ClOSURES IN JAVASCRIPT

WHAT IS CLOSURES IN JAVASCRIPT?

A closure is when a function remembers and has access to variables from its outer scope even after the outer function has finished executing.

Simple example

function outer() {
let name = "John";

function inner(){
console.log(name);
}

return inner;
}

const myFunction = outer();

myFunction();

Output:

John

why does this work?

Normally, you might think name should disappear after outer() finishes.

But inner() remembers the name variable.

outer()
  |
  |-- name = "John"
  |
  |-- inner()
        |
        |-- remembers "John"

That remembering ability is called a closure.

One more useful example

Closures are often used to create private variables:

function counter() {
let count = 0;

return function () {
count++;
console.log(count);
};
}

const myCounter = counter();

myCounter(); // 1
myCounter(); // 2
myCounter(); // 3

Even though counter() has already finished, the returned function still remembers count.

So:

Closure = A function + the variables from its surrounding environment that it remembers.