Immediately Invoked Function Expressions (IIFE) in JavaScript

Immediately Invoked Function Expressions (IIFE) are JavaScript functions that are executed immediately after they are defined. They are typically used to create a local scope for variables to prevent them from polluting the global scope.

Syntax:

(function (){ 
// Function Logic Here. 
})();

Immediately Invoked Function Expressions (IIFE) Examples

Example: Here’s a basic example of an IIFE .

Javascript

(function() {
    // IIFE code block
    var localVar = 'This is a local variable';
    console.log(localVar); // Output: This is a local variable
})();

Output

This is a local variable

Explanation: The function is wrapped in parentheses (function() { ... }), followed by () to immediately invoke it.

Example 2: Here’s another example of an IIFE that stores and display result.

Javascript

var result = (function() {
    var x = 10;
    var y = 20;
    return x + y;
})();

console.log(result); // Output: 30

Output

30

Explanation: The IIFE is immediately invoked and returns the sum of x and y. The result of the IIFE, which is 30, is assigned to the variable result.

IIFEs are commonly used to create private scope in JavaScript, allowing variables and functions to be encapsulated and inaccessible from outside the function.

Example: Here’s an example demonstrating how an IIFE can be used to create private variables:

Javascript

var counter = (function() {
    var count = 0;

    return {
        increment: function() {
            count++;
        },
        decrement: function() {
            count--;
        },
        getCount: function() {
            return count;
        }
    };
})();

// Increment the counter
counter.increment();
counter.increment();
counter.increment();

console.log(counter.getCount()); // Output: 3

// Trying to access the private count variable directly
console.log(counter.count); // Output: undefined (cannot access private variable)

Output

3
undefined

Explanation: Here, count is a private variable scoped to the IIFE, inaccessible from outside. The returned object exposes methods (increment, decrement, and getCount) that allow controlled manipulation and access to the private count variable.

Use Cases Of IIFE

• Avoid polluting the global namespace.
• To create closures in JavaScript.
• IIFE is used to create private and  public variables and methods.
• It is used to execute the async and await function.
• It is used to work with require function.