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))