From 552c438ed8a7cc10726a1d82f77e1e9bbfaa37a4 Mon Sep 17 00:00:00 2001
From: Troy Morehouse <troymore@nbnet.nb.ca>
Date: Fri, 24 Nov 2017 16:47:31 -0400
Subject: [PATCH] fix(table): use stable sort algorithm to prevent SSR issues
 (#1399)

* Create stable-sort.js

* add stable sort to utils

* [b-table] use stableSort
---
 src/components/table/table.vue |  4 ++--
 src/utils/index.js             |  2 ++
 src/utils/stable-sort.js       | 28 ++++++++++++++++++++++++++++
 3 files changed, 32 insertions(+), 2 deletions(-)
 create mode 100644 src/utils/stable-sort.js

diff --git a/src/components/table/table.vue b/src/components/table/table.vue
index b2a5c8f3b6f..3c52e187abf 100644
--- a/src/components/table/table.vue
+++ b/src/components/table/table.vue
@@ -62,7 +62,7 @@
 </style>
 
 <script>
-  import { warn, looseEqual, KeyCodes } from '../../utils'
+  import { warn, looseEqual, stableSort, KeyCodes } from '../../utils'
   import { keys, assign } from '../../utils/object'
   import { isArray, concat } from '../../utils/array'
   import { listenOnRootMixin } from '../../mixins'
@@ -712,7 +712,7 @@
         }
         // Apply local Sort
         if (sortBy && localSorting) {
-          items = items.sort(function sortItemsFn(a, b) {
+          items = stableSort(items, function sortItemsFn(a, b) {
             let ret = null
             if (typeof sortCompare === 'function') {
               // Call user provided sortCompare routine
diff --git a/src/utils/index.js b/src/utils/index.js
index 8fb2aa6d245..98a9a912379 100644
--- a/src/utils/index.js
+++ b/src/utils/index.js
@@ -13,6 +13,7 @@ import observeDom from './observe-dom'
 import pluckProps from './pluckProps'
 import prefixPropName from './prefixPropName'
 import { registerComponent, registerComponents, registerDirective, registerDirectives, vueUse } from './plugins'
+import stableSort from './stable-sort'
 import suffixPropName from './suffixPropName'
 import unPrefixPropName from './unPrefixPropName'
 import upperFirst from './upperFirst'
@@ -37,6 +38,7 @@ export {
   registerComponents,
   registerDirective,
   registerDirectives,
+  stableSort,
   suffixPropName,
   upperFirst,
   unPrefixPropName,
diff --git a/src/utils/stable-sort.js b/src/utils/stable-sort.js
new file mode 100644
index 00000000000..1960b188fca
--- /dev/null
+++ b/src/utils/stable-sort.js
@@ -0,0 +1,28 @@
+/*
+ * Consitant and stable sort function across JavsaScript platforms
+ *
+ * Inconsistant sorts can cause SSR problems between client and server
+ * such as in <b-table> if sortBy is applied to the data on server side render.
+ * Chrome and V8 native sorts are inconsistant/unstable
+ *
+ * This function uses native sort with fallback to index compare when the a and b
+ * compare returns 0
+ *
+ * Algorithm bsaed on:
+ * https://stackoverflow.com/questions/1427608/fast-stable-sorting-algorithm-implementation-in-javascript/45422645#45422645
+ *
+ * @param {array} array to sort
+ * @param {function} sortcompare function
+ * @return {array}
+ */
+
+export default function stableSort (array, compareFn) {
+  // Using `.bind(compareFn)` on the wrapped anonymous function improves
+  // performance by avoiding the function call setup. We don't use an arrow
+  // function here as it binds `this` to the `stableSort` context rather than
+  // the `compareFn` context, which wouldn't give us the performance increase.
+  return array
+    .map((a, index) => [ index, a ])
+    .sort(function (a, b) { return this(a[1], b[1]) || a[0] - b[0] }.bind(compareFn))
+    .map(e => e[1])
+}