fix(dropdown): fix up arrow nav support

* add support for when user opens dropdown and then presses the up arrow key.

Fixes angular-ui#4327

src/dropdown/dropdown.js

@@ -292,16 +292,19 @@ angular.module('ui.bootstrap.dropdown', ['ui.bootstrap.position'])
               break;
             }
             case (38): { // Up
-              dropdownCtrl.selectedOption = dropdownCtrl.selectedOption === 0 ?
-                0 : dropdownCtrl.selectedOption - 1;
+              if (!angular.isNumber(dropdownCtrl.selectedOption)) {
+                dropdownCtrl.selectedOption = elems.length - 1;
+              } else {
+                dropdownCtrl.selectedOption = dropdownCtrl.selectedOption === 0 ?
+                  0 : dropdownCtrl.selectedOption - 1;
+              }
               break;
             }
           }
           elems[dropdownCtrl.selectedOption].focus();
         }
       });
     }
-
   };
 })
 

src/dropdown/test/dropdown.spec.js

@@ -587,6 +587,17 @@ describe('dropdownToggle', function() {
       expect(isFocused(focusEl)).toBe(false);
     });
 
+    it('should focus last list element when up arrow pressed after dropdown toggled', function() {
+      $document.find('body').append(element);
+      clickDropdownToggle();
+      expect(element.hasClass(dropdownConfig.openClass)).toBe(true);
+
+      triggerKeyDown($document, 38);
+      var elems = element.find('ul').eq(0).find('a');
+      var focusEl = elems.eq(elems.length - 1);
+      expect(isFocused(focusEl)).toBe(true);
+    });
+
     it('should not focus any list element when down arrow pressed if closed', function() {
       $document.find('body').append(element);
       triggerKeyDown($document, 40);