How JavaScript new operator works

JavaScript-new-operator.js

// constructor definition
var Foo = function() {
  // when invoked with new it's as if the following implicitly happens
  // Foo.prototype = {};
  // this = {};
  // return this;
};

// create new instance with 'new'
var x = new Foo();

// create new instance without 'new'
// Above is almost equivalent to 
var y = {};
// illustration purposes only. __proto__ should not be accessed directly
y.__proto__ = Foo.prototype;
y.constructor = Foo;
y.constructor();

x.constructor === y.constructor // true
x instanceof Foo // true
y instanceof Foo // true