angular animations not working for ng-show when changing class using ng-class

Question

I want to create a slider for some objects that are contained in an unordered list, using ng-show and animations. I have this working well when the objects are sliding in one direction.

However, when I want the user to be able to slide objects left or right, using ng-class to change the class, the animations no longer work.

The html for the left/right case is:

<div class="slide-holder">
  <ul class="slide-list">
    <li class="slide-object" ng-show="directionElement == 0" ng-class="{'slide-object-left': direction === 'left', 'slide-object-right': direction === 'right'}">
      Hello There 1! How are you?</li>
    <li class="slide-object" ng-show="directionElement == 1" ng-class="{'slide-object-left': direction === 'left', 'slide-object-right': direction === 'right'}">
      Hello There 2! How are you?</li>
    <li class="slide-object" ng-show="directionElement == 2" ng-class="{'slide-object-left': direction === 'left', 'slide-object-right': direction === 'right'}">
      Hello There 3! How are you?</li>
    <li class="slide-object" ng-show="directionElement == 3" ng-class="{'slide-object-left': direction === 'left', 'slide-object-right': direction === 'right'}">
      Hello There 4! How are you?</li>
  </ul>
</div>

The functions in the controller for changing the direction are:

$scope.left = function() {
  $scope.direction === 'left'
  if($scope.directionElement > 0)
    $scope.directionElement = $scope.directionElement - 1;
};

$scope.right = function() {
  $scope.direction === 'right'
  if($scope.directionElement < 3)
  $scope.directionElement = $scope.directionElement + 1;
};

The transitions css looks like this:

.slide-object-left.ng-hide-add,
.slide-object-left.ng-hide-remove {
  -webkit-transition:0.5s linear all;
  -moz-transition:0.5s linear all;
  -o-transition:0.5s linear all;
  transition:0.5s linear all;

  position:absolute;
}

.slide-object-left.ng-hide-add {
  left:100%;
}

.slide-object-left.ng-hide-remove,
.slide-object-left.ng-hide-add.ng-hide-add-active {
  left:0;
}

.slide-object-left.ng-hide-remove.ng-hide-remove-active {
  left:-100%;
}

I have created a plnkr to show both cases: http://plnkr.co/edit/sh0uCAPZiCne4Y5ynFQ2?p=preview

EDIT 1: I've updated the plnkr to fix the '===' mistake in the controller which was causing the switching of direction to malfunction, as per the answer by Theoretisch. However, the main ng-class problem and animation problem remains. Here is the update plnkr: http://plnkr.co/edit/lv1BBFjRoOmenTv7IBeC?p=preview

Answer 1

The reason why the animation isn't working is because the === in the functions of your controller.

Instead of the === you should use just = because you don't want to compare $scope.direction with your string.

$scope.left = function() {
  $scope.direction = 'left'
  if($scope.directionElement > 0)
    $scope.directionElement = $scope.directionElement - 1;
};

$scope.right = function() {
  $scope.direction = 'right'
  if($scope.directionElement < 3)
  $scope.directionElement = $scope.directionElement + 1;
};

Now the animation works again. But there are some more things to do if you want a good and correct animation. One of them e.g. is to change your css. If you slow down your animation you can see that the wrong slide-object is animated.

Just change this to correct it:

.slide-object-left.ng-hide-add {
  right:-100%;
}

.slide-object-left.ng-hide-remove,
.slide-object-left.ng-hide-add.ng-hide-add-active {
  right:0;
}

.slide-object-left.ng-hide-remove.ng-hide-remove-active {
  right:100%;
}

.slide-object-right.ng-hide-add {
  left:-100%;
}

.slide-object-right.ng-hide-remove,
.slide-object-right.ng-hide-add.ng-hide-add-active {
  left:0%;
}

.slide-object-right.ng-hide-remove.ng-hide-remove-active {
  left:100%;
}

I switched right to left and changed additionally the algebraic sign. You can find the plunk with my changes HERE.

EDIT: I'm not sure why the animation is so buggy. I think it is because the ng-class. I deleted it and edited your ng-show. You can see the edited Plunk HERE. It's not the best solution, but it solves your problem for now I hope. (Maybe you can improve it with THIS fiddle)