Closures are an interesting idea in programming. They help us understand how long variables last and where they can be used.

What Is Variable Scope?

In programming, scope means where you can use a variable. A closure allows a function to remember where it was made, even if it runs outside of that place.

For example, if you have a function inside another function, the inner function can use the variables from the outer function. This is called lexical scoping.

What Is Variable Lifetime?

The lifetime of a variable is how long that variable can be used in memory. With closures, if a variable is created in an outer function, it sticks around as long as the inner function still exists. This means that even if the outer function has finished running, the variables can still hold their values when we call the closure.

Here's a simple example:

function outerFunction() {
    let count = 0;
    
    return function innerFunction() {
        count++;
        return count;
    };
}

const counter = outerFunction();
console.log(counter()); // Outputs: 1
console.log(counter()); // Outputs: 2

In this example, the count variable stays alive and keeps updating each time we call innerFunction. This shows how closures help us understand both variable scope and lifetime. They allow us to use smart programming tricks, like keeping track of information over time.