20. What is an IIFE (Immediately Invoked Function Expression)?

An IIFE (Immediately Invoked Function Expression) is a JavaScript function that runs as soon as it is defined. It is useful for creating a local scope and avoiding global variable pollution.

Syntax of an IIFE:

javascript
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(function() {
    console.log("This function runs immediately!");
})();

or using an arrow function:

javascript
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(() => {
    console.log("This also runs immediately!");
})();

Explanation:

• The function is wrapped in parentheses: (function() { ... })
• The () at the end invokes it immediately.
• It is often used to create a private scope and avoid polluting the global scope.

Use Cases:

1. Avoid Global Variable Pollution

   javascript
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   (function() {
       let message = "Hello, World!";
       console.log(message);
   })();
   // console.log(message); // Error: message is not defined
   

2. Encapsulation & Data Privacy

   javascript
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   let counter = (function() {
       let count = 0;
       return {
           increment: () => ++count,
           decrement: () => --count,
           getCount: () => count
       };
   })();
   
   console.log(counter.increment()); // 1
   console.log(counter.getCount());  // 1
   

3. Avoid Hoisting Issues in Loops

   javascript
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   for (var i = 0; i < 3; i++) {
       (function(index) {
           setTimeout(() => console.log(index), 1000);
       })(i);
   }
   // Output: 0, 1, 2 (instead of 3, 3, 3)
   

Key Takeaways:

• An IIFE is a self-executing function.
• It helps encapsulate variables and avoid conflicts.
• It is useful for creating module-like patterns in JavaScript.

Would you like a more detailed example for a specific use case? 🚀