Using arguments in flexible constructor

arguments-flexible-constructor.js

function MyConstructor(foo, bar){
  if (!(this instanceof MyConstructor)){
    var obj = Object.create(MyConstructor.prototype);
    return MyConstructor.apply(obj, arguments);
  }
  this.foo = foo;
  this.bar = bar;
  return this;
}

var instance1 = MyConstructor('foo1', 'bar1');
var instance2 = new MyConstructor('foo2', 'bar2');

console.log([instance1.foo, instance1.bar]);
console.log([instance2.foo, instance2.bar]);

instance1.foo = 'whatever';

console.log([instance1.foo, instance1.bar]);
console.log([instance2.foo, instance2.bar]);

console.log(instance1 instanceof MyConstructor);
console.log(instance2 instanceof MyConstructor);