Question

Somebody asked me this question and i was a little lost by it.

As this is a Q&A it makes sense to ask here.

Why would I add a function to an objects prototype rather than add it to the object?

Answer 1

Consider these two objects:

Object 1

var myObject1 = function() {
    this.myProperty = true;
    this.myMethod = function() {
        return this.myProperty;
    };
}

Object 2

var myObject2 = function() {
   this.myProperty = true;
}

myObject2.prototype.myMethod = function() {
    return this.myProperty;
};

Everytime we do this:

var test = new myObject1();

myObject1.myMethod also gets created. Where as when we do this:

var test = new myObject2();

myObject2.myMethod does not have the overhead of needing to be created again because it was added to the prototype chain.

This wouldn’t matter for a few instances but in a game, for example, where there could be hundreds of instances this can be quite a performance hit.

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This net.tutsplus article may explain it better than me http://net.tutsplus.com/tutorials/javascript-ajax/prototypes-in-javascript-what-you-need-to-know/