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Function Kya Hai ?

Function ek predefined block of code hota hai jo specific task perform karta hai. Yeh ek reusable component hai jo bar-bar likhne ki zaroorat nahi hoti. Function input le sakta hai (parameters) aur output de sakta hai (return value). Har function ka ek unique naam hota hai jo usko identify karta hai.

Programming languages jaise C, C++, Java, Python me functions ka use hota hai code modular aur efficient banane ke liye. Function do types ke hote hain:

• Built-in functions: Jo language me predefined hote hain.
• User-defined functions: Jo programmer khud banata hai.

Agar simple shabdon mein samjhein toh function ek machine ki tarah hota hai jo input leta hai, usko process karta hai aur output deta hai.

Types of Functions in JavaScript

JavaScript mein multiple tarike ke functions hote hain:

• Function Declaration (Named Function)
• Function Expression
• Arrow Function (ES6)
• Anonymous Function
• Immediately Invoked Function Expression (IIFE)
• Higher-Order Function
• Callback Function

Ab in sabko detail mein samajhte hain ek-ek karke.

1. Function Declaration (Named Function)

Function Declaration (Named Function) ek aisa method hai jisme ek function ko ek unique naam diya jata hai aur usse code me kahi bhi call kiya ja sakta hai. Ye functions “function” keyword ke sath start hote hain, followed by function name aur parentheses (). Iske andar function ka logic ya instructions define ki jati hain. Function declarations hoisting support karte hain, yani inhe define karne se pehle bhi call kiya ja sakta hai. Ye reusable hote hain, jisse code modular aur maintainable banta hai.

Example:

function greet() {
    console.log("Hello, Welcome to JavaScript!");
}
greet(); // Output: Hello, Welcome to JavaScript!

Explanation:

• function keyword ka use karke function greet() define kiya.
• console.log() ka use karke ek message print kiya.
• Function call greet(); likhne se function execute hua.

2. Function Expression

Function Expression ek JavaScript me ek tarika hai jisme function ko ek variable ya constant me assign kiya jata hai. Isme function ka naam optional hota hai, aur ise anonymous function bhi kaha jata hai agar koi naam na diya ho. Function Expression ko execution ke dauraan define kiya jata hai, is wajah se yeh hoisting ka part nahi hota. Ise callback functions aur closures ke liye bhi use kiya jata hai. Ek baar assign hone ke baad, ise variable ki tarah treat kiya jata hai aur kisi bhi operation me istemal kiya ja sakta hai jaise ki arguments pass karna ya return karna.

Example:

const sum = function(a, b) {
    return a + b;
};
console.log(sum(5, 3)); // Output: 8

Explanation:

• sum ek variable hai jisme ek function store hai.
• Function ke andar a aur b parameters hain.
• return keyword se result wapas bheja.
• Function ko console.log(sum(5, 3)); likh ke call kiya.

3. Arrow Function (ES6)

Arrow function (ES6) ek concise aur modern syntax hai jo JavaScript mein functions likhne ke liye use hoti hai. Yeh function => (arrow) ka use karta hai, jo traditional function expressions ki tarah kaam karta hai, par iska syntax short aur readable hota hai. Arrow functions automatically this ka reference lexical scope se lete hain, jo ki methods aur callbacks likhne mein helpful hota hai. Agar function ka sirf ek expression ho, to {} aur return likhne ki zaroorat nahi hoti. Yeh mainly callback functions aur array methods jaise map(), filter(), reduce() mein commonly use hota hai.

Example:

const multiply = (a, b) => a * b;
console.log(multiply(4, 5)); // Output: 20

Explanation:

• Arrow function ka syntax short hota hai.
• Agar ek hi line ka function ho, toh {} aur return likhne ki zaroorat nahi.

4. Anonymous Function

An Anonymous Function ek aisi function hoti hai jiska koi specific naam nahi hota. Ye mostly temporary tasks ke liye use hoti hai jaha ek baar execute karne ke baad uska reference zaroori nahi hota. JavaScript me ise arrow function ya lambda function bhi kaha jata hai. Ye higher-order functions ke sath commonly use hoti hai, jaise map(), filter(), reduce(). Iska syntax concise hota hai aur ye callback functions ke liye bhi kaafi useful hoti hai. Anonymous functions dynamically create ki jati hain aur memory efficiency badhane me madad karti hain, kyunki ye bina koi extra reference store ki execute hoti hain.

Example:

setTimeout(function() {
    console.log("This will run after 3 seconds");
}, 3000);

Explanation:

• Yeh function setTimeout() mein likha gaya hai bina kisi naam ke.
• 3000 milliseconds (3 sec) ke baad execute hoga.

5. Immediately Invoked Function Expression (IIFE)

Immediately Invoked Function Expression (IIFE) ek aisa JavaScript function hai jo turant execute ho jata hai jaise hi define hota hai. Yeh function ek enclosed scope create karta hai jo variables ko global scope se alag rakhta hai, jisse naming conflicts avoid hote hain. IIFE ko parentheses () ke andar wrap karke likha jata hai aur last me () lagakar invoke kiya jata hai. Iska use commonly encapsulation, asynchronous operations, aur modular programming ke liye hota hai. Yeh approach performance aur security improve karti hai, kyunki yeh unwanted global variable pollution ko prevent karti hai.

Example:

(function() {
    console.log("IIFE function executed!");
})();

Explanation:

• Function ko parentheses () ke andar wrap kiya.
• Last mein ek () likhne se function turant execute ho gaya.

6. Higher-Order Function

Higher-Order Function ek aisa function hota hai jo ya to ek ya ek se zyada functions ko as argument accept karta hai ya ek function ko return karta hai. Ye functional programming ka ek important concept hai jo code ko modular aur reusable banata hai. JavaScript jaise languages me map(), filter(), aur reduce() higher-order functions ke examples hain. Ye functions dusre functions ko manipulate karne ki ability dete hain, jisse code concise aur readable hota hai. Higher-order functions functional programming paradigms ka core part hote hain jo abstraction aur flexibility badhane me madad karte hain.

Example:

function operate(a, b, operation) {
    return operation(a, b);
}
const addition = (x, y) => x + y;
console.log(operate(10, 5, addition)); // Output: 15

Explanation:

• operate() ek higher-order function hai jo ek function (operation) accept karta hai.
• addition() function ko pass kiya gaya aur ye numbers add kar raha hai.

7. Callback Function

Callback function ek aisa function hota hai jo kisi doosre function ko argument ke roop me diya jata hai aur bad me execute hoti hai. Yeh asynchronous programming me kaafi upyogi hoti hai, jisme ek function doosre function ke complete hone ka intezar kiye bina execute ho sakta hai. JavaScript me callback functions event handling, API requests aur asynchronous operations me use hoti hain. Yeh ek higher-order function ka concept hai, jisme ek function doosre function ko control karta hai. Callback functions synchronous ya asynchronous ho sakti hain, jisme asynchronous callbacks time-consuming tasks ko efficiently handle karne me madad karti hain.

Example:

function fetchData(callback) {
    console.log("Fetching data...");
    callback();
}
fetchData(function() {
    console.log("Data fetched successfully!");
});

Explanation:

• fetchData() function ek callback function leta hai.
• Function complete hone ke baad callback function execute hota hai.

Function with Default Parameters

Agar kisi function ko koi parameter pass nahi kiya jaye, toh default value assign karne ka option hota hai.

Example:

function greet(name = "Guest") {
    console.log(`Hello, ${name}!`);
}
greet(); // Output: Hello, Guest!
greet("Sandeep"); // Output: Hello, Sandeep!

Explanation:

• Agar function call karte waqt argument pass nahi hota toh name = “Guest” use hota hai.

Function Scope and Hoisting

Scope:

• Global Scope: Function har jagah accessible hota hai.
• Local Scope: Function ke andar declare kiye variables sirf us function ke andar access hote hain.

Example:

function testScope() {
    let message = "Hello";
    console.log(message);
}
console.log(message); // Error: message is not defined

Explanation:

• message variable sirf testScope() function ke andar accessible hai.

Hoisting

Function declarations fully hoisted hote hain, yani inhe define karne se pehle bhi call kiya ja sakta hai.

Example:

hoistedFunction(); // Output: Hoisted function called!
function hoistedFunction() {
    console.log("Hoisted function called!");
}

Explanation:

• Function ko define karne se pehle hi call kar sakte hain kyunki JavaScript isko memory mein rakhta hai.

JavaScript functions bahut powerful hote hain aur code ko modular, reusable aur maintainable banate hain. Aapko function declaration, expression, arrow functions, IIFE, higher-order functions, callbacks aur scope ka concept clear hona chahiye.

Quiz: Test Your Knowledge on JavaScript Functions

Bonus: Practical Application!

Aaj hi apne webpage par JavaScript functions ka istemal karke dekhein!

JavaScript functions ko sahi tareeke se samajhne ke liye different types jaise function declaration, function expression, arrow functions, IIFE (Immediately Invoked Function Expressions), callbacks, aur higher-order functions ka upayog karein aur apne JavaScript code ko aur bhi efficient banayein.