feat(jira-default-wl-type): be more careful with setting default wlType

Also introduce more meaningful code ordering, plus some more cleanup.

JIRA_def-worklog-type.user.js

@@ -3,12 +3,12 @@
 // @namespace   pbo
 // @description Changes default Worklog Type in JIRA with the Worklog express add-on.
 // @match       https://your.jira.example.com/browse/*
-// @version     1.1.0
+// @version     1.1.1
 // @grant       GM_registerMenuCommand
 // @require     https://ajax.googleapis.com/ajax/libs/jquery/1.12.4/jquery.min.js
 // ==/UserScript==
 
-(function($) {
+(function ($) {
 
 /* Great users of this script can safely change values of the following constants: */
 
@@ -19,8 +19,10 @@
  * 2. Find the <select> element with id "wl-type" in your browser's HTML inspector.
  * 3. Inside that element, find the <option> element which you prefer as the default choice.
  * 4. Copy the "value" attribute of that element here.
+ *
+ * Defaults to null.
  */
-var DEFAULT_WORKLOG_TYPE = 1;
+var DEFAULT_WORKLOG_TYPE = null;
 
 /**
  * Whether to remember which type was lastly selected for a given issue
@@ -63,26 +65,45 @@ try {
 var PROCESSED_FLAG = 'def-wltype-processed';
 
 function setDefaultWorklogType() {
-  var targets = $('#wl-type').filter(':not([' + PROCESSED_FLAG + '])');
-
+  var targets = $('#wl-type').filter(`:not([${PROCESSED_FLAG}])`);
+
+  // note: there should be always 1 item (select field)
   for (var i = 0; i < targets.length; i++) {
-    // note: there should be always 1 item (select field)
-    var wlType = REUSE_ISSUE_LAST_WORKLOG_TYPE ? getIssueWorklogType() : DEFAULT_WORKLOG_TYPE;
-    trace('Setting default worklog type ' + wlType + ' to item #' + (i + 1));
     var target = targets[i];
     $(target).attr(PROCESSED_FLAG, true);
 
     if (REUSE_ISSUE_LAST_WORKLOG_TYPE) {
-      unsafeWindow.$(target).on("change", storeIssueWorklogType);
+      unsafeWindow.$(target).on('change', storeIssueWorklogType);
+    }
+
+    var wlType = REUSE_ISSUE_LAST_WORKLOG_TYPE ? getIssueWorklogType() : DEFAULT_WORKLOG_TYPE;
+
+    // sanity checks
+    if ($(target).val() == wlType) {
+      trace('Default worklog type does not differ from actual value - do nothing');
+      continue;
+    }
+    if (!wlType && !DEFAULT_WORKLOG_TYPE) {
+      trace('No predefined nor remembered default worklog type - do nothing');
+      continue;
+    }
+    if ($(target).children().toArray().every(option => $(option).val() != wlType)) { // eslint-disable-line no-loop-func
+      console.warn(`DEFAULT_WORKLOG_TYPE and/or remembered value of [${wlType}] is not present among possible options - do nothing`);
+      continue;
     }
 
+    trace(`Setting default worklog type ${wlType} to item #${i + 1}`);
     $(target).val(wlType);
     // note: if we call trigger() on this script's jQuery, page's jQuery won't catch the event
     unsafeWindow.$(target).trigger('change');
   }
 }
 
-setInterval(setDefaultWorklogType, 500);
+if (!DEFAULT_WORKLOG_TYPE && !REUSE_ISSUE_LAST_WORKLOG_TYPE) {
+  trace('None of the script options are enabled - do nothing');
+} else {
+  setInterval(setDefaultWorklogType, 500);
+}
 
 trace('started');
 
@@ -93,7 +114,7 @@ function getIssueWorklogType() {
 
   var wlType = window.localStorage.getItem(WL_TYPE_KEY_PREFIX + issueKey);
   if (wlType) {
-    trace('Using worklog type for issue from local storage: ' + wlType);
+    trace(`Using worklog type for issue from local storage: ${wlType}`);
   } else {
     wlType = DEFAULT_WORKLOG_TYPE;
   }
@@ -105,7 +126,7 @@ function storeIssueWorklogType(event) {
   var issueKey = $('#key-val').text();
 
   var wlType = $(event.target).val();
-  trace('Storing worklog type for issue in local storage: ' + wlType);
+  trace(`Storing worklog type for issue in local storage: ${wlType}`);
   window.localStorage.setItem(WL_TYPE_KEY_PREFIX + issueKey, wlType);
 }