Javascript object instance vs returned functions

Question

What are the differences in creating objects in javascript between

test = function(a, b){
   this.calculate = function(){
      return a + b;
   }
}
obj = new test(1, 2);
console.log(obj.calculate());

And

test = function(a, b){
   return {
      calculate: function(){
         return a + b;
      }
   }
}
obj = test(1, 2);
console.log(obj.calculate());

I have used both in different situations but never understood the difference, I know that the latter approach has the over head of creating the functions for ever instance but still see it used in a lot of situations, can anyone clarafy this for me? I was unable to find anything about this by searching

The first one also creates the functions for every instance. The only differences is that in the first case, the new instance inherits from test.prototype while in the second case it directly inherits from Object. — Felix Kling
– Felix Kling, Commented Jan 23, 2013 at 9:11
This is a good read on the subject: 2ality.com/2012/01/js-inheritance-by-example.html — Hector Correa
– Hector Correa, Commented Jan 23, 2013 at 14:25

Felix Kling · Accepted Answer · 2013-01-23 09:18:50Z

5

The first one also creates the functions for every instance. The only differences in this situation is that the new instance inherits from test.prototype in the first case, while it directly inherits from Object in the second case.

In the first case it would be easier to let the instances share code, by adding the functions to the prototype. For example:

var Test = function(a, b){
   this._a = a;
   this._b = b;
};

Test.prototype.calculate = function(){
   return this._a + this._b;
};

Since all instances inherit from Test.prototype, the calculate function exists only once and all instances refer to the same function.

answered Jan 23, 2013 at 9:18

Felix Kling

820k181 gold badges1.1k silver badges1.2k bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Alex Ciminian · Accepted Answer · 2013-01-23 09:18:57Z

2

As Felix said in the comment, the difference is the inheritance chain. The first inherits from test.prototype and the second from Object. The consequence is that if you wanted to create the function only once and make every instance share it, you'd have to do something like this:

test = function (a, b) {
  this.a = a;
  this.b = b;
}

test.prototype.calculate = function () {
  return this.a + this.b;
}

answered Jan 23, 2013 at 9:18

Alex Ciminian

11.5k16 gold badges64 silver badges95 bronze badges

1 Comment

Alex Ciminian Over a year ago

:)) I was considering using the exact same notation as you. That would have been fun.

Collectives™ on Stack Overflow

Javascript object instance vs returned functions

2 Answers 2

Comments

1 Comment

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

1 Comment

Your Answer

Sign up or log in

Post as a guest

Related