--- a/static/js/backbone.shard.js	Mon Jun 27 18:13:01 2016 +0800
+++ b/static/js/backbone.shard.js	Thu Jun 30 21:47:54 2016 +0800
@@ -1,19 +1,19 @@
 /*
  *      backbone.shard.js.
- * 
- *      (c) 2013 Anton Shestakov.
- * 
+ *
+ *      (c) 2013, 2016 Anton Shestakov.
+ *
  *      This extension to Backbone may be freely distributed
  *      under the MIT license:
- *      http://opensource.org/licenses/mit-license.php
+ *      https://opensource.org/licenses/MIT
  */
 
 Backbone.Shard = function(options) {
     this._collection = options.collection;
     this._filter = options.filter;
-    
+
     this.models = this._collection.filter(this._filter);
-    
+
     this._collection
         .on('all', function(event, model) {
             if (event == 'change') {
@@ -48,25 +48,27 @@
             this.models = this._collection.filter(this._filter);
             this.trigger('reset');
         }, this);
-    
+
     this.initialize.apply(this, arguments);
 };
 
 _.extend(Backbone.Shard.prototype, Backbone.Events, {
     initialize: function() {},
-    
+
     pluck: function(attr) {
         return _.map(this.models, function(model) { return model.get(attr); });
     }
 });
 
 // Underscore methods that we want to implement on the Shard.
-var methods = ['forEach', 'each', 'map', 'collect', 'reduce', 'foldl',
-    'inject', 'reduceRight', 'foldr', 'find', 'detect', 'filter', 'select',
-    'reject', 'every', 'all', 'some', 'any', 'include', 'contains', 'invoke',
-    'max', 'min', 'toArray', 'size', 'first', 'head', 'take', 'initial', 'rest',
-    'tail', 'drop', 'last', 'without', 'indexOf', 'shuffle', 'lastIndexOf',
-    'isEmpty', 'chain'];
+var methods = [
+    'all', 'any', 'chain', 'collect', 'contains', 'detect', 'difference',
+    'drop', 'each', 'every', 'filter', 'find', 'findIndex', 'findLastIndex',
+    'first', 'foldl', 'foldr', 'forEach', 'head', 'include', 'includes',
+    'indexOf', 'initial', 'inject', 'invoke', 'isEmpty', 'last', 'lastIndexOf',
+    'map', 'max', 'min', 'reduce', 'reduceRight', 'reject', 'rest', 'sample',
+    'select', 'shuffle', 'size', 'some', 'tail', 'take', 'toArray', 'without'
+];
 
 // Mix in each Underscore method as a proxy to `Shard#models`.
 _.each(methods, function(method) {
@@ -78,7 +80,7 @@
 });
 
 // Underscore methods that take a property name as an argument.
-var attributeMethods = ['groupBy', 'countBy', 'sortBy'];
+var attributeMethods = ['countBy', 'groupBy', 'indexBy', 'sortBy'];
 
 // Use attributes instead of properties.
 _.each(attributeMethods, function(method) {