What difference is there in JavaScript between a constructor function, and function returning object which is invoked as a constructor?

Question

I know this is not the recommended way of doing it, but if I declare the following functions, and then invoke them as constructors, what will be the difference (if any) betw

Answer 1

I'd say the most important thing would be the prototype of the returned objects.

  function Something() {
       this.foo = "bar";
  }

  Something.prototype = {
    // Something prototype code
    hello: function(){
     //...
    }
  }

  function something2() {
     var that = {};
     that.foo = "bar";
     return that;
  }

  something2.prototype = {
      // something2 prototype code
      greetings : function() {
      //...
      }
  }

  var x = new Something();
  var y = new something2();
  var z = something2();

  typeof x.hello === function // should be true
  typeof y.greetings === undefined // should be true
  typeof z.greetings === undefined // should be true

In other words, I'd say you're not instantiating objects withe something2, you are creating purely new objects that inherit from Object.

1. Something() will give you new objects of "Something" type when you use the new keyword.
2. something2() will give you new objects of "Object" type, which will immediately return a new empty object.

3. new something2 is inefficient, because you are creating a blank scope, from which you create a new object

   var that = {};
   

   which is equivalent to

   var that = new Object();