Node js

What is Nodejs?

• Environment to run javascript out of browser

• Built on top of chrome's V8 JS Engine (fastest and most efficient as of now)

• Full-stack and big community

Familiarity required for understaing?

• HTML, CSS, JS, ES6

• Callbacks, Promises, Async-Await

Nodejs

Properties

• No DOM

• No Window

• Server Side Apps (pure logic without UI or graphics)

• File System

• Versions (no browser dependence)

• CommonJS

Global - (No Window in here)

• __dirname - path to current directory

• __filename - file name

• require - function to use modules (NodeJS)

• module - info about current module (file)

• process - info about env where the program is being executed

• console -

• setTimeout and setInterval

Modules in node

• Create multiple modules to keep the app clean and seggregated

• module.exports

• Built-in modules

  • OS (for interaction with OS and server) - require('os')

    • os.userInfo()

    • os.uptime()

    • os.type()

    • os.totalmem()

    • os.freemem()

  • PATH - require('path')

    • path.join(a1, a2, a3)

    • path.basename("some path")

    • path.resolve(a1,a2,a3)

  • FS - require('fs')

    • fs.readFileSync("file path", encoding)

    • fs.writeFileSync("file path", "content to write")

      • if file is not there, create one

      • if file is already there, will overwrite

      • for appending, path one more argument: {flag: 'a'}

    • readFile and writeFile are also possible, with callback functions

  • HTTP - require('http')

    • http.createServer((req, res) => {})

NPM (Node Package Manager)

• what is it?

• Commands:

  • npm --version

  • npm i <package name> (i to install a node package, locally installed)

  • (sudo)? npm i -g <package name> (to install package globally, use in any project)

  • npm i -D <package name> (-D add package to devDependencies in package.json file)

  • npm i --save <package name> (--save add package to dependencies in package.json file)

• package.json - menifest file, stores important information about the project/package

  • npm init -y (to create package.json, y flag set everything by default)

Important Topics

• Event Loop

  • Allows node js to perform non-blocking I/O operations (despite JS being single-threaded)

  • It does so by offloading operations to system kernel whenever required

  • References:

    • a

• Async Patterns

  • a

• Events Emitter

  • s

• Streams

HTTP Requests and Response Cycle

How web works and data transfer on web?

• User / client sends http request, server sends http response

• http messages have following parts:

  • start line

  • optional header (meta information, key value pairs)

  • optional body

  • blank line (to indicate end of data packate)

• Request methode part:

  • method

    • get

    • post

    • delete

    • update

    • create

  • url

  • http version

• Response methode part:

  • status code

  • status text

  • headers

  • body (optional)

References

• https://www.w3schools.com/nodejs/
• https://www.tutorialspoint.com/nodejs/index.htm
• https://nodejs.dev/en/learn/introduction-to-nodejs
• https://www.javatpoint.com/nodejs-tutorial