foo.js

'use strict';

/**
 *  Typical constructor
 */

function Human (props) {
  this.props = props || {};
};

Human.prototype.speak = function () {
  console.log.apply(console, arguments);
};

var tj = new Human({name: 'tj'});

tj.speak('This is a basic JS constructor');


/**
 *  Self constructing constructor?
 */

function Dog (props) {
  if (!(this instanceof Dog)) return new Dog(props);
  this.props = props || {};
};

Dog.prototype.bark = function () {
  console.log.apply(console, arguments);
};

var fido = Dog({name: 'fido'});

fido.bark('I am an annoying dog');