MD Settings: Minor refactor of settings-animated-pages

chrome/browser/resources/settings/settings_page/settings_animated_pages.js

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 /**
  * @fileoverview
  * 'settings-animated-pages' is a container for a page and animated subpages.
  * It provides a set of common behaviors and animations.
  *
  * Example:
@@ skipping 60 matching lines @@
     if (!this.queuedRouteChange_)
       return;
     this.async(this.currentRouteChanged_.bind(
         this,
         this.queuedRouteChange_.newRoute,
         this.queuedRouteChange_.oldRoute));
   },
 
   /** @private */
   currentRouteChanged_: function(newRoute, oldRoute) {
+    if (newRoute.section == this.section && newRoute.subpage.length > 0) {

[michaelpg, 2016/08/01 08:37:14]

this saves some work, since all <settings-animated-pages> on the page run this
whenever the route changes. most of them will fail this and just set |selected|
to 'main' (which is almost always a no-op)

+      this.switchToSubpage_(newRoute, oldRoute);
+    } else {
+      this.$.animatedPages.exitAnimation = 'fade-out-animation';
+      this.$.animatedPages.entryAnimation = 'fade-in-animation';
+      this.$.animatedPages.selected = 'main';
+    }
+  },
+
+  /**
+   * Selects the subpage specified by |newRoute|.
+   * @param {!settings.Route} newRoute
+   * @param {!settings.Route} oldRoute
+   * @private
+   */
+  switchToSubpage_: function(newRoute, oldRoute) {
     // Don't manipulate the light DOM until it's ready.
     if (!this.lightDomReady_) {
       this.queuedRouteChange_ = this.queuedRouteChange_ || {oldRoute: oldRoute};
       this.queuedRouteChange_.newRoute = newRoute;
       return;
     }
 
-    var newRouteIsSubpage = newRoute && newRoute.subpage.length;
-    var oldRouteIsSubpage = oldRoute && oldRoute.subpage.length;
+    this.ensureSubpageInstance_();
 
-    if (newRouteIsSubpage)
-      this.ensureSubpageInstance_();
-
-    if (!newRouteIsSubpage || !oldRouteIsSubpage ||
-        newRoute.subpage.length == oldRoute.subpage.length) {
-      // If two routes are at the same level, or if either the new or old route
-      // is not a subpage, fade in and out.
-      this.$.animatedPages.exitAnimation = 'fade-out-animation';
-      this.$.animatedPages.entryAnimation = 'fade-in-animation';
-    } else {
-      // For transitioning between subpages at different levels, slide.
-      if (newRoute.subpage.length > oldRoute.subpage.length) {
+    if (oldRoute) {
+      var oldRouteIsSubpage = oldRoute.subpage.length > 0;
+      if (oldRouteIsSubpage && oldRoute.contains(newRoute)) {
+        // Slide left for a descendant subpage.
         this.$.animatedPages.exitAnimation = 'slide-left-animation';
         this.$.animatedPages.entryAnimation = 'slide-from-right-animation';
-      } else {
+      } else if (newRoute.contains(oldRoute)) {
+        // Slide right for an ancestor subpage.
         this.$.animatedPages.exitAnimation = 'slide-right-animation';
         this.$.animatedPages.entryAnimation = 'slide-from-left-animation';
+      } else {
+        // The old route is not a subpage or is at the same level, so just fade.
+        this.$.animatedPages.exitAnimation = 'fade-out-animation';
+        this.$.animatedPages.entryAnimation = 'fade-in-animation';
+
+        if (!oldRouteIsSubpage) {
+          // Set the height the expand animation should start at before
+          // beginning the transition to the new subpage.
+          // TODO(michaelpg): Remove MainPageBehavior's dependency on this
+          // height being set.
+          this.style.height = this.clientHeight + 'px';
+        }
       }
     }
 
-    if (newRouteIsSubpage && newRoute.section == this.section) {
-      if (!oldRouteIsSubpage) {
-        // Set the height the expand animation should start at before beginning
-        // the transition to the new sub-page.
-        // TODO(michaelpg): Remove MainPageBehavior's dependency on this height
-        // being set.
-        this.style.height = this.clientHeight + 'px';
-      }
-      this.$.animatedPages.selected = newRoute.subpage.slice(-1)[0];
-    } else {
-      this.$.animatedPages.selected = 'main';
-    }
+    this.$.animatedPages.selected = newRoute.subpage.slice(-1)[0];
   },
 
   /**
    * Ensures that the template enclosing the subpage is stamped.
    * @private
    */
   ensureSubpageInstance_: function() {
     var id = this.currentRoute.subpage.slice(-1)[0];
     var template = Polymer.dom(this).querySelector(
         'template[name="' + id + '"]');
 
     // Nothing to do if the subpage isn't wrapped in a <template> or the
     // template is already stamped.
     if (!template || template.if)
       return;
 
     // Set the subpage's id for use by neon-animated-pages.
     var subpage = /** @type {{_content: DocumentFragment}} */(template)._content
         .querySelector('settings-subpage');
     if (!subpage.id)
       subpage.id = id;
 
     // Render synchronously so neon-animated-pages can select the subpage.
     template.if = true;
     template.render();
   },
 });