What is a JavaScript closure? Can you give me an example?

What is a JavaScript closure? Can you give me an example?

A JavaScript closure is a function that retains access to its lexical scope, even when the function is executed outside that scope. For example, consider this code:

function outerFunction() {
    let outerVariable = 'I am outside!';
    function innerFunction() {
        console.log(outerVariable);
    }
    return innerFunction;
}

const closureFunction = outerFunction();
closureFunction(); // This will log: 'I am outside!'

Why is it useful to use closures?

Closures are useful for data encapsulation, allowing you to create private variables and functions. They help in maintaining state in asynchronous programming and can be used to create factory functions.

Can you give me another example of a closure?

Sure! Here's another example:

function makeCounter() {
    let count = 0;
    return function() {
        count += 1;
        return count;
    };
}

const counter = makeCounter();
console.log(counter()); // 1
console.log(counter()); // 2

This creates a counter that retains its state.

What are some common use cases for closures?

Common use cases for closures include creating private variables, implementing the module pattern, and managing asynchronous code, such as callbacks and promises.