object literal notation vs prototype speed and memory

Question

i came across this post http://www.webmasterworld.com/javascript/3066162.htm about how in javascript when you instantiate an object literal if it has methods defined in it then each time one is instantiated its methods are copied as well. so if you have a bunch of instances of the object literal then the copied methods would begin to add up in memory.

how ever he/she states that using prototype to make your methods is more efficient because the methods are not copied for each instance of the constructor object.

is this true? because i was under the impression that prototype allowed you to add properties/methods even after the object was instantiated rather than within the object when its first created.

Answer 1

When you create an object like this:

function Car(c) {
   this.color = c;
   this.drive = function() {};
}

You're actually creating a copy of the drive function for each Car that you create. In Javascript, every object has a prototype pointer and properties/methods from that prototype propagate down the tree to child objects.

When you do:

function Car(c) {this.color=c};
Car.prototype.drive = function {};

and then create a few car objects you end up with this instead:

            {drive: function(){}}
             /        |           \
      car1 (red)    car2 (blue)    car3 (green)

The drive function is shared between all the Car objects. It's a shame the syntax for doing this in Javascript is so awkward.