nodejs-snippets

Node.js snippets

Useful info

Installing dependencies

If a project has a package.json file, by running it will install everything the project needs, in the node_modules folder, creating it if it's not existing already:

npm install

You can also install a specific package by running

npm install <package-name>

Often you'll see more flags added to this command:

• --save-dev installs and adds the entry to the package.json file devDependencies
• --no-save installs but does not add the entry to the package.json file dependencies
• --save-optional installs and adds the entry to the package.json file optionalDependencies
• --no-optional will prevent optional dependencies from being installed

The difference between devDependencies and dependencies is that the former contains development tools, like a testing library, while the latter is bundled with the app in production.

Running tasks

npm run <task-name>

Installation location

The npm root -g command will tell you where that exact location is on your machine.

Use or execute a package installed using npm

To use it in your code, you just need to import it into your program using require:

const express = require('express')

If the package is an executable:

npm install cowsay
npx cowsay take me out of here

About package.json

• More info @ https://nodejs.dev/learn/the-package-json-guide
• More info @ https://nodejs.dev/learn/the-package-lock-json-file
• More info @ https://nodejs.dev/learn/uninstalling-npm-packages

Find the installed version of an npm package

npm list 
npm list -g // for globally installed packages
npm view [package_name] version // to see the latest available version of the package on the npm repository

npm global or local packages?

• In your code you can only require local packages
• In general, all packages should be installed locally.
• Updating a global package would make all your projects use the new release, and as you can imagine this might cause nightmares in terms of maintenance, as some packages might break compatibility with further dependencies, and so on.
• A package should be installed globally when it provides an executable command that you run from the shell (CLI), and it's reused across projects.

npm dependencies and devDependencies

When you add the -D flag, or --save-dev, you are installing it as a development dependency, which adds it to the devDependencies list.

Development dependencies are intended as development-only packages, that are unneeded in production. For example testing packages, webpack or Babel.

When you go in production, if you type npm install and the folder contains a package.json file, they are installed, as npm assumes this is a development deploy.

You need to set the --production flag (npm install --production) to avoid installing those development dependencies.

The npx Node.js Package Runner

• npx lets you run code built with Node.js and published through the npm registry.
• Examples:
  • running the vue CLI tool to create new applications and run them: npx @vue/cli create my-vue-app
  • creating a new React app using create-react-app: npx create-react-app my-react-app

The Node.js http module

More info @ https://nodejs.dev/learn/the-nodejs-http-module

It can be included using

const http = require('http')

• Methods

  • http.createServer(): returns a new instance of the http.Server class.
  • http.request(): makes an HTTP request to a server, creating an instance of the http.ClientRequest class.
  • http.get(): similar to http.request(), but automatically sets the HTTP method to GET, and calls req.end() automatically.

• The HTTP module provides 5 classes:

  • http.Agent
  • http.ClientRequest
  • http.Server
  • http.ServerResponse
  • http.IncomingMessage

Node.js Buffers

More info @ https://nodejs.dev/learn/nodejs-buffers

A buffer is an area of memory. Most JavaScript developers are much less familiar with this concept, compared to programmers using a system programming languages (like C, C++, or Go), which interact directly with memory every day.

To create a buffer:

const buf = Buffer.from('Hey!')
const buf = Buffer.alloc(1024)

To access the content:

const buf = Buffer.from('Hey!')
console.log(buf[0]) //72
console.log(buf[1]) //101
console.log(buf[2]) //121

You can print the full content of the buffer using the toString() method:

console.log(buf.toString())

To copy a buffer:

const buf = Buffer.from('Hey!')
const bufcopy = Buffer.alloc(4) //allocate 4 bytes
bufcopy.set(buf)

Node.js Streams

More info @ https://nodejs.dev/learn/nodejs-streams

They are a way to handle reading/writing files, network communications, or any kind of end-to-end information exchange in an efficient way.

The Node.js stream module provides the foundation upon which all streaming APIs are built. All streams are instances of EventEmitter

Development vs production

More info @ https://nodejs.dev/learn/nodejs-the-difference-between-development-and-production

Node.js assumes it's always running in a development environment. You can signal Node.js that you are running in production by setting the NODE_ENV=production environment variable.

Node.js with WebAssembly

More info @ https://nodejs.dev/learn/nodejs-with-webassembly