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IIFE

IIFE (Immediately Invoked Function Expression)

Introduction

An IIFE is a function that runs immediately after being defined. It creates a new scope for variables, preventing them from leaking into the global scope.

Syntax

(function() {
  // code runs immediately
})();

// Arrow function variant
(() => {
  // code runs immediately
})();

Why Do We Need This?

Before ES6 modules, IIFEs were the primary way to create private scopes and avoid polluting the global namespace.

Visual Explanation

flowchart LR
    A["Function Definition"] --> B["Immediately Invoked"]
    B --> C["New Scope Created"]
    C --> D["Variables Are Private"]
    D --> E["Global Scope Not Polluted"]

Examples

// Private scope
(function() {
  const privateVar = 'secret';
  console.log(privateVar); // 'secret'
})();

console.log(privateVar); // ReferenceError

// Module pattern (pre-ES6)
const module = (function() {
  const private = 'private data';
  return {
    getPrivate: () => private
  };
})();

console.log(module.getPrivate()); // 'private data'

Summary

IIFE runs immediately after definition
Creates a private scope
Was essential for module pattern before ES6
Still useful for isolated code execution

Further Reading

MDN: IIFE