How to Define Function Within Another Function in JavaScript?

In JavaScript, the concept of creating a function inside another function is known as nesting or creating an inner function. In the provided example, `innerFunction` is nested within `outerFunction`, allowing it to access both its own local scope and the scope of the outer function. Importantly, the inner function is confined to the scope of the outer function and cannot be accessed from outside `outerFunction`. This nested structure is frequently employed for encapsulating functionality, forming what is known as a closure in JavaScript. It's a powerful technique for creating modular and private code within specific scopes.

In JavaScript, you can define a function inside another function. This is often referred to as creating a "nested" or "inner" function. Here's a simple example:

javascript
function outerFunction() {
  // Outer function code

  function innerFunction() {
    // Inner function code
  }

  // More outer function code

  // You can call the inner function within the outer function
  innerFunction();
}

// Call the outer function
outerFunction();

In this example, `innerFunction` is defined inside `outerFunction`. It has access to its own scope as well as the scope of `outerFunction`. Note that the inner function is only accessible within the outer function, and it's not accessible from outside `outerFunction`.

This pattern is often used for creating private variables or encapsulating functionality within a specific scope. It's a fundamental concept in JavaScript known as "closures."