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What is IIFE (immediately invoked Function expression) in JavaScript

IIFE (Immediately Invoked Function Expression) is an immediately invoked function expression in JavaScript. It's a function that is defined and immediately called as soon as the interpreter reaches it.

Syntax

javascript
(function () { // code inside IIFE })();

Or using arrow function:

javascript
(() => { // code inside IIFE })();

Why Use IIFE?

  • Isolates variables and functions from outer scope.
  • Used to create local scope, especially before let and const appeared.
  • Often used in modular development when you need to hide internal implementation details.

Usage Example

javascript
(function () { const message = "Hello from IIFE!"; console.log(message); // "Hello from IIFE!" })(); console.log(message); // ReferenceError: message is not defined

Variable message is only available inside IIFE and inaccessible outside — this avoids polluting global scope.

IIFE with Arguments

javascript
(function (name) { console.log(`Hello, ${name}!`); })("Alice"); // Hello, Alice!

When is it Used?

  • For one-time data initialization (e.g., setup)
  • For creating private variables and closures
  • In old pre-ES6 projects for module simulation

Example: counter with closure via IIFE

javascript
const counter = (function () { let count = 0; return function () { count++; console.log(count); }; })(); counter(); // 1 counter(); // 2

Summary

IIFE is a function that is immediately called after definition.

  • Used for code isolation and creating private namespace.
  • It's a useful technique for writing modular and safe code.

Fact:

IIFE is one of the simplest ways to organize privacy in JavaScript without classes and modules.

Short Answer

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