backbone.js: does calling collection.reset() removes the models as well?

Question

I read in the backbone documentation that calling collection.reset() clears the collection. I want to know if it removes the models as well or do they continue to live in memory?

If they're not removed is there an easier way to remove all the models in a collection without iterating through the models and calling model.remove()?

Answer 1

You could listen for the reset event from the model and do your cleanup and this.destroy() in response. That's what the event hooks are for. See http://backbonejs.org/#Events-catalog

Note: You absolutely should not change or override any method or property prefixed by an underscore, such as _removeReference. The underscores mean that it is intended as an internal method or property, and that the internal implementations may change (their API's are considered unstable). Upgrading Backbone could break any code that relies on underscore-prefixed methods, even if the release is advertised as a backwards-compatible change.

I know your question says "without iterating", but it really is the most reliable way of handling this. Consider a case where a model has been moved from one collection to another, but it's still listening on the first collection's reset event (because a programmer six months later didn't notice the connection).

Now when the first collection gets reset, the moved model gets destroyed. Oops!

Iterating over the collection probably is the best way to handle this if you don't have an endpoint on your API that will delete all objects in a collection in batch on the API server (which is often how this is handled).

Luckily, that iteration is pretty easy:

destroyAll: function () {
  var promises = [];

  while(this.models.length > 0) {
    promises.push( this.models[0].destroy() );
  }

  // handle errors communicating with the server
  $.when(promises).fail(function (response) {
    this.trigger('syncError',
      response);
  }.bind(this));
}

Answer 2

What you are looking for is, probably, for the models to be garbage-collected. That is, that nobody has a reference to these models anymore, after they are removed from the collection.

Backbone does its part of removing the references that it set on the models, when they are removed from the collection. However, you have to do your own cleanup if your code has references to those models. Most of the time, this happens if those models are registered as event listeners, like in this example: http://jsfiddle.net/dira/4uxp4/2/

Taking a look at the implementation of reset, you could change _removeReference to call a cleanup function on the model as well. And in the model, remove the model from all the listeners/all the other objects that keep a reference to it.