Backbone collection live filtering (untested)

livefilter.js

Backbone.Collection.prototype.liveFilter = function(attributes) {
	// Make a clone of the collection instantiated with all the filtered items
	var _org = this;
	var _new = new this.constructor(this.where(attributes));
	// What happens when you add to the original collection?
	_org.on('add', function(model) {
		// Unless one of the attributes doesn't match
		for (key in attributes) {
			if (model.get(key) !== attributes[key]) return;
		}
		// Add the model to our new collection
		_new.add(model);
	});
	_org.on('remove', function(model) {
		for (key in attributes) {
			if (model.get(key) !== attributes[key]) return;
		}
		_new.remove(model);
	});
	_new.on('add', function(model) {
		for (key in attributes) {
			if (model.get(key) !== attributes[key]) return;
		}
		_org.add(model);
	});
	_new.on('remove', function(model) {
		for (key in attributes) {
			if (model.get(key) !== attributes[key]) return;
		}
		_org.remove(model);
	});
}