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

PreviousJava ScriptNextExpress js

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