From cd8734c3d0a084c13857508c0beed2737bb0a60f Mon Sep 17 00:00:00 2001
From: Paul Falgout <paul@otterball.com>
Date: Fri, 13 Oct 2017 15:13:26 +0900
Subject: [PATCH] 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.
---
 src/next-collection-view.js                     | 17 ++++++++---------
 .../collection-view-data.spec.js                |  6 +++---
 2 files changed, 11 insertions(+), 12 deletions(-)

diff --git a/src/next-collection-view.js b/src/next-collection-view.js
index 5cc09f4f6c..7010534d86 100644
--- a/src/next-collection-view.js
+++ b/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);
@@ -427,11 +430,6 @@ 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;
@@ -439,9 +437,7 @@ const CollectionView = Backbone.View.extend({
     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;
diff --git a/test/unit/next-collection-view/collection-view-data.spec.js b/test/unit/next-collection-view/collection-view-data.spec.js
index 977dbe38c6..2b69fdd306 100644
--- a/test/unit/next-collection-view/collection-view-data.spec.js
+++ b/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();
       });