Closure is nothing but a technique bringing out the variable to the outer scope so that parent scope can also work with the variable from child scope.

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

let doo = foo();

console.log(doo());
console.log(doo());
console.log(doo());
console.log(count);

Here count variable can be mutated from the outer scope.
But count variable cannot be accessed directly from outside the foo function.