feat(tabs): replaces unnecessary watches with getter/setter syntax for improved performance

Author: Robert Messerle

src/components/tabs/js/tabsController.js

@@ -7,20 +7,21 @@ angular
  */
 function MdTabsController ($scope, $element, $window, $timeout, $mdConstant, $mdTabInkRipple,
                            $mdUtil, $animate) {
-  var ctrl      = this,
-      locked    = false,
-      elements  = getElements(),
-      queue     = [],
-      destroyed = false,
-      loaded    = false;
+  var ctrl       = this,
+      locked     = false,
+      elements   = getElements(),
+      queue      = [],
+      destroyed  = false,
+      loaded     = false;
+
+  defineProperty('focusIndex', handleFocusIndexChange, $scope.selectedIndex || 0);
+  defineProperty('offsetLeft', handleOffsetChange, 0);
+  defineProperty('hasContent', handleHasContent, false);
 
   ctrl.scope = $scope;
   ctrl.parent = $scope.$parent;
   ctrl.tabs = [];
   ctrl.lastSelectedIndex = null;
-  ctrl.focusIndex = $scope.selectedIndex || 0;
-  ctrl.offsetLeft = 0;
-  ctrl.hasContent = false;
   ctrl.hasFocus = false;
   ctrl.lastClick = true;
   ctrl.shouldPaginate = false;
@@ -47,9 +48,6 @@ function MdTabsController ($scope, $element, $window, $timeout, $mdConstant, $md
 
   function init () {
     $scope.$watch('selectedIndex', handleSelectedIndexChange);
-    $scope.$watch('$mdTabsCtrl.focusIndex', handleFocusIndexChange);
-    $scope.$watch('$mdTabsCtrl.offsetLeft', handleOffsetChange);
-    $scope.$watch('$mdTabsCtrl.hasContent', handleHasContent);
     angular.element($window).on('resize', handleWindowResize);
     angular.element(elements.paging).on('DOMSubtreeModified', ctrl.updateInkBarStyles);
     angular.element(elements.paging).on('DOMSubtreeModified', updatePagination);
@@ -286,6 +284,17 @@ function MdTabsController ($scope, $element, $window, $timeout, $mdConstant, $md
 
   //-- Utility methods
 
+  function defineProperty (key, handler, value) {
+    Object.defineProperty(ctrl, key, {
+      get: function () { return value; },
+      set: function (newValue) {
+        var oldValue = value;
+        value = newValue;
+        handler(newValue, oldValue);
+      }
+    });
+  }
+
   function updatePagination () {
     ctrl.shouldPaginate = shouldPaginate();
     ctrl.shouldCenterTabs = shouldCenterTabs();