20-function.md

==========Functions==========

funcrion vah code hota hain.jise hum bar bar reuse kar skte hain.function ki help sa bhut bada bada cose ko chote chote parts ma devide kar deya jata hain.

• javascript ma function 3 type sa bana skte hain. 1.function declaration. 2.function expression. 3.arrow function

What is function declaration:

function decleratio me function ka name dana jaruri hain.function decleration ko jis line par declar kiya hai.us line sa phala call kar skte hain. function decleration ki hoisting hoti hain.

• function declaration syntex:

function sum(a, b) {
return a + b;
}
var ans = sum(10, 20);

Parametar vah variables hota hain. jinhe hum function me brackets ka andr likte hain. parametar ka kuch bhi nam ho skta hain.ak function yadi kuch bhi return nhai kar raha hain.to undifine return hoga.oterwise jo value return ki hain voh value return hogi.

Argument or paremetar ki mapping left to right hoti hain.yadi kisi parametar ki value pass nahi kb hain. to us parametar ki value undifine hogi.function ki return value ko hum kisi variable ma store krva skte hain.

What is function expression:

function expression bhi function decleration ki trha hota hota hain.lakin in dono me kuch defrance hain.jase ki function expression ka name nahi hota hain.is leye is ko variable ma store keya jata hain.function expression ko jis line par banaya gaya hain.us line sa phala use nahi kar skte hain. functio expression ki hoisting nahi hoti hain.

• function expression syntex:

var sum = function (a, b) {
return a, b;
};
var ans = sum(10, 20);
console.log(ans);

What is arrow function:

arro function me function keyword ka use nahi hota hota. yadi arrow function me single line ka code hain.vah us code ma hum kuch return kar rahe hain to crlibresh vah return likhne ki jaruri nahi hain.arrow function otomatic khud return karega.yadi arrow function ma hum kuch bhi return nahi kar rahe hain. and code ak line se jyada hain.to crliresh lagna jaruri hain.arrow function ko bhi hum phala call nahi kar skte hain.arrow function ki bhi hoisting nhai hoti hain.

• arrow function syntex:

let test = () => expression;
var sum = (a, b) => {
return a + b;
};
console.log(sum(20, 10));

Anonymous function vah function jiska koi name nahi hota.us ko anonymous function khate hain.

• syntex :

let test = function(param1, param2)
{
//write your logic here
}

let ex_var = "A Variable";
let test = function () {
document.write(`Full Name : ${arguments[0]} <br>`);
document.write(`External Variable : ${ex_var}`);
};
test("Rahul Rajput");

• function inside function (function ka andr function)

What is function inside function:

Yadi koi function kisi dusrye function ke andr bnaya gaya hai. to us function ko sirf bhar vale function ke andr he use keya jo skta hain.andr vale function ko hum bhar se call nahi kar skte hain.

• for example

function sum(a, b) {
console.log(a + b);
hello();
function hello() {
console.log("hello");
}
}
sum(10, 20);

• Arguments object function ko pass keya gaya arguments ko btata hain.

function sum(a, b, c) {
console.log(arguments);
}
sum(1, 2, 3, 4, 5);