Why !(this instanceof Object)?

NewObject.js

/* http://stackoverflow.com/questions/22211755/function-f-if-this-instanceof-f-return-new-f,
If constructor is called without 'new' keyword before, it returns a new instance of the object. */

function MyObject(foo){
  if (!(this instanceof MyObject)){
    return new MyObject(foo);
  }
  this.bar = foo;
}

/* Testing... */
var newObject1 = new MyObject('First option');
var newObject2 = MyObject('Second option');
/* So newObject1 and newObject2 are instances of MyObject */