Extending Backbone.collection Prototype

Following on from this question, I'm trying to augment Backbone.Collection with some custom methods. However, I'm getting some inconsistent behaviour between the console and the so

Solution 1:

You are mixing up a few key concepts which is why you aren't seeing the behavior that you expect, which is more a fundamental javascript question and not entirely related to backbone.

Consider the following constructor:

varKlass = function() {};

You can invoke that constuctor using the new keyword to get an instance from that constructor.

var klassInstance = new Klass();

Now, lets say I wanted to add a method that was available to all of the instances that are derivied from that constructor. For that I can use the prototype object.

Klass.prototype.instanceMethod = function() { alert('hi'); };

Then I should be able to invoke that method using the following:

klassInstance.instanceMethod();

However, I can also add a static function – and I use the term loosely in this context – to the constructor itself, which can be invoked without having an instance.

Klass.staticMethod = function() { alert('yo!'); };

This method will be available directly off the constructor, but will not be available – directly – off of instances.

For example:

klassInstance.staticMethod == undefined

So what's really wrong with your test is that you are adding a method to the prototype – a method that will be available to all instances of that "class" – but in your test you are testing for a method directly on the "class" itself. Which is not the same thing.

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An aside, though relevant, Backbone.js provides a built in mechanic to create "sub-classes" of thier built in types. This is the static.extend() method. This provides you a simple way to add your own functionality to the base Backbone classes.

In your case you would want to do something like:

varMyCollection = Backbone.Collection.extend({
    extract: function() {
        // do whatever
    }
}) 

Then, you can create instances of your new classes, which will have an .extract() method on them by saying:

var coll = new MyCollection();
coll.extract();

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TL;DR;

Ultimately – back to your original question – if you want a method that will be available on all instances of a particular class, then your test is incorrect. You either need to new up an instance to test against:

test('extending backbone', function () {
    var col = newBackbone.Collection();
    ok(typeof col.extract == 'function');
});

Or check the prototype directly for a method – this is subtlely different in the fact that the prototype object is not the only for an object to get a method.

test('extending backbone', function () {
    ok(typeofBackbone.Collection.prototype.extract == 'function');
});

Solution 2:

make sure backbone.js and underscore.js is fully loaded before doing the tests.