NODE JS

	/*
	Nodejs is javascript engine from Chrome V8 Engine .
	Which runs javascript code in the backend
	node js is non blocking io module ie., if any lines takes more time , than the cpu does not block other lines and continues execution of other lines
	npm - package manager for js .Similar to pip in python
	Note: Never push node module dependencies to Git as it is huge
	docs: all functions in npm is
	- https://nodejs.org/dist/latest-v17.x/docs/api/
	- https://nodejs.dev/learn/introduction-to-nodejs
	*/
	//ubuntu Linux Install
	sudo apt update
	sudo apt install nodejs
	node -v // --version
	sudo apt install npm
	//Run Node
	node file.js //execute file
	node //start nodejs shell
	//package create and install
	npm init //create a project using npm
	npm install express --save
	npm install -g package_name //install globally
	5 //5
	5+5 //10
	console.log("hi") //print
	console.log(__filename) //
	//variable
	var a=1
	const c =1
	//Map
	const map1 = new Map();
	map1.set('a', 1);
	console.log(map1.get("a"))
	//List
	var a = [1, "two", "three", 4];
	if (a[0] == 1)
	console.log("equal")
	else
	console.log("not")
	//Loop
	for (i = 0; i <= a.length - 1; i++) console.log(i)
	a.forEach(i => console.log(i))
	//function
	function f(name){console.log(name)} //f("hi")
	//IMPORT OTHER FILE
	//library.js
	d = { "name": "deepak", "age": 100 }
	module.exports = { add, d}
	function add(x, y) { return x + y;}
	//index.js
	const lib = require("./library.js")
	console.log(lib.add(4, 2), lib.d);
	//common js vs ESM
	const library = require("library") //commonjs
	import * from library as lib //ESM - only work when you convert the current project to module ( "type": "module")
	//IMPORT DEPENDENCY
	const dep = require("os")
	console.log(os.freemem())
	//SYNC VS ASYN LIBRARIES
	const fs = require("fs")
	fs.writeFileSync("f.txt","data to be written")
	fs.writeFile("f.txt","data to be written", () =>{console.log("done writing")}) // intimate user once data is written
	//IMPORTATN LIBRARIES
	path //folder path
	fs //file
	url
	events
	express //to create server alternate to "http" package
	//EVENTS
	const event = require('events');
	class E extends event {}
	const e = new E();
	e.on('WaterFull', () => {
	console.log('Please turn off the motor!');
	setTimeout(() => {
	console.log('Please turn off the motor! Its a gentle reminder');
	}, 3000);
	});
	console.log("started")
	e.emit('WaterFull'); //start event when you receive "Waterfull"
	console.log("The script is still running")
	// Result
	started
	Please turn off the motor!
	The script is still running
	Please turn off the motor! Its a gentle reminder
	//EXPRESS - https://expressjs.com/en/starter/hello-world.html
	const express = require('express')
	const path = require('path')
	const app = express()
	const port = 3000
	//http://localhost:3000/home/hi?id=5
	app.get('/home/:param', (req, res) => {
	res.send('Hello World!' + req.params.param + req.query.id)
	})
	app.get('/file', (req, res) => {
	res.sendFile(path.join(__dirname, "file.html"))
	})
	app.post('/file', function(req, res) {
	res.send(("Working"));
	// console.log('req.body.name', req.body['submit']);
	});
	app.get('/json', (req, res) => {
	res.json({ "name": "deepak" })
	})
	app.listen(port, () => {
	console.log(`Example app listening at http://localhost:${port}`)
	})

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