Fix the back button in Chrome iOS (#383)

* Fix the back button in Chrome iOS

* Remove extraneous date in CHANGES.md

Author: tptee

CHANGES.md

@@ -1,3 +1,7 @@
+## HEAD
+
+- Fix the back button on Chrome iOS
+
 ## [v4.4.0]
 > Nov 1, 2016
 

modules/DOMUtils.js

@@ -43,3 +43,12 @@ export const supportsPopStateOnHashChange = () =>
  */
 export const supportsGoWithoutReloadUsingHash = () =>
   window.navigator.userAgent.indexOf('Firefox') === -1
+
+/**
+ * Returns true if a given popstate event is an extraneous WebKit event.
+ * Accounts for the fact that Chrome on iOS fires real popstate events
+ * containing undefined state when pressing the back button.
+ */
+export const isExtraneousPopstateEvent = event =>
+  event.state === undefined &&
+  navigator.userAgent.indexOf('CriOS') === -1

modules/createBrowserHistory.js

@@ -9,7 +9,8 @@ import {
   removeEventListener,
   getConfirmation,
   supportsHistory,
-  supportsPopStateOnHashChange
+  supportsPopStateOnHashChange,
+  isExtraneousPopstateEvent
 } from './DOMUtils'
 
 const PopStateEvent = 'popstate'
@@ -79,8 +80,9 @@ const createBrowserHistory = (props = {}) => {
   }
 
   const handlePopState = (event) => {
-    if (event.state === undefined)
-      return // Ignore extraneous popstate events in WebKit.
+    // Ignore extraneous popstate events in WebKit.
+    if (isExtraneousPopstateEvent(event))
+      return 
 
     handlePop(getDOMLocation(event.state))
   }