
+const eos = require('end-of-stream')
+const mqttPacket = require('mqtt-packet')
+const Duplex = require('readable-stream').Duplex
+const Connection = require('mqtt-connection')
+const MqttServer = require('./server').MqttServer
+const util = require('util')
+const ports = require('./helpers/port_list')
+const serverBuilder = require('./server_helpers_for_client_tests').serverBuilder
+const debug = require('debug')('TEST:client')
 
 describe('MqttClient', function () {
-  var client
-  var server = serverBuilder('mqtt')
-  var config = {protocol: 'mqtt', port: ports.PORT}
+  let client
+  const server = serverBuilder('mqtt')
+  const config = { protocol: 'mqtt', port: ports.PORT }
   server.listen(ports.PORT)
 
   after(function () {
@@ -48,16 +48,16 @@ describe('MqttClient', function () {
   describe('message ids', function () {
     it('should increment the message id', function () {
       client = mqtt.connect(config)
-      var currentId = client._nextId()
+      const currentId = client._nextId()
 
       assert.equal(client._nextId(), currentId + 1)
       client.end()
     })
 
     it('should not throw an error if packet\'s messageId is not found when receiving a pubrel packet', function (done) {
-      var server2 = new MqttServer(function (serverClient) {
+      const server2 = new MqttServer(function (serverClient) {
         serverClient.on('connect', function (packet) {
-          serverClient.connack({returnCode: 0})
+          serverClient.connack({ returnCode: 0 })
           serverClient.pubrel({ messageId: Math.floor(Math.random() * 9000) + 1000 })
         })
       })
@@ -79,10 +79,10 @@ describe('MqttClient', function () {
     })
 
     it('should not go overflow if the TCP frame contains a lot of PUBLISH packets', function (done) {
-      var parser = mqttPacket.parser()
-      var count = 0
-      var max = 1000
-      var duplex = new Duplex({
+      const parser = mqttPacket.parser()
+      const max = 1000
+      let count = 0
+      const duplex = new Duplex({
         read: function (n) {},
         write: function (chunk, enc, cb) {
           parser.parse(chunk)
@@ -100,7 +100,7 @@ describe('MqttClient', function () {
       })
 
       parser.on('packet', function (packet) {
-        var packets = []
+        const packets = []
 
         if (packet.cmd === 'connect') {
           duplex.push(mqttPacket.generate({
@@ -109,7 +109,7 @@ describe('MqttClient', function () {
             returnCode: 0
           }))
 
-          for (var i = 0; i < max; i++) {
+          for (let i = 0; i < max; i++) {
             packets.push(mqttPacket.generate({
               cmd: 'publish',
               topic: Buffer.from('hello'),
@@ -130,14 +130,14 @@ describe('MqttClient', function () {
   describe('flushing', function () {
     it('should attempt to complete pending unsub and send on ping timeout', function (done) {
       this.timeout(10000)
-      var server3 = new MqttServer(function (client) {
+      const server3 = new MqttServer(function (client) {
         client.on('connect', function (packet) {
-          client.connack({returnCode: 0})
+          client.connack({ returnCode: 0 })
         })
       }).listen(ports.PORTAND72)
 
-      var pubCallbackCalled = false
-      var unsubscribeCallbackCalled = false
+      let pubCallbackCalled = false
+      let unsubscribeCallbackCalled = false
       client = mqtt.connect({
         port: ports.PORTAND72,
         host: 'localhost',
@@ -146,7 +146,7 @@ describe('MqttClient', function () {
         reconnectPeriod: 0
       })
       client.once('connect', () => {
-        client.publish('fakeTopic', 'fakeMessage', {qos: 1}, (err, result) => {
+        client.publish('fakeTopic', 'fakeMessage', { qos: 1 }, (err, result) => {
           assert.exists(err)
           pubCallbackCalled = true
         })
@@ -169,7 +169,7 @@ describe('MqttClient', function () {
     it('should attempt to reconnect once server is down', function (done) {
       this.timeout(30000)
 
-      var innerServer = fork(path.join(__dirname, 'helpers', 'server_process.js'), { execArgv: ['--inspect'] })
+      const innerServer = fork(path.join(__dirname, 'helpers', 'server_process.js'), { execArgv: ['--inspect'] })
       innerServer.on('close', (code) => {
         if (code) {
           done(util.format('child process closed with code %d', code))
@@ -195,7 +195,7 @@ describe('MqttClient', function () {
     it('should reconnect if a connack is not received in an interval', function (done) {
       this.timeout(2000)
 
-      var server2 = net.createServer().listen(ports.PORTAND43)
+      const server2 = net.createServer().listen(ports.PORTAND43)
 
       server2.on('connection', function (c) {
         eos(c, function () {
@@ -213,7 +213,7 @@ describe('MqttClient', function () {
         })
 
         server.once('client', function () {
-          client.end(true, (err) => {
+          client.end(false, (err) => {
             done(err)
           })
         })
@@ -227,17 +227,17 @@ describe('MqttClient', function () {
     it('should not be cleared by the connack timer', function (done) {
       this.timeout(4000)
 
-      var server2 = net.createServer().listen(ports.PORTAND44)
+      const server2 = net.createServer().listen(ports.PORTAND44)
 
       server2.on('connection', function (c) {
         c.destroy()
       })
 
       server2.once('listening', function () {
-        var reconnects = 0
-        var connectTimeout = 1000
-        var reconnectPeriod = 100
-        var expectedReconnects = Math.floor(connectTimeout / reconnectPeriod)
+        const connectTimeout = 1000
+        const reconnectPeriod = 100
+        const expectedReconnects = Math.floor(connectTimeout / reconnectPeriod)
+        let reconnects = 0
         client = mqtt.connect({
           port: ports.PORTAND44,
           host: 'localhost',
@@ -257,7 +257,7 @@ describe('MqttClient', function () {
     it('should not keep requeueing the first message when offline', function (done) {
       this.timeout(2500)
 
-      var server2 = serverBuilder('mqtt').listen(ports.PORTAND45)
+      const server2 = serverBuilder('mqtt').listen(ports.PORTAND45)
       client = mqtt.connect({
         port: ports.PORTAND45,
         host: 'localhost',
@@ -289,9 +289,9 @@ describe('MqttClient', function () {
     it('should not send the same subscribe multiple times on a flaky connection', function (done) {
       this.timeout(3500)
 
-      var KILL_COUNT = 4
-      var killedConnections = 0
-      var subIds = {}
+      const KILL_COUNT = 4
+      const subIds = {}
+      let killedConnections = 0
       client = mqtt.connect({
         port: ports.PORTAND46,
         host: 'localhost',
@@ -299,16 +299,16 @@ describe('MqttClient', function () {
         reconnectPeriod: 300
       })
 
-      var server2 = new MqttServer(function (serverClient) {
+      const server2 = new MqttServer(function (serverClient) {
         serverClient.on('error', function () {})
         debug('setting serverClient connect callback')
         serverClient.on('connect', function (packet) {
           if (packet.clientId === 'invalid') {
             debug('connack with returnCode 2')
-            serverClient.connack({returnCode: 2})
+            serverClient.connack({ returnCode: 2 })
           } else {
             debug('connack with returnCode 0')
-            serverClient.connack({returnCode: 0})
+            serverClient.connack({ returnCode: 0 })
           }
         })
       }).listen(ports.PORTAND46)
@@ -353,12 +353,12 @@ describe('MqttClient', function () {
 
     it('should not fill the queue of subscribes if it cannot connect', function (done) {
       this.timeout(2500)
-      var server2 = net.createServer(function (stream) {
-        var serverClient = new Connection(stream)
+      const server2 = net.createServer(function (stream) {
+        const serverClient = new Connection(stream)
 
         serverClient.on('error', function (e) { /* do nothing */ })
         serverClient.on('connect', function (packet) {
-          serverClient.connack({returnCode: 0})
+          serverClient.connack({ returnCode: 0 })
           serverClient.destroy()
         })
       })
@@ -385,9 +385,9 @@ describe('MqttClient', function () {
     it('should not send the same publish multiple times on a flaky connection', function (done) {
       this.timeout(3500)
 
-      var KILL_COUNT = 4
-      var killedConnections = 0
-      var pubIds = {}
+      const KILL_COUNT = 4
+      let killedConnections = 0
+      const pubIds = {}
       client = mqtt.connect({
         port: ports.PORTAND47,
         host: 'localhost',
@@ -395,14 +395,14 @@ describe('MqttClient', function () {
         reconnectPeriod: 300
       })
 
-      var server2 = net.createServer(function (stream) {
-        var serverClient = new Connection(stream)
+      const server2 = net.createServer(function (stream) {
+        const serverClient = new Connection(stream)
         serverClient.on('error', function () {})
         serverClient.on('connect', function (packet) {
           if (packet.clientId === 'invalid') {
-            serverClient.connack({returnCode: 2})
+            serverClient.connack({ returnCode: 2 })
           } else {
-            serverClient.connack({returnCode: 0})
+            serverClient.connack({ returnCode: 0 })
           }
         })
 
@@ -449,7 +449,7 @@ describe('MqttClient', function () {
   it('check emit error on checkDisconnection w/o callback', function (done) {
     this.timeout(15000)
 
-    var server118 = new MqttServer(function (client) {
+    const server118 = new MqttServer(function (client) {
       client.on('connect', function (packet) {
         client.connack({
           reasonCode: 0
@@ -463,7 +463,7 @@ describe('MqttClient', function () {
       })
     }).listen(ports.PORTAND118)
 
-    var opts = {
+    const opts = {
       host: 'localhost',
       port: ports.PORTAND118,
       protocolVersion: 5
diff --git a/test/client_mqtt5.js b/test/client_mqtt5.js
index fd2bb9979..9e5301ed6 100644
--- a/test/client_mqtt5.js
+++ b/test/client_mqtt5.js
@@ -1,30 +1,30 @@
 'use strict'
 
-var mqtt = require('..')
-var abstractClientTests = require('./abstract_client')
-var MqttServer = require('./server').MqttServer
-var assert = require('chai').assert
-var serverBuilder = require('./server_helpers_for_client_tests').serverBuilder
-var ports = require('./helpers/port_list')
+const mqtt = require('..')
+const abstractClientTests = require('./abstract_client')
+const MqttServer = require('./server').MqttServer
+const assert = require('chai').assert
+const serverBuilder = require('./server_helpers_for_client_tests').serverBuilder
+const ports = require('./helpers/port_list')
 
 describe('MQTT 5.0', function () {
-  var server = serverBuilder('mqtt').listen(ports.PORTAND115)
-  var config = { protocol: 'mqtt', port: ports.PORTAND115, protocolVersion: 5, properties: { maximumPacketSize: 200 } }
+  const server = serverBuilder('mqtt').listen(ports.PORTAND115)
+  const config = { protocol: 'mqtt', port: ports.PORTAND115, protocolVersion: 5, properties: { maximumPacketSize: 200 } }
 
   abstractClientTests(server, config)
 
   it('topic should be complemented on receive', function (done) {
     this.timeout(15000)
 
-    var opts = {
+    const opts = {
       host: 'localhost',
       port: ports.PORTAND103,
       protocolVersion: 5,
       topicAliasMaximum: 3
     }
-    var client = mqtt.connect(opts)
-    var publishCount = 0
-    var server103 = new MqttServer(function (serverClient) {
+    const client = mqtt.connect(opts)
+    let publishCount = 0
+    const server103 = new MqttServer(function (serverClient) {
       serverClient.on('connect', function (packet) {
         assert.strictEqual(packet.properties.topicAliasMaximum, 3)
         serverClient.connack({
@@ -96,16 +96,16 @@ describe('MQTT 5.0', function () {
   it('registered topic alias should automatically used if autoUseTopicAlias is true', function (done) {
     this.timeout(15000)
 
-    var opts = {
+    const opts = {
       host: 'localhost',
       port: ports.PORTAND103,
       protocolVersion: 5,
       autoUseTopicAlias: true
     }
-    var client = mqtt.connect(opts)
+    const client = mqtt.connect(opts)
 
-    var publishCount = 0
-    var server103 = new MqttServer(function (serverClient) {
+    let publishCount = 0
+    const server103 = new MqttServer(function (serverClient) {
       serverClient.on('connect', function (packet) {
         serverClient.connack({
           reasonCode: 0,
@@ -147,16 +147,16 @@ describe('MQTT 5.0', function () {
   it('topicAlias is automatically used if autoAssignTopicAlias is true', function (done) {
     this.timeout(15000)
 
-    var opts = {
+    const opts = {
       host: 'localhost',
       port: ports.PORTAND103,
       protocolVersion: 5,
       autoAssignTopicAlias: true
     }
-    var client = mqtt.connect(opts)
+    const client = mqtt.connect(opts)
 
-    var publishCount = 0
-    var server103 = new MqttServer(function (serverClient) {
+    let publishCount = 0
+    const server103 = new MqttServer(function (serverClient) {
       serverClient.on('connect', function (packet) {
         serverClient.connack({
           reasonCode: 0,
@@ -215,9 +215,9 @@ describe('MQTT 5.0', function () {
   it('topicAlias should be removed and topic restored on resend', function (done) {
     this.timeout(15000)
 
-    var incomingStore = new mqtt.Store({ clean: false })
-    var outgoingStore = new mqtt.Store({ clean: false })
-    var opts = {
+    const incomingStore = new mqtt.Store({ clean: false })
+    const outgoingStore = new mqtt.Store({ clean: false })
+    const opts = {
       host: 'localhost',
       port: ports.PORTAND103,
       protocolVersion: 5,
@@ -227,11 +227,11 @@ describe('MQTT 5.0', function () {
       clean: false,
       reconnectPeriod: 100
     }
-    var client = mqtt.connect(opts)
+    const client = mqtt.connect(opts)
 
-    var connectCount = 0
-    var publishCount = 0
-    var server103 = new MqttServer(function (serverClient) {
+    let connectCount = 0
+    let publishCount = 0
+    const server103 = new MqttServer(function (serverClient) {
       serverClient.on('connect', function (packet) {
         switch (connectCount++) {
           case 0:
@@ -267,26 +267,28 @@ describe('MQTT 5.0', function () {
               serverClient.stream.destroy()
             })
             break
-          case 2:
+          case 2: {
             assert.strictEqual(packet.topic, 'test1')
-            var alias1
+            let alias1
             if (packet.properties) {
               alias1 = packet.properties.topicAlias
             }
             assert.strictEqual(alias1, undefined)
-            serverClient.puback({messageId: packet.messageId})
+            serverClient.puback({ messageId: packet.messageId })
             break
-          case 3:
+          }
+          case 3: {
             assert.strictEqual(packet.topic, 'test1')
-            var alias2
+            let alias2
             if (packet.properties) {
               alias2 = packet.properties.topicAlias
             }
             assert.strictEqual(alias2, undefined)
-            serverClient.puback({messageId: packet.messageId})
+            serverClient.puback({ messageId: packet.messageId })
             server103.close()
             client.end(true, done)
             break
+          }
         }
       })
     }).listen(ports.PORTAND103)
@@ -302,9 +304,9 @@ describe('MQTT 5.0', function () {
   it('topicAlias should be removed and topic restored on offline publish', function (done) {
     this.timeout(15000)
 
-    var incomingStore = new mqtt.Store({ clean: false })
-    var outgoingStore = new mqtt.Store({ clean: false })
-    var opts = {
+    const incomingStore = new mqtt.Store({ clean: false })
+    const outgoingStore = new mqtt.Store({ clean: false })
+    const opts = {
       host: 'localhost',
       port: ports.PORTAND103,
       protocolVersion: 5,
@@ -314,11 +316,11 @@ describe('MQTT 5.0', function () {
       clean: false,
       reconnectPeriod: 100
     }
-    var client = mqtt.connect(opts)
+    const client = mqtt.connect(opts)
 
-    var connectCount = 0
-    var publishCount = 0
-    var server103 = new MqttServer(function (serverClient) {
+    let connectCount = 0
+    let publishCount = 0
+    const server103 = new MqttServer(function (serverClient) {
       serverClient.on('connect', function (packet) {
         switch (connectCount++) {
           case 0:
@@ -346,28 +348,30 @@ describe('MQTT 5.0', function () {
       })
       serverClient.on('publish', function (packet) {
         switch (publishCount++) {
-          case 0:
+          case 0: {
             assert.strictEqual(packet.topic, 'test1')
-            var alias1
+            let alias1
             if (packet.properties) {
               alias1 = packet.properties.topicAlias
             }
             assert.strictEqual(alias1, undefined)
             assert.strictEqual(packet.qos, 1)
-            serverClient.puback({messageId: packet.messageId})
+            serverClient.puback({ messageId: packet.messageId })
             break
-          case 1:
+          }
+          case 1: {
             assert.strictEqual(packet.topic, 'test1')
-            var alias2
+            let alias2
             if (packet.properties) {
               alias2 = packet.properties.topicAlias
             }
             assert.strictEqual(alias2, undefined)
             assert.strictEqual(packet.qos, 0)
             break
-          case 2:
+          }
+          case 2: {
             assert.strictEqual(packet.topic, 'test1')
-            var alias3
+            let alias3
             if (packet.properties) {
               alias3 = packet.properties.topicAlias
             }
@@ -376,6 +380,7 @@ describe('MQTT 5.0', function () {
             server103.close()
             client.end(true, done)
             break
+          }
         }
       })
     }).listen(ports.PORTAND103)
@@ -392,13 +397,13 @@ describe('MQTT 5.0', function () {
   it('should error cb call if PUBLISH out of range topicAlias', function (done) {
     this.timeout(15000)
 
-    var opts = {
+    const opts = {
       host: 'localhost',
       port: ports.PORTAND103,
       protocolVersion: 5
     }
-    var client = mqtt.connect(opts)
-    var server103 = new MqttServer(function (serverClient) {
+    const client = mqtt.connect(opts)
+    const server103 = new MqttServer(function (serverClient) {
       serverClient.on('connect', function (packet) {
         serverClient.connack({
           reasonCode: 0,
@@ -427,13 +432,13 @@ describe('MQTT 5.0', function () {
   it('should error cb call if PUBLISH out of range topicAlias on topicAlias disabled by broker', function (done) {
     this.timeout(15000)
 
-    var opts = {
+    const opts = {
       host: 'localhost',
       port: ports.PORTAND103,
       protocolVersion: 5
     }
-    var client = mqtt.connect(opts)
-    var server103 = new MqttServer(function (serverClient) {
+    const client = mqtt.connect(opts)
+    const server103 = new MqttServer(function (serverClient) {
       serverClient.on('connect', function (packet) {
         serverClient.connack({
           reasonCode: 0,
@@ -459,14 +464,14 @@ describe('MQTT 5.0', function () {
   it('should throw an error if broker PUBLISH out of range topicAlias', function (done) {
     this.timeout(15000)
 
-    var opts = {
+    const opts = {
       host: 'localhost',
       port: ports.PORTAND103,
       protocolVersion: 5,
       topicAliasMaximum: 3
     }
-    var client = mqtt.connect(opts)
-    var server103 = new MqttServer(function (serverClient) {
+    const client = mqtt.connect(opts)
+    const server103 = new MqttServer(function (serverClient) {
       serverClient.on('connect', function (packet) {
         serverClient.connack({
           reasonCode: 0,
@@ -493,14 +498,14 @@ describe('MQTT 5.0', function () {
   it('should throw an error if broker PUBLISH topicAlias:0', function (done) {
     this.timeout(15000)
 
-    var opts = {
+    const opts = {
       host: 'localhost',
       port: ports.PORTAND103,
       protocolVersion: 5,
       topicAliasMaximum: 3
     }
-    var client = mqtt.connect(opts)
-    var server103 = new MqttServer(function (serverClient) {
+    const client = mqtt.connect(opts)
+    const server103 = new MqttServer(function (serverClient) {
       serverClient.on('connect', function (packet) {
         serverClient.connack({
           reasonCode: 0,
@@ -527,14 +532,14 @@ describe('MQTT 5.0', function () {
   it('should throw an error if broker PUBLISH unregistered topicAlias', function (done) {
     this.timeout(15000)
 
-    var opts = {
+    const opts = {
       host: 'localhost',
       port: ports.PORTAND103,
       protocolVersion: 5,
       topicAliasMaximum: 3
     }
-    var client = mqtt.connect(opts)
-    var server103 = new MqttServer(function (serverClient) {
+    const client = mqtt.connect(opts)
+    const server103 = new MqttServer(function (serverClient) {
       serverClient.on('connect', function (packet) {
         serverClient.connack({
           reasonCode: 0,
@@ -560,10 +565,9 @@ describe('MQTT 5.0', function () {
 
   it('should throw an error if there is Auth Data with no Auth Method', function (done) {
     this.timeout(5000)
-    var client
-    var opts = {host: 'localhost', port: ports.PORTAND115, protocolVersion: 5, properties: { authenticationData: Buffer.from([1, 2, 3, 4]) }}
+    const opts = { host: 'localhost', port: ports.PORTAND115, protocolVersion: 5, properties: { authenticationData: Buffer.from([1, 2, 3, 4]) } }
     console.log('client connecting')
-    client = mqtt.connect(opts)
+    const client = mqtt.connect(opts)
     client.on('error', function (error) {
       console.log('error hit')
       assert.strictEqual(error.message, 'Packet has no Authentication Method')
@@ -582,15 +586,15 @@ describe('MQTT 5.0', function () {
         serverClient.end(done)
       })
     })
-    var opts = {host: 'localhost', port: ports.PORTAND115, protocolVersion: 5, properties: { authenticationMethod: 'json' }, authPacket: {}}
+    const opts = { host: 'localhost', port: ports.PORTAND115, protocolVersion: 5, properties: { authenticationMethod: 'json' }, authPacket: {} }
     console.log('calling mqtt connect')
     mqtt.connect(opts)
   })
 
   it('Maximum Packet Size', function (done) {
     this.timeout(15000)
-    var opts = {host: 'localhost', port: ports.PORTAND115, protocolVersion: 5, properties: { maximumPacketSize: 1 }}
-    var client = mqtt.connect(opts)
+    const opts = { host: 'localhost', port: ports.PORTAND115, protocolVersion: 5, properties: { maximumPacketSize: 1 } }
+    const client = mqtt.connect(opts)
     client.on('error', function (error) {
       assert.strictEqual(error.message, 'exceeding packets size connack')
       client.end(true, done)
@@ -599,7 +603,7 @@ describe('MQTT 5.0', function () {
 
   it('Change values of some properties by server response', function (done) {
     this.timeout(15000)
-    var server116 = new MqttServer(function (serverClient) {
+    const server116 = new MqttServer(function (serverClient) {
       serverClient.on('connect', function (packet) {
         serverClient.connack({
           reasonCode: 0,
@@ -610,7 +614,7 @@ describe('MQTT 5.0', function () {
         })
       })
     }).listen(ports.PORTAND116)
-    var opts = {
+    const opts = {
       host: 'localhost',
       port: ports.PORTAND116,
       protocolVersion: 5,
@@ -620,7 +624,7 @@ describe('MQTT 5.0', function () {
         maximumPacketSize: 100
       }
     }
-    var client = mqtt.connect(opts)
+    const client = mqtt.connect(opts)
     client.on('connect', function () {
       assert.strictEqual(client.options.keepalive, 16)
       assert.strictEqual(client.options.properties.maximumPacketSize, 95)
@@ -631,9 +635,9 @@ describe('MQTT 5.0', function () {
 
   it('should resubscribe when reconnecting with protocolVersion 5 and Session Present flag is false', function (done) {
     this.timeout(15000)
-    var tryReconnect = true
-    var reconnectEvent = false
-    var server316 = new MqttServer(function (serverClient) {
+    let tryReconnect = true
+    let reconnectEvent = false
+    const server316 = new MqttServer(function (serverClient) {
       serverClient.on('connect', function (packet) {
         serverClient.connack({
           reasonCode: 0,
@@ -647,12 +651,12 @@ describe('MQTT 5.0', function () {
         })
       })
     }).listen(ports.PORTAND316)
-    var opts = {
+    const opts = {
       host: 'localhost',
       port: ports.PORTAND316,
       protocolVersion: 5
     }
-    var client = mqtt.connect(opts)
+    const client = mqtt.connect(opts)
 
     client.on('reconnect', function () {
       reconnectEvent = true
@@ -674,9 +678,9 @@ describe('MQTT 5.0', function () {
 
   it('should resubscribe when reconnecting with protocolVersion 5 and properties', function (done) {
     // this.timeout(15000)
-    var tryReconnect = true
-    var reconnectEvent = false
-    var server326 = new MqttServer(function (serverClient) {
+    let tryReconnect = true
+    let reconnectEvent = false
+    const server326 = new MqttServer(function (serverClient) {
       serverClient.on('connect', function (packet) {
         serverClient.connack({
           reasonCode: 0,
@@ -701,12 +705,12 @@ describe('MQTT 5.0', function () {
       })
     }).listen(ports.PORTAND326)
 
-    var opts = {
+    const opts = {
       host: 'localhost',
       port: ports.PORTAND326,
       protocolVersion: 5
     }
-    var client = mqtt.connect(opts)
+    const client = mqtt.connect(opts)
 
     client.on('reconnect', function () {
       reconnectEvent = true
@@ -726,7 +730,7 @@ describe('MQTT 5.0', function () {
     })
   })
 
-  var serverThatSendsErrors = new MqttServer(function (serverClient) {
+  const serverThatSendsErrors = new MqttServer(function (serverClient) {
     serverClient.on('connect', function (packet) {
       serverClient.connack({
         reasonCode: 0
@@ -760,13 +764,13 @@ describe('MQTT 5.0', function () {
 
   it('Subscribe properties', function (done) {
     this.timeout(15000)
-    var opts = {
+    const opts = {
       host: 'localhost',
       port: ports.PORTAND119,
       protocolVersion: 5
     }
-    var subOptions = { properties: { subscriptionIdentifier: 1234 } }
-    var server119 = new MqttServer(function (serverClient) {
+    const subOptions = { properties: { subscriptionIdentifier: 1234 } }
+    const server119 = new MqttServer(function (serverClient) {
       serverClient.on('connect', function (packet) {
         serverClient.connack({
           reasonCode: 0
@@ -780,7 +784,7 @@ describe('MQTT 5.0', function () {
       })
     }).listen(ports.PORTAND119)
 
-    var client = mqtt.connect(opts)
+    const client = mqtt.connect(opts)
     client.on('connect', function () {
       client.subscribe('a/b', subOptions)
     })
@@ -789,14 +793,14 @@ describe('MQTT 5.0', function () {
   it('puback handling errors check', function (done) {
     this.timeout(15000)
     serverThatSendsErrors.listen(ports.PORTAND117)
-    var opts = {
+    const opts = {
       host: 'localhost',
       port: ports.PORTAND117,
       protocolVersion: 5
     }
-    var client = mqtt.connect(opts)
+    const client = mqtt.connect(opts)
     client.once('connect', () => {
-      client.publish('a/b', 'message', {qos: 1}, function (err, packet) {
+      client.publish('a/b', 'message', { qos: 1 }, function (err, packet) {
         assert.strictEqual(err.message, 'Publish error: Session taken over')
         assert.strictEqual(err.code, 142)
       })
@@ -808,14 +812,14 @@ describe('MQTT 5.0', function () {
   it('pubrec handling errors check', function (done) {
     this.timeout(15000)
     serverThatSendsErrors.listen(ports.PORTAND118)
-    var opts = {
+    const opts = {
       host: 'localhost',
       port: ports.PORTAND118,
       protocolVersion: 5
     }
-    var client = mqtt.connect(opts)
+    const client = mqtt.connect(opts)
     client.once('connect', () => {
-      client.publish('a/b', 'message', {qos: 2}, function (err, packet) {
+      client.publish('a/b', 'message', { qos: 2 }, function (err, packet) {
         assert.strictEqual(err.message, 'Publish error: Session taken over')
         assert.strictEqual(err.code, 142)
       })
@@ -827,12 +831,12 @@ describe('MQTT 5.0', function () {
   it('puback handling custom reason code', function (done) {
     // this.timeout(15000)
     serverThatSendsErrors.listen(ports.PORTAND117)
-    var opts = {
+    const opts = {
       host: 'localhost',
       port: ports.PORTAND117,
       protocolVersion: 5,
       customHandleAcks: function (topic, message, packet, cb) {
-        var code = 0
+        let code = 0
         if (topic === 'a/b') {
           code = 128
         }
@@ -853,31 +857,31 @@ describe('MQTT 5.0', function () {
       })
     })
 
-    var client = mqtt.connect(opts)
+    const client = mqtt.connect(opts)
     client.once('connect', function () {
-      client.subscribe('a/b', {qos: 1})
+      client.subscribe('a/b', { qos: 1 })
     })
   })
 
   it('server side disconnect', function (done) {
     this.timeout(15000)
-    var server327 = new MqttServer(function (serverClient) {
+    const server327 = new MqttServer(function (serverClient) {
       serverClient.on('connect', function (packet) {
         serverClient.connack({
           reasonCode: 0
         })
-        serverClient.disconnect({reasonCode: 128})
+        serverClient.disconnect({ reasonCode: 128 })
         server327.close()
       })
     })
     server327.listen(ports.PORTAND327)
-    var opts = {
+    const opts = {
       host: 'localhost',
       port: ports.PORTAND327,
       protocolVersion: 5
     }
 
-    var client = mqtt.connect(opts)
+    const client = mqtt.connect(opts)
     client.once('disconnect', function (disconnectPacket) {
       assert.strictEqual(disconnectPacket.reasonCode, 128)
       client.end(true, done)
@@ -887,12 +891,12 @@ describe('MQTT 5.0', function () {
   it('pubrec handling custom reason code', function (done) {
     this.timeout(15000)
     serverThatSendsErrors.listen(ports.PORTAND117)
-    var opts = {
+    const opts = {
       host: 'localhost',
       port: ports.PORTAND117,
       protocolVersion: 5,
       customHandleAcks: function (topic, message, packet, cb) {
-        var code = 0
+        let code = 0
         if (topic === 'a/b') {
           code = 128
         }
@@ -913,21 +917,21 @@ describe('MQTT 5.0', function () {
       })
     })
 
-    var client = mqtt.connect(opts)
+    const client = mqtt.connect(opts)
     client.once('connect', function () {
-      client.subscribe('a/b', {qos: 1})
+      client.subscribe('a/b', { qos: 1 })
     })
   })
 
   it('puback handling custom reason code with error', function (done) {
     this.timeout(15000)
     serverThatSendsErrors.listen(ports.PORTAND117)
-    var opts = {
+    const opts = {
       host: 'localhost',
       port: ports.PORTAND117,
       protocolVersion: 5,
       customHandleAcks: function (topic, message, packet, cb) {
-        var code = 0
+        const code = 0
         if (topic === 'a/b') {
           cb(new Error('a/b is not valid'))
         }
@@ -941,26 +945,26 @@ describe('MQTT 5.0', function () {
       })
     })
 
-    var client = mqtt.connect(opts)
+    const client = mqtt.connect(opts)
     client.on('error', function (error) {
       assert.strictEqual(error.message, 'a/b is not valid')
       client.end(true, done)
       serverThatSendsErrors.close()
     })
     client.once('connect', function () {
-      client.subscribe('a/b', {qos: 1})
+      client.subscribe('a/b', { qos: 1 })
     })
   })
 
   it('pubrec handling custom reason code with error', function (done) {
     this.timeout(15000)
     serverThatSendsErrors.listen(ports.PORTAND117)
-    var opts = {
+    const opts = {
       host: 'localhost',
       port: ports.PORTAND117,
       protocolVersion: 5,
       customHandleAcks: function (topic, message, packet, cb) {
-        var code = 0
+        const code = 0
         if (topic === 'a/b') {
           cb(new Error('a/b is not valid'))
         }
@@ -974,26 +978,26 @@ describe('MQTT 5.0', function () {
       })
     })
 
-    var client = mqtt.connect(opts)
+    const client = mqtt.connect(opts)
     client.on('error', function (error) {
       assert.strictEqual(error.message, 'a/b is not valid')
       client.end(true, done)
       serverThatSendsErrors.close()
     })
     client.once('connect', function () {
-      client.subscribe('a/b', {qos: 1})
+      client.subscribe('a/b', { qos: 1 })
     })
   })
 
   it('puback handling custom invalid reason code', function (done) {
     this.timeout(15000)
     serverThatSendsErrors.listen(ports.PORTAND117)
-    var opts = {
+    const opts = {
       host: 'localhost',
       port: ports.PORTAND117,
       protocolVersion: 5,
       customHandleAcks: function (topic, message, packet, cb) {
-        var code = 0
+        let code = 0
         if (topic === 'a/b') {
           code = 124124
         }
@@ -1007,26 +1011,26 @@ describe('MQTT 5.0', function () {
       })
     })
 
-    var client = mqtt.connect(opts)
+    const client = mqtt.connect(opts)
     client.on('error', function (error) {
       assert.strictEqual(error.message, 'Wrong reason code for puback')
       client.end(true, done)
       serverThatSendsErrors.close()
     })
     client.once('connect', function () {
-      client.subscribe('a/b', {qos: 1})
+      client.subscribe('a/b', { qos: 1 })
     })
   })
 
   it('pubrec handling custom invalid reason code', function (done) {
     this.timeout(15000)
     serverThatSendsErrors.listen(ports.PORTAND117)
-    var opts = {
+    const opts = {
       host: 'localhost',
       port: ports.PORTAND117,
       protocolVersion: 5,
       customHandleAcks: function (topic, message, packet, cb) {
-        var code = 0
+        let code = 0
         if (topic === 'a/b') {
           code = 34535
         }
@@ -1040,14 +1044,14 @@ describe('MQTT 5.0', function () {
       })
     })
 
-    var client = mqtt.connect(opts)
+    const client = mqtt.connect(opts)
     client.on('error', function (error) {
       assert.strictEqual(error.message, 'Wrong reason code for pubrec')
       client.end(true, done)
       serverThatSendsErrors.close()
     })
     client.once('connect', function () {
-      client.subscribe('a/b', {qos: 1})
+      client.subscribe('a/b', { qos: 1 })
     })
   })
 })
diff --git a/test/helpers/port_list.js b/test/helpers/port_list.js
index dc77ef07a..27138954b 100644
--- a/test/helpers/port_list.js
+++ b/test/helpers/port_list.js
@@ -1,27 +1,27 @@
-var PORT = 9876
-var PORTAND40 = PORT + 40
-var PORTAND41 = PORT + 41
-var PORTAND42 = PORT + 42
-var PORTAND43 = PORT + 43
-var PORTAND44 = PORT + 44
-var PORTAND45 = PORT + 45
-var PORTAND46 = PORT + 46
-var PORTAND47 = PORT + 47
-var PORTAND48 = PORT + 48
-var PORTAND49 = PORT + 49
-var PORTAND50 = PORT + 50
-var PORTAND72 = PORT + 72
-var PORTAND103 = PORT + 103
-var PORTAND114 = PORT + 114
-var PORTAND115 = PORT + 115
-var PORTAND116 = PORT + 116
-var PORTAND117 = PORT + 117
-var PORTAND118 = PORT + 118
-var PORTAND119 = PORT + 119
-var PORTAND316 = PORT + 316
-var PORTAND326 = PORT + 326
-var PORTAND327 = PORT + 327
-var PORTAND400 = PORT + 400
+const PORT = 9876
+const PORTAND40 = PORT + 40
+const PORTAND41 = PORT + 41
+const PORTAND42 = PORT + 42
+const PORTAND43 = PORT + 43
+const PORTAND44 = PORT + 44
+const PORTAND45 = PORT + 45
+const PORTAND46 = PORT + 46
+const PORTAND47 = PORT + 47
+const PORTAND48 = PORT + 48
+const PORTAND49 = PORT + 49
+const PORTAND50 = PORT + 50
+const PORTAND72 = PORT + 72
+const PORTAND103 = PORT + 103
+const PORTAND114 = PORT + 114
+const PORTAND115 = PORT + 115
+const PORTAND116 = PORT + 116
+const PORTAND117 = PORT + 117
+const PORTAND118 = PORT + 118
+const PORTAND119 = PORT + 119
+const PORTAND316 = PORT + 316
+const PORTAND326 = PORT + 326
+const PORTAND327 = PORT + 327
+const PORTAND400 = PORT + 400
 
 module.exports = {
   PORT,
diff --git a/test/helpers/server.js b/test/helpers/server.js
index 46bd79537..aae053517 100644
--- a/test/helpers/server.js
+++ b/test/helpers/server.js
@@ -1,11 +1,11 @@
 'use strict'
 
-var MqttServer = require('../server').MqttServer
-var MqttSecureServer = require('../server').MqttSecureServer
-var fs = require('fs')
+const MqttServer = require('../server').MqttServer
+const MqttSecureServer = require('../server').MqttSecureServer
+const fs = require('fs')
 
 module.exports.init_server = function (PORT) {
-  var server = new MqttServer(function (client) {
+  const server = new MqttServer(function (client) {
     client.on('connect', function () {
       client.connack(0)
     })
@@ -13,10 +13,10 @@ module.exports.init_server = function (PORT) {
     client.on('publish', function (packet) {
       switch (packet.qos) {
         case 1:
-          client.puback({messageId: packet.messageId})
+          client.puback({ messageId: packet.messageId })
           break
         case 2:
-          client.pubrec({messageId: packet.messageId})
+          client.pubrec({ messageId: packet.messageId })
           break
         default:
           break
@@ -24,7 +24,7 @@ module.exports.init_server = function (PORT) {
     })
 
     client.on('pubrel', function (packet) {
-      client.pubcomp({messageId: packet.messageId})
+      client.pubcomp({ messageId: packet.messageId })
     })
 
     client.on('pingreq', function () {
@@ -40,12 +40,12 @@ module.exports.init_server = function (PORT) {
 }
 
 module.exports.init_secure_server = function (port, key, cert) {
-  var server = new MqttSecureServer({
+  const server = new MqttSecureServer({
     key: fs.readFileSync(key),
     cert: fs.readFileSync(cert)
   }, function (client) {
     client.on('connect', function () {
-      client.connack({returnCode: 0})
+      client.connack({ returnCode: 0 })
     })
   })
   server.listen(port)
diff --git a/test/helpers/server_process.js b/test/helpers/server_process.js
index 1d1095cb3..0875cd9da 100644
--- a/test/helpers/server_process.js
+++ b/test/helpers/server_process.js
@@ -1,6 +1,6 @@
 'use strict'
 
-var MqttServer = require('../server').MqttServer
+const MqttServer = require('../server').MqttServer
 
 new MqttServer(function (client) {
   client.on('connect', function () {
diff --git a/test/message-id-provider.js b/test/message-id-provider.js
index 2f84bdf35..3d359def3 100644
--- a/test/message-id-provider.js
+++ b/test/message-id-provider.js
@@ -1,12 +1,12 @@
 'use strict'
-var assert = require('chai').assert
-var DefaultMessageIdProvider = require('../lib/default-message-id-provider')
-var UniqueMessageIdProvider = require('../lib/unique-message-id-provider')
+const assert = require('chai').assert
+const DefaultMessageIdProvider = require('../lib/default-message-id-provider')
+const UniqueMessageIdProvider = require('../lib/unique-message-id-provider')
 
 describe('message id provider', function () {
   describe('default', function () {
     it('should return 1 once the internal counter reached limit', function () {
-      var provider = new DefaultMessageIdProvider()
+      const provider = new DefaultMessageIdProvider()
       provider.nextId = 65535
 
       assert.equal(provider.allocate(), 65535)
@@ -14,7 +14,7 @@ describe('message id provider', function () {
     })
 
     it('should return 65535 for last message id once the internal counter reached limit', function () {
-      var provider = new DefaultMessageIdProvider()
+      const provider = new DefaultMessageIdProvider()
       provider.nextId = 65535
 
       assert.equal(provider.allocate(), 65535)
@@ -23,32 +23,32 @@ describe('message id provider', function () {
       assert.equal(provider.getLastAllocated(), 1)
     })
     it('should return true when register with non allocated messageId', function () {
-      var provider = new DefaultMessageIdProvider()
+      const provider = new DefaultMessageIdProvider()
       assert.equal(provider.register(10), true)
     })
   })
   describe('unique', function () {
     it('should return 1, 2, 3..,  when allocate', function () {
-      var provider = new UniqueMessageIdProvider()
+      const provider = new UniqueMessageIdProvider()
       assert.equal(provider.allocate(), 1)
       assert.equal(provider.allocate(), 2)
       assert.equal(provider.allocate(), 3)
     })
     it('should skip registerd messageId', function () {
-      var provider = new UniqueMessageIdProvider()
+      const provider = new UniqueMessageIdProvider()
       assert.equal(provider.register(2), true)
       assert.equal(provider.allocate(), 1)
       assert.equal(provider.allocate(), 3)
     })
     it('should return false register allocated  messageId', function () {
-      var provider = new UniqueMessageIdProvider()
+      const provider = new UniqueMessageIdProvider()
       assert.equal(provider.allocate(), 1)
       assert.equal(provider.register(1), false)
       assert.equal(provider.register(5), true)
       assert.equal(provider.register(5), false)
     })
     it('should retrun correct last messageId', function () {
-      var provider = new UniqueMessageIdProvider()
+      const provider = new UniqueMessageIdProvider()
       assert.equal(provider.allocate(), 1)
       assert.equal(provider.getLastAllocated(), 1)
       assert.equal(provider.register(2), true)
@@ -57,7 +57,7 @@ describe('message id provider', function () {
       assert.equal(provider.getLastAllocated(), 3)
     })
     it('should be reusable deallocated messageId', function () {
-      var provider = new UniqueMessageIdProvider()
+      const provider = new UniqueMessageIdProvider()
       assert.equal(provider.allocate(), 1)
       assert.equal(provider.allocate(), 2)
       assert.equal(provider.allocate(), 3)
@@ -65,8 +65,8 @@ describe('message id provider', function () {
       assert.equal(provider.allocate(), 2)
     })
     it('should allocate all messageId and then return null', function () {
-      var provider = new UniqueMessageIdProvider()
-      for (var i = 1; i <= 65535; i++) {
+      const provider = new UniqueMessageIdProvider()
+      for (let i = 1; i <= 65535; i++) {
         assert.equal(provider.allocate(), i)
       }
       assert.equal(provider.allocate(), null)
@@ -75,14 +75,13 @@ describe('message id provider', function () {
       assert.equal(provider.allocate(), null)
     })
     it('should all messageId reallocatable after clear', function () {
-      var provider = new UniqueMessageIdProvider()
-      var i
-      for (i = 1; i <= 65535; i++) {
+      const provider = new UniqueMessageIdProvider()
+      for (let i = 1; i <= 65535; i++) {
         assert.equal(provider.allocate(), i)
       }
       assert.equal(provider.allocate(), null)
       provider.clear()
-      for (i = 1; i <= 65535; i++) {
+      for (let i = 1; i <= 65535; i++) {
         assert.equal(provider.allocate(), i)
       }
       assert.equal(provider.allocate(), null)
diff --git a/test/mqtt.js b/test/mqtt.js
index f55d04a33..ab79cabd1 100644
--- a/test/mqtt.js
+++ b/test/mqtt.js
@@ -1,14 +1,13 @@
 'use strict'
 
-var fs = require('fs')
-var path = require('path')
-var mqtt = require('../')
+const fs = require('fs')
+const path = require('path')
+const mqtt = require('../')
 
 describe('mqtt', function () {
   describe('#connect', function () {
-    var sslOpts, sslOpts2
     it('should return an MqttClient when connect is called with mqtt:/ url', function () {
-      var c = mqtt.connect('mqtt://localhost:1883')
+      const c = mqtt.connect('mqtt://localhost:1883')
 
       c.should.be.instanceOf(mqtt.MqttClient)
       c.end()
@@ -16,20 +15,20 @@ describe('mqtt', function () {
 
     it('should throw an error when called with no protocol specified', function () {
       (function () {
-        var c = mqtt.connect('foo.bar.com')
+        const c = mqtt.connect('foo.bar.com')
         c.end()
       }).should.throw('Missing protocol')
     })
 
     it('should throw an error when called with no protocol specified - with options', function () {
       (function () {
-        var c = mqtt.connect('tcp://foo.bar.com', { protocol: null })
+        const c = mqtt.connect('tcp://foo.bar.com', { protocol: null })
         c.end()
       }).should.throw('Missing protocol')
     })
 
     it('should return an MqttClient with username option set', function () {
-      var c = mqtt.connect('mqtt://user:pass@localhost:1883')
+      const c = mqtt.connect('mqtt://user:pass@localhost:1883')
 
       c.should.be.instanceOf(mqtt.MqttClient)
       c.options.should.have.property('username', 'user')
@@ -38,7 +37,7 @@ describe('mqtt', function () {
     })
 
     it('should return an MqttClient with username and password options set', function () {
-      var c = mqtt.connect('mqtt://user@localhost:1883')
+      const c = mqtt.connect('mqtt://user@localhost:1883')
 
       c.should.be.instanceOf(mqtt.MqttClient)
       c.options.should.have.property('username', 'user')
@@ -46,7 +45,7 @@ describe('mqtt', function () {
     })
 
     it('should return an MqttClient with the clientid with random value', function () {
-      var c = mqtt.connect('mqtt://user@localhost:1883')
+      const c = mqtt.connect('mqtt://user@localhost:1883')
 
       c.should.be.instanceOf(mqtt.MqttClient)
       c.options.should.have.property('clientId')
@@ -54,7 +53,7 @@ describe('mqtt', function () {
     })
 
     it('should return an MqttClient with the clientid with empty string', function () {
-      var c = mqtt.connect('mqtt://user@localhost:1883?clientId=')
+      const c = mqtt.connect('mqtt://user@localhost:1883?clientId=')
 
       c.should.be.instanceOf(mqtt.MqttClient)
       c.options.should.have.property('clientId', '')
@@ -62,7 +61,7 @@ describe('mqtt', function () {
     })
 
     it('should return an MqttClient with the clientid option set', function () {
-      var c = mqtt.connect('mqtt://user@localhost:1883?clientId=123')
+      const c = mqtt.connect('mqtt://user@localhost:1883?clientId=123')
 
       c.should.be.instanceOf(mqtt.MqttClient)
       c.options.should.have.property('clientId', '123')
@@ -70,28 +69,28 @@ describe('mqtt', function () {
     })
 
     it('should return an MqttClient when connect is called with tcp:/ url', function () {
-      var c = mqtt.connect('tcp://localhost')
+      const c = mqtt.connect('tcp://localhost')
 
       c.should.be.instanceOf(mqtt.MqttClient)
       c.end()
     })
 
     it('should return an MqttClient with correct host when called with a host and port', function () {
-      var c = mqtt.connect('tcp://user:pass@localhost:1883')
+      const c = mqtt.connect('tcp://user:pass@localhost:1883')
 
       c.options.should.have.property('hostname', 'localhost')
       c.options.should.have.property('port', 1883)
       c.end()
     })
 
-    sslOpts = {
+    const sslOpts = {
       keyPath: path.join(__dirname, 'helpers', 'private-key.pem'),
       certPath: path.join(__dirname, 'helpers', 'public-cert.pem'),
       caPaths: [path.join(__dirname, 'helpers', 'public-cert.pem')]
     }
 
     it('should return an MqttClient when connect is called with mqtts:/ url', function () {
-      var c = mqtt.connect('mqtts://localhost', sslOpts)
+      const c = mqtt.connect('mqtts://localhost', sslOpts)
 
       c.options.should.have.property('protocol', 'mqtts')
 
@@ -102,7 +101,7 @@ describe('mqtt', function () {
     })
 
     it('should return an MqttClient when connect is called with ssl:/ url', function () {
-      var c = mqtt.connect('ssl://localhost', sslOpts)
+      const c = mqtt.connect('ssl://localhost', sslOpts)
 
       c.options.should.have.property('protocol', 'ssl')
 
@@ -113,7 +112,7 @@ describe('mqtt', function () {
     })
 
     it('should return an MqttClient when connect is called with ws:/ url', function () {
-      var c = mqtt.connect('ws://localhost', sslOpts)
+      const c = mqtt.connect('ws://localhost', sslOpts)
 
       c.options.should.have.property('protocol', 'ws')
 
@@ -124,7 +123,7 @@ describe('mqtt', function () {
     })
 
     it('should return an MqttClient when connect is called with wss:/ url', function () {
-      var c = mqtt.connect('wss://localhost', sslOpts)
+      const c = mqtt.connect('wss://localhost', sslOpts)
 
       c.options.should.have.property('protocol', 'wss')
 
@@ -134,7 +133,7 @@ describe('mqtt', function () {
       c.end()
     })
 
-    sslOpts2 = {
+    const sslOpts2 = {
       key: fs.readFileSync(path.join(__dirname, 'helpers', 'private-key.pem')),
       cert: fs.readFileSync(path.join(__dirname, 'helpers', 'public-cert.pem')),
       ca: [fs.readFileSync(path.join(__dirname, 'helpers', 'public-cert.pem'))]
@@ -143,7 +142,7 @@ describe('mqtt', function () {
     it('should throw an error when it is called with cert and key set but no protocol specified', function () {
       // to do rewrite wrap function
       (function () {
-        var c = mqtt.connect(sslOpts2)
+        const c = mqtt.connect(sslOpts2)
         c.end()
       }).should.throw('Missing secure protocol key')
     })
@@ -151,14 +150,14 @@ describe('mqtt', function () {
     it('should throw an error when it is called with cert and key set and protocol other than allowed: mqtt,mqtts,ws,wss,wxs', function () {
       (function () {
         sslOpts2.protocol = 'UNKNOWNPROTOCOL'
-        var c = mqtt.connect(sslOpts2)
+        const c = mqtt.connect(sslOpts2)
         c.end()
       }).should.throw()
     })
 
     it('should return a MqttClient with mqtts set when connect is called key and cert set and protocol mqtt', function () {
       sslOpts2.protocol = 'mqtt'
-      var c = mqtt.connect(sslOpts2)
+      const c = mqtt.connect(sslOpts2)
 
       c.options.should.have.property('protocol', 'mqtts')
 
@@ -169,7 +168,7 @@ describe('mqtt', function () {
 
     it('should return a MqttClient with mqtts set when connect is called key and cert set and protocol mqtts', function () {
       sslOpts2.protocol = 'mqtts'
-      var c = mqtt.connect(sslOpts2)
+      const c = mqtt.connect(sslOpts2)
 
       c.options.should.have.property('protocol', 'mqtts')
 
@@ -180,7 +179,7 @@ describe('mqtt', function () {
 
     it('should return a MqttClient with wss set when connect is called key and cert set and protocol ws', function () {
       sslOpts2.protocol = 'ws'
-      var c = mqtt.connect(sslOpts2)
+      const c = mqtt.connect(sslOpts2)
 
       c.options.should.have.property('protocol', 'wss')
 
@@ -191,7 +190,7 @@ describe('mqtt', function () {
 
     it('should return a MqttClient with wss set when connect is called key and cert set and protocol wss', function () {
       sslOpts2.protocol = 'wss'
-      var c = mqtt.connect(sslOpts2)
+      const c = mqtt.connect(sslOpts2)
 
       c.options.should.have.property('protocol', 'wss')
 
@@ -201,7 +200,7 @@ describe('mqtt', function () {
     })
 
     it('should return an MqttClient with the clientid with option of clientId as empty string', function () {
-      var c = mqtt.connect('mqtt://localhost:1883', {
+      const c = mqtt.connect('mqtt://localhost:1883', {
         clientId: ''
       })
 
@@ -210,7 +209,7 @@ describe('mqtt', function () {
     })
 
     it('should return an MqttClient with the clientid with option of clientId empty', function () {
-      var c = mqtt.connect('mqtt://localhost:1883')
+      const c = mqtt.connect('mqtt://localhost:1883')
 
       c.should.be.instanceOf(mqtt.MqttClient)
       c.options.should.have.property('clientId')
@@ -218,7 +217,7 @@ describe('mqtt', function () {
     })
 
     it('should return an MqttClient with the clientid with option of with specific clientId', function () {
-      var c = mqtt.connect('mqtt://localhost:1883', {
+      const c = mqtt.connect('mqtt://localhost:1883', {
         clientId: '123'
       })
 
diff --git a/test/mqtt_store.js b/test/mqtt_store.js
index 976a01aff..62c2f7d47 100644
--- a/test/mqtt_store.js
+++ b/test/mqtt_store.js
@@ -1,6 +1,6 @@
 'use strict'
 
-var mqtt = require('../lib/connect')
+const mqtt = require('../lib/connect')
 
 describe('store in lib/connect/index.js (webpack entry point)', function () {
   it('should create store', function (done) {
diff --git a/test/secure_client.js b/test/secure_client.js
index 95b7a6197..90d748d3c 100644
--- a/test/secure_client.js
+++ b/test/secure_client.js
@@ -1,24 +1,24 @@
 'use strict'
 
-var mqtt = require('..')
-var path = require('path')
-var abstractClientTests = require('./abstract_client')
-var fs = require('fs')
-var port = 9899
-var KEY = path.join(__dirname, 'helpers', 'tls-key.pem')
-var CERT = path.join(__dirname, 'helpers', 'tls-cert.pem')
-var WRONG_CERT = path.join(__dirname, 'helpers', 'wrong-cert.pem')
-var MqttSecureServer = require('./server').MqttSecureServer
-var assert = require('chai').assert
-
-var serverListener = function (client) {
+const mqtt = require('..')
+const path = require('path')
+const abstractClientTests = require('./abstract_client')
+const fs = require('fs')
+const port = 9899
+const KEY = path.join(__dirname, 'helpers', 'tls-key.pem')
+const CERT = path.join(__dirname, 'helpers', 'tls-cert.pem')
+const WRONG_CERT = path.join(__dirname, 'helpers', 'wrong-cert.pem')
+const MqttSecureServer = require('./server').MqttSecureServer
+const assert = require('chai').assert
+
+const serverListener = function (client) {
   // this is the Server's MQTT Client
   client.on('connect', function (packet) {
     if (packet.clientId === 'invalid') {
-      client.connack({returnCode: 2})
+      client.connack({ returnCode: 2 })
     } else {
       server.emit('connect', client)
-      client.connack({returnCode: 0})
+      client.connack({ returnCode: 0 })
     }
   })
 
@@ -70,18 +70,18 @@ var serverListener = function (client) {
   })
 }
 
-var server = new MqttSecureServer({
+const server = new MqttSecureServer({
   key: fs.readFileSync(KEY),
   cert: fs.readFileSync(CERT)
 }, serverListener).listen(port)
 
 describe('MqttSecureClient', function () {
-  var config = { protocol: 'mqtts', port: port, rejectUnauthorized: false }
+  const config = { protocol: 'mqtts', port: port, rejectUnauthorized: false }
   abstractClientTests(server, config)
 
   describe('with secure parameters', function () {
     it('should validate successfully the CA', function (done) {
-      var client = mqtt.connect({
+      const client = mqtt.connect({
         protocol: 'mqtts',
         port: port,
         ca: [fs.readFileSync(CERT)],
@@ -98,7 +98,7 @@ describe('MqttSecureClient', function () {
     })
 
     it('should validate successfully the CA using URI', function (done) {
-      var client = mqtt.connect('mqtts://localhost:' + port, {
+      const client = mqtt.connect('mqtts://localhost:' + port, {
         ca: [fs.readFileSync(CERT)],
         rejectUnauthorized: true
       })
@@ -113,7 +113,7 @@ describe('MqttSecureClient', function () {
     })
 
     it('should validate successfully the CA using URI with path', function (done) {
-      var client = mqtt.connect('mqtts://localhost:' + port + '/', {
+      const client = mqtt.connect('mqtts://localhost:' + port + '/', {
         ca: [fs.readFileSync(CERT)],
         rejectUnauthorized: true
       })
@@ -128,7 +128,7 @@ describe('MqttSecureClient', function () {
     })
 
     it('should validate unsuccessfully the CA', function (done) {
-      var client = mqtt.connect({
+      const client = mqtt.connect({
         protocol: 'mqtts',
         port: port,
         ca: [fs.readFileSync(WRONG_CERT)],
@@ -143,7 +143,7 @@ describe('MqttSecureClient', function () {
     })
 
     it('should emit close on TLS error', function (done) {
-      var client = mqtt.connect({
+      const client = mqtt.connect({
         protocol: 'mqtts',
         port: port,
         ca: [fs.readFileSync(WRONG_CERT)],
@@ -159,15 +159,14 @@ describe('MqttSecureClient', function () {
     })
 
     it('should support SNI on the TLS connection', function (done) {
-      var hostname, client
       server.removeAllListeners('secureConnection') // clear eventHandler
       server.once('secureConnection', function (tlsSocket) { // one time eventHandler
         assert.equal(tlsSocket.servername, hostname) // validate SNI set
         server.setupConnection(tlsSocket)
       })
 
-      hostname = 'localhost'
-      client = mqtt.connect({
+      const hostname = 'localhost'
+      const client = mqtt.connect({
         protocol: 'mqtts',
         port: port,
         ca: [fs.readFileSync(CERT)],
diff --git a/test/server.js b/test/server.js
index ccfe2f4d1..a190444e5 100644
--- a/test/server.js
+++ b/test/server.js
@@ -1,8 +1,8 @@
 'use strict'
 
-var net = require('net')
-var tls = require('tls')
-var Connection = require('mqtt-connection')
+const net = require('net')
+const tls = require('tls')
+const Connection = require('mqtt-connection')
 
 /**
  * MqttServer
@@ -14,10 +14,10 @@ class MqttServer extends net.Server {
     super()
     this.connectionList = []
 
-    var that = this
+    const that = this
     this.on('connection', function (duplex) {
       this.connectionList.push(duplex)
-      var connection = new Connection(duplex, function () {
+      const connection = new Connection(duplex, function () {
         that.emit('client', connection)
       })
     })
@@ -40,7 +40,7 @@ class MqttServerNoWait extends net.Server {
 
     this.on('connection', function (duplex) {
       this.connectionList.push(duplex)
-      var connection = new Connection(duplex)
+      const connection = new Connection(duplex)
       // do not wait for connection to return to send it to the client.
       this.emit('client', connection)
     })
@@ -70,8 +70,8 @@ class MqttSecureServer extends tls.Server {
 
     this.on('secureConnection', function (socket) {
       this.connectionList.push(socket)
-      var that = this
-      var connection = new Connection(socket, function () {
+      const that = this
+      const connection = new Connection(socket, function () {
         that.emit('client', connection)
       })
     })
@@ -82,8 +82,8 @@ class MqttSecureServer extends tls.Server {
   }
 
   setupConnection (duplex) {
-    var that = this
-    var connection = new Connection(duplex, function () {
+    const that = this
+    const connection = new Connection(duplex, function () {
       that.emit('client', connection)
     })
   }
diff --git a/test/server_helpers_for_client_tests.js b/test/server_helpers_for_client_tests.js
index 9527d47e2..bc691d160 100644
--- a/test/server_helpers_for_client_tests.js
+++ b/test/server_helpers_for_client_tests.js
@@ -1,17 +1,17 @@
 'use strict'
 
-var MqttServer = require('./server').MqttServer
-var MqttSecureServer = require('./server').MqttSecureServer
-var debug = require('debug')('TEST:server_helpers')
+const MqttServer = require('./server').MqttServer
+const MqttSecureServer = require('./server').MqttSecureServer
+const debug = require('debug')('TEST:server_helpers')
 
-var path = require('path')
-var fs = require('fs')
-var KEY = path.join(__dirname, 'helpers', 'tls-key.pem')
-var CERT = path.join(__dirname, 'helpers', 'tls-cert.pem')
+const path = require('path')
+const fs = require('fs')
+const KEY = path.join(__dirname, 'helpers', 'tls-key.pem')
+const CERT = path.join(__dirname, 'helpers', 'tls-cert.pem')
 
-var http = require('http')
-var WebSocket = require('ws')
-var MQTTConnection = require('mqtt-connection')
+const http = require('http')
+const WebSocket = require('ws')
+const MQTTConnection = require('mqtt-connection')
 
 /**
  * This will build the client for the server to use during testing, and set up the
@@ -20,18 +20,18 @@ var MQTTConnection = require('mqtt-connection')
  * @param {Function} handler - event handler
  */
 function serverBuilder (protocol, handler) {
-  var defaultHandler = function (serverClient) {
+  const defaultHandler = function (serverClient) {
     serverClient.on('auth', function (packet) {
       if (serverClient.writable) return false
-      var rc = 'reasonCode'
-      var connack = {}
+      const rc = 'reasonCode'
+      const connack = {}
       connack[rc] = 0
       serverClient.connack(connack)
     })
     serverClient.on('connect', function (packet) {
       if (!serverClient.writable) return false
-      var rc = 'returnCode'
-      var connack = {}
+      let rc = 'returnCode'
+      const connack = {}
       if (serverClient.options && serverClient.options.protocolVersion === 5) {
         rc = 'reasonCode'
         if (packet.clientId === 'invalid') {
@@ -113,34 +113,36 @@ function serverBuilder (protocol, handler) {
     handler = defaultHandler
   }
 
-  switch (protocol) {
-    case 'mqtt':
-      return new MqttServer(handler)
-    case 'mqtts':
-      return new MqttSecureServer({
-        key: fs.readFileSync(KEY),
-        cert: fs.readFileSync(CERT)
-      },
-      handler)
-    case 'ws':
-      var attachWebsocketServer = function (server) {
-        var webSocketServer = new WebSocket.Server({server: server, perMessageDeflate: false})
-
-        webSocketServer.on('connection', function (ws) {
-          var stream = WebSocket.createWebSocketStream(ws)
-          var connection = new MQTTConnection(stream)
-          connection.protocol = ws.protocol
-          server.emit('client', connection)
-          stream.on('error', function () {})
-          connection.on('error', function () {})
-          connection.on('close', function () {})
-        })
-      }
+  if (
+    protocol === 'mqtt') {
+    return new MqttServer(handler)
+  } else if (
+    protocol === 'mqtts') {
+    return new MqttSecureServer({
+      key: fs.readFileSync(KEY),
+      cert: fs.readFileSync(CERT)
+    },
+    handler)
+  } else if (
+    protocol === 'ws') {
+    const attachWebsocketServer = function (server) {
+      const webSocketServer = new WebSocket.Server({ server: server, perMessageDeflate: false })
+
+      webSocketServer.on('connection', function (ws) {
+        const stream = WebSocket.createWebSocketStream(ws)
+        const connection = new MQTTConnection(stream)
+        connection.protocol = ws.protocol
+        server.emit('client', connection)
+        stream.on('error', function () {})
+        connection.on('error', function () {})
+        connection.on('close', function () {})
+      })
+    }
 
-      var httpServer = http.createServer()
-      attachWebsocketServer(httpServer)
-      httpServer.on('client', handler)
-      return httpServer
+    const httpServer = http.createServer()
+    attachWebsocketServer(httpServer)
+    httpServer.on('client', handler)
+    return httpServer
   }
 }
 
diff --git a/test/store.js b/test/store.js
index 1489b2138..f97fe72cc 100644
--- a/test/store.js
+++ b/test/store.js
@@ -1,7 +1,7 @@
 'use strict'
 
-var Store = require('../lib/store')
-var abstractTest = require('../test/abstract_store')
+const Store = require('../lib/store')
+const abstractTest = require('../test/abstract_store')
 
 describe('in-memory store', function () {
   abstractTest(function (done) {
diff --git a/test/unique_message_id_provider_client.js b/test/unique_message_id_provider_client.js
index 933d85b82..8853583c3 100644
--- a/test/unique_message_id_provider_client.js
+++ b/test/unique_message_id_provider_client.js
@@ -1,13 +1,13 @@
 'use strict'
 
-var abstractClientTests = require('./abstract_client')
-var serverBuilder = require('./server_helpers_for_client_tests').serverBuilder
-var UniqueMessageIdProvider = require('../lib/unique-message-id-provider')
-var ports = require('./helpers/port_list')
+const abstractClientTests = require('./abstract_client')
+const serverBuilder = require('./server_helpers_for_client_tests').serverBuilder
+const UniqueMessageIdProvider = require('../lib/unique-message-id-provider')
+const ports = require('./helpers/port_list')
 
 describe('UniqueMessageIdProviderMqttClient', function () {
-  var server = serverBuilder('mqtt')
-  var config = {protocol: 'mqtt', port: ports.PORTAND400, messageIdProvider: new UniqueMessageIdProvider()}
+  const server = serverBuilder('mqtt')
+  const config = { protocol: 'mqtt', port: ports.PORTAND400, messageIdProvider: new UniqueMessageIdProvider() }
   server.listen(ports.PORTAND400)
 
   after(function () {
diff --git a/test/util.js b/test/util.js
index 0dd559cb9..f0b8d0f9d 100644
--- a/test/util.js
+++ b/test/util.js
@@ -1,11 +1,11 @@
 'use strict'
 
-var Transform = require('readable-stream').Transform
+const Transform = require('readable-stream').Transform
 
 module.exports.testStream = function () {
   return new Transform({
     transform (buf, enc, cb) {
-      var that = this
+      const that = this
       setImmediate(function () {
         that.push(buf)
         cb()
diff --git a/test/websocket_client.js b/test/websocket_client.js
index a7f59897a..e91a76623 100644
--- a/test/websocket_client.js
+++ b/test/websocket_client.js
@@ -1,23 +1,23 @@
 'use strict'
 
-var http = require('http')
-var WebSocket = require('ws')
-var MQTTConnection = require('mqtt-connection')
-var abstractClientTests = require('./abstract_client')
-var ports = require('./helpers/port_list')
-var MqttServerNoWait = require('./server').MqttServerNoWait
-var mqtt = require('../')
-var xtend = require('xtend')
-var assert = require('assert')
-var port = 9999
-var httpServer = http.createServer()
+const http = require('http')
+const WebSocket = require('ws')
+const MQTTConnection = require('mqtt-connection')
+const abstractClientTests = require('./abstract_client')
+const ports = require('./helpers/port_list')
+const MqttServerNoWait = require('./server').MqttServerNoWait
+const mqtt = require('../')
+const xtend = require('xtend')
+const assert = require('assert')
+const port = 9999
+const httpServer = http.createServer()
 
 function attachWebsocketServer (httpServer) {
-  var webSocketServer = new WebSocket.Server({server: httpServer, perMessageDeflate: false})
+  const webSocketServer = new WebSocket.Server({ server: httpServer, perMessageDeflate: false })
 
   webSocketServer.on('connection', function (ws) {
-    var stream = WebSocket.createWebSocketStream(ws)
-    var connection = new MQTTConnection(stream)
+    const stream = WebSocket.createWebSocketStream(ws)
+    const connection = new MQTTConnection(stream)
     connection.protocol = ws.protocol
     httpServer.emit('client', connection)
     stream.on('error', function () {})
@@ -33,7 +33,7 @@ function attachClientEventHandlers (client) {
       client.connack({ returnCode: 2 })
     } else {
       httpServer.emit('connect', client)
-      client.connack({returnCode: 0})
+      client.connack({ returnCode: 0 })
     }
   })
 
@@ -87,7 +87,7 @@ attachWebsocketServer(httpServer)
 httpServer.on('client', attachClientEventHandlers).listen(port)
 
 describe('Websocket Client', function () {
-  var baseConfig = { protocol: 'ws', port: port }
+  const baseConfig = { protocol: 'ws', port: port }
 
   function makeOptions (custom) {
     // xtend returns a new object. Does not mutate arguments
@@ -104,11 +104,11 @@ describe('Websocket Client', function () {
   })
 
   it('should be able to transform the url (for e.g. to sign it)', function (done) {
-    var baseUrl = 'ws://localhost:9999/mqtt'
-    var sig = '?AUTH=token'
-    var expected = baseUrl + sig
-    var actual
-    var opts = makeOptions({
+    const baseUrl = 'ws://localhost:9999/mqtt'
+    const sig = '?AUTH=token'
+    const expected = baseUrl + sig
+    let actual
+    const opts = makeOptions({
       path: '/mqtt',
       transformWsUrl: function (url, opt, client) {
         assert.equal(url, baseUrl)
@@ -119,7 +119,8 @@ describe('Websocket Client', function () {
         url += sig
         actual = url
         return url
-      }})
+      }
+    })
     mqtt.connect(opts)
       .on('connect', function () {
         assert.equal(this.stream.url, expected)
@@ -133,7 +134,7 @@ describe('Websocket Client', function () {
       assert.strictEqual(client.protocol, 'mqttv3.1')
     })
 
-    var opts = makeOptions({
+    const opts = makeOptions({
       protocolId: 'MQIsdp',
       protocolVersion: 3
     })
@@ -145,20 +146,20 @@ describe('Websocket Client', function () {
 
   describe('reconnecting', () => {
     it('should reconnect to multiple host-ports-protocol combinations if servers is passed', function (done) {
-      var serverPort42Connected = false
-      var handler = function (serverClient) {
+      let serverPort42Connected = false
+      const handler = function (serverClient) {
         serverClient.on('connect', function (packet) {
-          serverClient.connack({returnCode: 0})
+          serverClient.connack({ returnCode: 0 })
         })
       }
       this.timeout(15000)
-      var actualURL41 = 'wss://localhost:9917/'
-      var actualURL42 = 'ws://localhost:9918/'
-      var serverPort41 = new MqttServerNoWait(handler).listen(ports.PORTAND41)
-      var serverPort42 = new MqttServerNoWait(handler).listen(ports.PORTAND42)
+      const actualURL41 = 'wss://localhost:9917/'
+      const actualURL42 = 'ws://localhost:9918/'
+      const serverPort41 = new MqttServerNoWait(handler).listen(ports.PORTAND41)
+      const serverPort42 = new MqttServerNoWait(handler).listen(ports.PORTAND42)
 
       serverPort42.on('listening', function () {
-        let client = mqtt.connect({
+        const client = mqtt.connect({
           protocol: 'wss',
           servers: [
             { port: ports.PORTAND42, host: 'localhost', protocol: 'ws' },