How to override Backbone.sync?

Take a look at this annotated source example where they overwrite Backbone.sync with a localstorage alternative

backbone-localStorage

Basically Backbone.sync should be a function that takes 4 arguments:

Backbone.sync = function(method, model, options) { };

You need to fire either options.success or options.error depending on whether the method succeeded. The methods are in the format:

• "create" : expected that you create the model on the server
• "read" : expected that you read this model from the server and return it
• "update" : expected that you update the model on the server with the argument
• "delete" : expected that you delete the model from the server.

You need to implement those 4 methods and define whatever you want for your "server"

Of course these are only the things that Backbone.sync must implement. You may implement more methods and you may pass more paramaters back to success but it's best not to do this.

It's best to make sure it does the same as Backbone.sync does currently so that your programming to an interface rather then an implementation. If you want to switch out your modified Backbone.sync for say the localStorage one you won't have to extend it yourself to match your extended Backbone.sync"

[Edit]

Also do note that you can use multiple implementations of sync. Every reference to Backbone.sync is actaully (this.sync || Backbone.sync) so you just have to do something like:

var MyModel = Backbone.Model.extend({ 
    ...

    "sync": myOwnSpecificSync,

    ...
});

Backbone.sync is just the default global one that all models use unless the models have a sync method specifically set.

I know this answer is a bit too late, and the answer from @Raynos is great, but I did it a bit differently, and maybe it would be useful for you or for any other person trying to use an API with Backbone.

Instead of overriding Backbone.sync, I overrided Backbone.ajax, because it's where the ajax request is made.

Here's an example :

// Set the default implementation of `Backbone.ajax` to proxy through to `$`.
Backbone.ajax = function() {
    var args = Array.prototype.slice.call(arguments, 0);

    // Here, I add the OAuth token (or any other token)
    // But before, I check that data exists, if not I add it
    if (args[0]['data'] === undefined) {
        args[0]['data'] = {};
    }
    args[0]['data']['token'] = 'any_api_token_here';

    return Backbone.$.ajax.apply(Backbone.$, args);
};