.bind - JavaScript

fn.bind.js

/**
 * The bind() method creates a new function that, when called,
 * has its this keyword set to the provided value,
 * with a given sequence of arguments preceding any
 * provided when the new function is called.
 */

 this.x = 9;    // this refers to global "window" object here in the browser
 var module = {
   x: 81,
   getX: function() { return this.x; }
 };

 module.getX(); // 81

 var retrieveX = module.getX;
 console.log(retrieveX());
 // returns 9 - The function gets invoked at the global scope

 // Create a new function with 'this' bound to module
 // New programmers might confuse the
 // global var x with module's property x
 var boundGetX = retrieveX.bind(module);
 console.log(boundGetX()); // 81