Backbone.js: sortable collection

SortableCollection.js

var SortableCollection = Backbone.Collection.extend({
	
	//key: 'LocalStorageKey',	// define a key for saving sort info to local storage
	
	//defaultSort: 'some_key',	// the default key to sort by
	defaultDesc: false,
	
	localStoreKey: function(extra){
		return 'list:'+this.key+(extra?':'+extra:'');
	},
/*
	Sort Key - defaults to "release date" 
*/
	sortKey: function(newKey){
		
		if(newKey !== undefined)
			amplify.store('list:'+this.key+':sort', newKey);
		else
			return amplify.store('list:'+this.key+':sort') || this.defaultSort;
	},

/*
	Sort Descending
*/
	sortDesc: function(desc){
		
		if(desc !== undefined)
			return amplify.store('list:'+this.key+':sort:desc', desc);
		else
			return amplify.store('list:'+this.key+':sort:desc') || this.defaultDesc;
	},
	
/*
	Sort By - overriding default sort by behaviour to add in reverse order logic
*/
	sortBy: function(){
		
		var models = _.sortBy(this.models, this.comparator, this);
		
		if(this.sortDesc())
			models.reverse();
	
		return models;
	},
	
/*
	Comparator - How to sort;
*/
	comparator: function(model){	
		return model.get( this.sortKey() );
	},
	
/*
	Change how this collection is sorted
*/
	changeSort: function(sortKey){
		
		// if same sort key was clicked, lets reverse the sort direction
		if(this.sortKey() == sortKey)
			this.sortDesc( !this.sortDesc() ); // set direction to opposite of what it is now
		
		// set the new sort key
		this.sortKey( sortKey );
		
		this.trigger('sort:change');
		
		// re-sort the collection
		this.sort();
	}
	
});

http://www.benknowscode.com/2013/12/multi-column-sort-in-backbone-collections.html