explicit-binding.js

function doSomething() {
  // "use strict"; // uncomment to run in strict mode
  console.log( this.x );
}

var obj = {
  x: "Hello World!"
}

var x = "global"

// passing the object to be used for `this` explicitly
doSomething.call(obj);   // "Hello World!
doSomething.apply(obj);  // "Hello World!

// passing the `null` and `undefined`, `this` will be bind to global scope
doSomething.call(null);   // "Hello World!
doSomething.apply(null);  // "Hello World!
doSomething.call(undefined);   // "Hello World!
doSomething.apply(undefined);  // "Hello World!