Closure in JavaScript

Local bindings are created anew for every call, and different calls can’t affect on another calls local bindings.

function wrapValue(n) {
  let local = n;
  return () => local;
}
 
let wrap1 = wrapValue(1);
let wrap2 = wrapValue(2);
console.log(wrap1());
console.log(wrap2());

A function that references bindings from local scopes around it is called a closure. This behavior not only frees you from having to worry about lifetimes of bindings but also makes it possible to use function values in some creative ways.

function multiplier(factor) {
  return number => number * factor;
}
 
let twice = multiplier(2);
 
console.log(twice(5));