feat(dropdown): focus toggle element when opening or closing with Esc`

 * Improve accessibility.

Closes #1908.

src/dropdown/dropdown.js

@@ -36,6 +36,7 @@ angular.module('ui.bootstrap.dropdown', [])
 
   var escapeKeyBind = function( evt ) {
     if ( evt.which === 27 ) {
+      openScope.focusToggleElement();
       closeDropdown();
     }
   };
@@ -71,17 +72,24 @@ angular.module('ui.bootstrap.dropdown', [])
     return scope.isOpen;
   };
 
-  scope.$watch('isOpen', function( value ) {
-    $animate[value ? 'addClass' : 'removeClass'](self.$element, openClass);
+  scope.focusToggleElement = function() {
+    if ( self.toggleElement ) {
+      self.toggleElement[0].focus();
+    }
+  };
 
-    if ( value ) {
+  scope.$watch('isOpen', function( isOpen ) {
+    $animate[isOpen ? 'addClass' : 'removeClass'](self.$element, openClass);
+
+    if ( isOpen ) {
+      scope.focusToggleElement();
       dropdownService.open( scope );
     } else {
       dropdownService.close( scope );
     }
 
-    setIsOpen($scope, value);
-    toggleInvoker($scope, { open: !!value });
+    setIsOpen($scope, isOpen);
+    toggleInvoker($scope, { open: !!isOpen });
   });
 
   $scope.$on('$locationChangeSuccess', function() {
@@ -112,6 +120,8 @@ angular.module('ui.bootstrap.dropdown', [])
         return;
       }
 
+      dropdownCtrl.toggleElement = element;
+
       var toggleDropdown = function(event) {
         event.preventDefault();
         event.stopPropagation();

src/dropdown/test/dropdown.spec.js

@@ -20,9 +20,13 @@ describe('dropdownToggle', function() {
     element.trigger(e);
   };
 
+  var isFocused = function(elm) {
+    return elm[0] === document.activeElement;
+  };
+
   describe('basic', function() {
     function dropdown() {
-      return $compile('<li class="dropdown"><a dropdown-toggle></a><ul><li>Hello</li></ul></li>')($rootScope);
+      return $compile('<li class="dropdown"><a href dropdown-toggle></a><ul><li>Hello</li></ul></li>')($rootScope);
     }
 
     beforeEach(function() {
@@ -44,10 +48,13 @@ describe('dropdownToggle', function() {
       expect(element.hasClass('open')).toBe(false);
     });
 
-    it('should close on escape key', function() {
+    it('should close on escape key & focus toggle element', function() {
+      $document.find('body').append(element);
       clickDropdownToggle();
       triggerKeyDown($document, 27);
       expect(element.hasClass('open')).toBe(false);
+      expect(isFocused(element.find('a'))).toBe(true);
+      element.remove();
     });
 
     it('should not close on backspace key', function() {
@@ -170,7 +177,7 @@ describe('dropdownToggle', function() {
   describe('`is-open`', function() {
     beforeEach(function() {
       $rootScope.isopen = true;
-      element = $compile('<li class="dropdown" is-open="isopen"><a dropdown-toggle></a><ul><li>Hello</li></ul></li>')($rootScope);
+      element = $compile('<li class="dropdown" is-open="isopen"><a href dropdown-toggle></a><ul><li>Hello</li></ul></li>')($rootScope);
       $rootScope.$digest();
     });
 
@@ -188,6 +195,18 @@ describe('dropdownToggle', function() {
       $rootScope.$digest();
       expect(element.hasClass('open')).toBe(false);
     });
+
+    it('focus toggle element when opening', function() {
+      $document.find('body').append(element);
+      clickDropdownToggle();
+      $rootScope.isopen = false;
+      $rootScope.$digest();
+      expect(isFocused(element.find('a'))).toBe(false);
+      $rootScope.isopen = true;
+      $rootScope.$digest();
+      expect(isFocused(element.find('a'))).toBe(true);
+      element.remove();
+    });
   });
 
   describe('`on-toggle`', function() {