Function Declaration

Last Updated: 21st October 2025

There are different way to declare a function in JavaScript.Every Function can have a name, parameters, and a body.

  • functionName → Name of the function
  • parameters → Optional values you can pass into the function
  • Code inside → Runs when the function is called

Here we see some of them without parameters.

Function Declaration

  • Function Declaration is a named function that is defined using the function keyword.
  • It is hoisted, which means it can be called before it is defined in the code.

Hinglish Tip 🗣: Function Declaration ka matlab hai “pehle function define karo aur fir kahin bhi call kar sakte ho”.

function functionName() {
  // function body
}

Example:

function greet() {
  console.log("Hello, world!");
}

greet(); // Output: "Hello, world!"

Function Expression or Anonymous Function

  • A function expression is a function stored in a variable.
  • Unlike function declaration, it is not hoisted → you cannot call it before definition.
  • Can be named or anonymous.

Hinglish Tip 🗣: Function Expression = “Function ko variable me store karna”. Call tabhi ho sakta hai jab variable define ho chuka ho.

// Anonymous function expression
const functionName = function (parameters) {
  // code block
};

// Named function expression
const functionName = function actualName(parameters) {
  // code block
};

Example:

const greet = function () {
  console.log("Hello, world!");
};

greet(); // Output: "Hello, world!"

Arrow Function

  • Arrow Functions are a shorter syntax to write functions in JavaScript.
  • Introduced in ES6 (ECMAScript 2015).
  • They are anonymous (no name) and often used as callback functions or inside array methods like map(), filter(), forEach(), etc.

Hinglish Tip 🗣: Arrow function ek chhota shortcut hai — likhne me easy aur modern JavaScript me bahut use hota hai.

const functionName = () => {
  // code block
};

Example:

const greet = () => {
  console.log("Hello, world!");
};

greet(); // Output: "Hello, world!"

💡 Quick Practice

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