fix($browser): account for IE deserializing history.state on each read

IE 10-11+ deserialize history.state on every read, causing simple comparisons
against history.state always return false. Account for that caching
`history.state` on every hashchange or popstate event.

Also, prevent firing onUrlChange callbacks twice if both popstate and hashchange
event were fired.

Closes angular#9587
Refs angular#9545

Author: mgol

src/ng/browser.js

@@ -123,11 +123,13 @@ function Browser(window, document, $log, $sniffer) {
   // URL API
   //////////////////////////////////////////////////////////////
 
-  var lastBrowserUrl = location.href,
-      lastHistoryState = history.state,
+  var cachedState, lastHistoryState,
+      lastBrowserUrl = location.href,
       baseElement = document.find('base'),
       reloadLocation = null;
 
+  cacheState();
+
   /**
    * @name $browser#url
    *
@@ -165,7 +167,7 @@ function Browser(window, document, $log, $sniffer) {
       // Don't change anything if previous and current URLs and states match. This also prevents
       // IE<10 from getting into redirect loop when in LocationHashbangInHtml5Url mode.
       // See https://github.com/angular/angular.js/commit/ffb2701
-      if (lastBrowserUrl === url && (!$sniffer.history || history.state === state)) {
+      if (lastBrowserUrl === url && (!$sniffer.history || cachedState === state)) {
         return;
       }
       var sameBase = lastBrowserUrl && stripHash(lastBrowserUrl) === stripHash(url);
@@ -174,9 +176,10 @@ function Browser(window, document, $log, $sniffer) {
       // due to a bug in IE10/IE11 which leads
       // to not firing a `hashchange` nor `popstate` event
       // in some cases (see #9143).
-      if ($sniffer.history && (!sameBase || history.state !== state)) {
+      if ($sniffer.history && (!sameBase || cachedState !== state)) {
         history[replace ? 'replaceState' : 'pushState'](state, '', url);
-        lastHistoryState = history.state;
+        lastHistoryState = cachedState;
+        cachedState = state;
       } else {
         if (!sameBase) {
           reloadLocation = url;
@@ -208,20 +211,40 @@ function Browser(window, document, $log, $sniffer) {
    * @returns {object} state
    */
   self.state = function() {
-    return isUndefined(history.state) ? null : history.state;
+    return cachedState;
   };
 
   var urlChangeListeners = [],
       urlChangeInit = false;
 
+  function cacheStateAndFireUrlChange() {
+    cacheState();
+    fireUrlChange();
+  }
+
+  // This variable should be used *only* inside the cacheState function.
+  var lastCachedState = null;
+  function cacheState() {
+    // This should be the only place in $browser where `history.state` is read.
+    cachedState = window.history.state;
+    cachedState = isUndefined(cachedState) ? null : cachedState;
+
+    // Prevent callbacks fo fire twice if both hashchange & popstate were fired.
+    if (equals(cachedState, lastCachedState)) {
+      cachedState = lastCachedState;
+    }
+    lastCachedState = cachedState;
+  }
+
   function fireUrlChange() {
-    if (lastBrowserUrl === self.url() && lastHistoryState === history.state) {
+    if (lastBrowserUrl === self.url() && lastHistoryState === cachedState) {
       return;
     }
 
     lastBrowserUrl = self.url();
+    lastHistoryState = cachedState;
     forEach(urlChangeListeners, function(listener) {
-      listener(self.url(), history.state);
+      listener(self.url(), cachedState);
     });
   }
 
@@ -254,9 +277,9 @@ function Browser(window, document, $log, $sniffer) {
       // changed by push/replaceState
 
       // html5 history api - popstate event
-      if ($sniffer.history) jqLite(window).on('popstate', fireUrlChange);
+      if ($sniffer.history) jqLite(window).on('popstate', cacheStateAndFireUrlChange);
       // hashchange event
-      jqLite(window).on('hashchange', fireUrlChange);
+      jqLite(window).on('hashchange', cacheStateAndFireUrlChange);
 
       urlChangeInit = true;
     }