Add at end perf improvement can only occur if no sorting occurred

Sorting requires reappending of all children.  Rather than handling all of the various flag states to determine this, we can simply remove the added views cache if a sort occurs.

Author: paulfalgout

src/next-collection-view.js

@@ -368,6 +368,9 @@ const CollectionView = Backbone.View.extend({
 
     if (!viewComparator) { return; }
 
+    // If children are sorted prevent added to end perf
+    delete this._addedViews;
+
     this.triggerMethod('before:sort', this);
 
     this.children._sort(viewComparator, this);
@@ -427,21 +430,14 @@ const CollectionView = Backbone.View.extend({
     return this;
   },
 
-  _isAddedAtEnd(addedView, index, addedViews) {
-    const viewIndex = this.children._views.length - addedViews.length + index;
-    return addedView === this.children._views[viewIndex];
-  },
-
   _filterChildren() {
     const viewFilter = this._getFilter();
     const addedViews = this._addedViews;
 
     delete this._addedViews;
 
     if (!viewFilter) {
-      if (!this.sortWithCollection && addedViews && _.every(addedViews, _.bind(this._isAddedAtEnd, this))) {
-        return addedViews;
-      }
+      if (addedViews) { return addedViews; }
 
       return this.children._views;
     }
@@ -621,8 +617,11 @@ const CollectionView = Backbone.View.extend({
       return view;
     }
 
+    // Only cache views if added to the end
+    if (!index || index >= this.children.length) {
+      this._addedViews = [view];
+    }
     this._addChild(view, index);
-    this._addedViews = [view];
     this._showChildren();
 
     return view;

test/unit/next-collection-view/collection-view-data.spec.js

@@ -209,7 +209,7 @@ describe('next CollectionView Data', function() {
     let myCollectionView;
     let collection;
 
-    describe('when sortWithCollection is true', function() {
+    describe('when children are sorted', function() {
       beforeEach(function() {
         collection = new Backbone.Collection([{ id: 1 }, { id: 2 }, { id: 3 }]);
 
@@ -233,11 +233,11 @@ describe('next CollectionView Data', function() {
       });
     });
 
-    describe('when sortWithCollection is false', function() {
+    describe('when children are not sorted', function() {
       beforeEach(function() {
         collection = new Backbone.Collection([{ id: 1 }, { id: 2 }, { id: 3 }]);
 
-        myCollectionView = new MyCollectionView({ collection, sortWithCollection: false });
+        myCollectionView = new MyCollectionView({ collection, viewComparator: false });
         myCollectionView.render();
       });