feat(rating): make widget accessible

 * Support keyboard navigation.
 * Add WAI-ARIA markup.
 * Text representation for screen readers.

Source: http://mindtrove.info/creating-an-accessible-internationalized-dojo-rating-widget/

Closes #1707

src/rating/rating.js

@@ -23,38 +23,41 @@ angular.module('ui.bootstrap.rating', [])
   };
 
   this.buildTemplateObjects = function(states) {
-    var defaultOptions = {
-      stateOn: this.stateOn,
-      stateOff: this.stateOff
-    };
-
     for (var i = 0, n = states.length; i < n; i++) {
-      states[i] = angular.extend({ index: i }, defaultOptions, states[i]);
+      states[i] = angular.extend({ index: i }, { stateOn: this.stateOn, stateOff: this.stateOff }, states[i]);
     }
     return states;
   };
 
   $scope.rate = function(value) {
-    if ( !$scope.readonly ) {
+    if ( !$scope.readonly && value >= 0 && value <= $scope.range.length ) {
       ngModelCtrl.$setViewValue(value);
       ngModelCtrl.$render();
     }
   };
 
   $scope.enter = function(value) {
     if ( !$scope.readonly ) {
-      $scope.val = value;
+      $scope.value = value;
     }
     $scope.onHover({value: value});
   };
 
   $scope.reset = function() {
-    $scope.val = ngModelCtrl.$viewValue;
+    $scope.value = ngModelCtrl.$viewValue;
     $scope.onLeave();
   };
 
+  $scope.onKeydown = function(evt) {
+    if (/(37|38|39|40)/.test(evt.which)) {
+      evt.preventDefault();
+      evt.stopPropagation();
+      $scope.rate( $scope.value + (evt.which === 38 || evt.which === 39 ? 1 : -1) );
+    }
+  };
+
   this.render = function() {
-    $scope.val = ngModelCtrl.$viewValue;
+    $scope.value = ngModelCtrl.$viewValue;
   };
 }])
 

src/rating/test/rating.spec.js

@@ -27,24 +27,34 @@ describe('rating directive', function () {
     return state;
   }
 
+  function triggerKeyDown(keyCode) {
+    var e = $.Event('keydown');
+    e.which = keyCode;
+    element.trigger(e);
+  }
+
   it('contains the default number of icons', function() {
     expect(getStars().length).toBe(5);
+    expect(element.attr('aria-valuemax')).toBe('5');
   });
 
   it('initializes the default star icons as selected', function() {
     expect(getState()).toEqual([true, true, true, false, false]);
+    expect(element.attr('aria-valuenow')).toBe('3');
   });
 
   it('handles correctly the click event', function() {
     getStar(2).click();
     $rootScope.$digest();
     expect(getState()).toEqual([true, true, false, false, false]);
     expect($rootScope.rate).toBe(2);
+    expect(element.attr('aria-valuenow')).toBe('2');
 
     getStar(5).click();
     $rootScope.$digest();
     expect(getState()).toEqual([true, true, true, true, true]);
     expect($rootScope.rate).toBe(5);
+    expect(element.attr('aria-valuenow')).toBe('5');
   });
 
   it('handles correctly the hover event', function() {
@@ -68,20 +78,23 @@ describe('rating directive', function () {
     $rootScope.$digest();
 
     expect(getState()).toEqual([true, true, false, false, false]);
+    expect(element.attr('aria-valuenow')).toBe('2');
   });
 
   it('shows different number of icons when `max` attribute is set', function() {
     element = $compile('<rating ng-model="rate" max="7"></rating>')($rootScope);
     $rootScope.$digest();
 
     expect(getStars().length).toBe(7);
+    expect(element.attr('aria-valuemax')).toBe('7');
   });
 
   it('shows different number of icons when `max` attribute is from scope variable', function() {
     $rootScope.max = 15;
     element = $compile('<rating ng-model="rate" max="max"></rating>')($rootScope);
     $rootScope.$digest();
     expect(getStars().length).toBe(15);
+    expect(element.attr('aria-valuemax')).toBe('15');
   });
 
   it('handles readonly attribute', function() {
@@ -124,6 +137,43 @@ describe('rating directive', function () {
     expect($rootScope.leaving).toHaveBeenCalled();
   });
 
+  describe('keyboard navigation', function() {
+    it('supports arrow keys', function() {
+      triggerKeyDown(38);
+      expect($rootScope.rate).toBe(4);
+
+      triggerKeyDown(37);
+      expect($rootScope.rate).toBe(3);
+      triggerKeyDown(40);
+      expect($rootScope.rate).toBe(2);
+
+      triggerKeyDown(39);
+      expect($rootScope.rate).toBe(3);
+    });
+
+    it('can get zero value but not negative', function() {
+      $rootScope.rate = 1;
+      $rootScope.$digest();
+
+      triggerKeyDown(37);
+      expect($rootScope.rate).toBe(0);
+
+      triggerKeyDown(37);
+      expect($rootScope.rate).toBe(0);
+    });
+
+    it('cannot get value above max', function() {
+      $rootScope.rate = 4;
+      $rootScope.$digest();
+
+      triggerKeyDown(38);
+      expect($rootScope.rate).toBe(5);
+
+      triggerKeyDown(38);
+      expect($rootScope.rate).toBe(5);
+    });
+  });
+
   describe('custom states', function() {
     beforeEach(inject(function() {
       $rootScope.classOn = 'icon-ok-sign';
@@ -150,7 +200,8 @@ describe('rating directive', function () {
     }));
 
     it('should define number of icon elements', function () {
-      expect(getStars().length).toBe($rootScope.states.length);
+      expect(getStars().length).toBe(4);
+      expect(element.attr('aria-valuemax')).toBe('4');
     });
 
     it('handles each icon', function() {

template/rating/rating.html

@@ -1,3 +1,5 @@
-<span ng-mouseleave="reset()">
-    <i ng-repeat="r in range" ng-mouseenter="enter($index + 1)" ng-click="rate($index + 1)" class="glyphicon" ng-class="$index < val && (r.stateOn || 'glyphicon-star') || (r.stateOff || 'glyphicon-star-empty')"></i>
+<span ng-mouseleave="reset()" ng-keydown="onKeydown($event)" tabindex="0" role="slider" aria-valuemin="0" aria-valuemax="{{range.length}}" aria-valuenow="{{value}}">
+    <i ng-repeat="r in range" ng-mouseenter="enter($index + 1)" ng-click="rate($index + 1)" class="glyphicon" ng-class="$index < value && (r.stateOn || 'glyphicon-star') || (r.stateOff || 'glyphicon-star-empty')">
+        <span class="sr-only">({{ $index < value ? '*' : ' ' }})</span>
+    </i>
 </span>