Add Collection#sortBy method

Sorts the collection by the given attribute of each item.

Collection#sortBy will trigger a 'update' event on the collection, making views update automatically.

Example:

  @collection = new Serenade.Collection([{name:'Jonas'}, {name:'CJ'}])
  @collection.sortBy('name')
  @collection.get(0) # Returns the `{name:'CJ'}` object

spec/collection.spec.coffee

@@ -42,6 +42,18 @@ describe 'Serenade.Collection', ->
       @collection.sort()
       expect(@collection).toHaveReceivedEvent('update')
 
+  describe '#sortBy', ->
+    it 'updates the order of the items in the collection', ->
+      item1 = {name: 'CJ', age: 30}
+      item2 = {name: 'Anders', age: 37}
+      @collection.update([item1, item2])
+
+      @collection.sortBy('age')
+      expect(@collection.list).toEqual([item1, item2])
+
+      @collection.sortBy('name')
+      expect(@collection.list).toEqual([item2, item1])
+
   describe '#push', ->
     it 'adds an item to the collection', ->
       @collection.push('g')

src/collection.coffee

@@ -28,6 +28,8 @@ class exports.Collection
   sort: (fun) ->
     @list.sort(fun)
     @trigger("update", @list)
+  sortBy: (attribute) ->
+    @sort((a, b) -> if a[attribute] < b[attribute] then -1 else 1)
   forEach: (fun) ->
     forEach(@list, fun)
   map: (fun) ->