IIFE - Immediately Invoked Function Expression In JS

An IIFE, or Immediately Invoked Function Expression, is a function that is defined and immediately executed. It is a popular pattern in JavaScript that is often used to create a private scope for variables or to create a self-contained module.

To create an IIFE, you define a function using the function keyword, followed by a set of parentheses and a set of curly braces. You then immediately invoke the function by appending another set of parentheses after the closing curly brace.

Here's an example,

(function() {
    console.log('Hello, World!');
})();

Inside the IIFE, you can define variables and functions that are only accessible within the IIFE. This can be useful for creating private variables or for creating self-contained modules that can be imported and used in other parts of the application.

Here's an example of an IIFE that creates a self-contained module,

const myModule = (function() {
    // Private variables and functions
    let secret = 'This is a secret';

    function doSomething() {
        console.log('Doing something...');
    }
    // Public API
    return {
        sayHello: function() {
            console.log('Hello, World!');
        },
        doSomething: doSomething
    };
})();
// Use the module
myModule.sayHello(); // 'Hello, World!'
myModule.doSomething(); // 'Doing something...'
console.log(myModule.secret); // undefined (secret is a private variable)

In this example, the IIFE defines a secret variable and a doSomething function that are only accessible within the IIFE. It also defines a public API that consists of a sayHello function and the doSomething function.

The public API is returned from the IIFE and can be used by other parts of the application.