Java Script in my Understanding

1) How to Declare the variables in JS ?

We use var, let, const keyword before declaring a variable.

Avoid using var because of issue in block scope and functional scope.

JS is kind enough to declare variable without keywords but it's not a best practice.

const name = 'pramod';
let age = 19;
var email = 'pramodambati1@gmail.com';
city = hyderabad
let state; // undefined

2) what all the datatypes in JS?

There are two type of datatypes in JS.

1) Primitive Data types

2) Non-Primitive (Reference) Data types

Primitive Data types

const name = 'pramod'; // String
let age = 22; // Number
let isLoggedIn = false; // Boolean
let state; // Undefined
let temperature = null; // null (Representation of empty value)
let bigNumber = 10494917943941985n; // Big Int
let isSym = Symbol('test'); // Symbol
const id = Symbol('123')
const anotherId = Symbol('123') // Generate Unique Symbol.

console.log(id === anotherId) // false

// Strict Check === checks datatype not only its value

console.log(2 == '2'); // true
console.log(2 === '2'); // false

2) Reference Datatype

Reference is directly allocated to the memory.

// Array, Object, Function

const heros = ['IronMan', 'BatMan', 'SuperMan'] 

const myObj = {
    name = 'pramod',
    age = 22
}

const myFunction = funtion() {
    return 'Hello World';
}

3) Return Type of Datatypes in JS.

/*
Return type of Datatypes in JavaScript
1) Primitive Datatypes
       Number => number
       String  => string
       Boolean  => boolean
       null  => object
       undefined  =>  undefined
       Symbol  =>  symbol
       BigInt  =>  bigint

2) Non-primitive Datatypes
       Arrays  =>  object
       Function  =>  function  // we call it as object function
       Object  =>  object

       https://262.ecma-international.org/5.1/#sec-11.4.3
*/

3) Primitive and Refernce In JS?

let firstName = 'pramod'
let anotherName = firstName
another name = 'James'

console.log(firstName) // 'pramod'
console.log(anotherName) // 'James'

let userOne = {
    email: "pramod@gmail.com",
    upiId: "9390095818"
}

let userTwo = userOne

userTwo.email = 'pramodambati1@gmail.com'
console.log(userOne.email) // pramodambati1@gmail.com
console.log(userTwo.email) // pramodambati1@gmail.com

// Primitive values goes into stack and whenever you take something inside the stack, you get only a copy of it.

// Where as in Heap you w/ill get reference change you make or update , you do it in the original value only.

Credits: Chai Aur Code JS Playlist.