fix(carousel): reset $currentTransition when no slides

- Reset `$currentTransition` when there are no slides

Closes #4532
Fixes #4390

src/carousel/carousel.js

@@ -122,6 +122,7 @@ angular.module('ui.bootstrap.carousel', [])
   };
 
   $scope.$watch('interval', restartTimer);
+  $scope.$watchCollection('slides', resetTransition);
   $scope.$on('$destroy', resetTimer);
 
   function restartTimer() {
@@ -148,6 +149,12 @@ angular.module('ui.bootstrap.carousel', [])
     }
   }
 
+  function resetTransition(slides) {
+    if (!slides.length) {
+      $scope.$currentTransition = null;
+    }
+  }
+
   $scope.play = function() {
     if (!isPlaying) {
       isPlaying = true;

src/carousel/test/carousel.spec.js

@@ -45,7 +45,7 @@ describe('carousel', function() {
     });
 
     function testSlideActive(slideIndex) {
-      for (var i=0; i<scope.slides.length; i++) {
+      for (var i = 0; i < scope.slides.length; i++) {
         if (i == slideIndex) {
           expect(scope.slides[i].active).toBe(true);
         } else {
@@ -143,7 +143,7 @@ describe('carousel', function() {
     });
 
     it('should hide navigation when only one slide', function () {
-      scope.slides=[{active:false,content:'one'}];
+      scope.slides = [{active:false,content:'one'}];
       scope.$apply();
       elm = $compile(
           '<uib-carousel interval="interval" no-transition="true">' +
@@ -302,7 +302,7 @@ describe('carousel', function() {
     });
 
     it('should change dom when you reassign ng-repeat slides array', function() {
-      scope.slides=[{content:'new1'},{content:'new2'},{content:'new3'}];
+      scope.slides = [{content:'new1'},{content:'new2'},{content:'new3'}];
       scope.$apply();
       var contents = elm.find('div.item');
       expect(contents.length).toBe(3);
@@ -339,6 +339,21 @@ describe('carousel', function() {
       expect($interval.cancel).toHaveBeenCalled();
     });
 
+    it('issue 4390 - should reset the currentTransition if there are no slides', function() {
+      var carouselScope = elm.children().scope();
+      var next = elm.find('a.right');
+      scope.slides = [{content:'new1'},{content:'new2'},{content:'new3'}];
+      scope.$apply();
+
+      testSlideActive(0);
+      carouselScope.$currentTransition = true;
+
+      scope.slides = [];
+      scope.$apply();
+
+      expect(carouselScope.$currentTransition).toBe(null);
+    });
+
     describe('slide order', function() {
 
       beforeEach(function() {