Clean Code in JavaScript

Closures

Inner scopes, as we've seen, have access to the variables of outer scopes:

function outer() {  let thing = 123;  function inner() {    // I can access `thing` within here!    thing; // => 123  }  inner();}outer();

What naturally follows from this is the concept of a closure. A closure is how JavaScript enables you to continue to access the scope of an inner function regardless of where or when it is called.

It's simplest to think of a closure as simply a retained scope. A closure is a wrapped-up or enclosed scope that is passed around alongside the function, invisibly. When you call the function, it has implicit access to its scope provided by this closure.

Consider the following function (fn), which returns another function. It has its own ...