Solution: In memory counter with controller

<script src="angular.min.js"></script>
<script>
angular.module("CounterApp", [])
    .controller("CounterController", ['$scope', function($scope) {
        $scope.counter = 0;
        $scope.increment = function() {
            $scope.message = "";
            $scope.counter++;
        };
        $scope.decrement = function() {
            if ($scope.counter > 0) {
                $scope.counter--;
            } else {
                $scope.message = "We cannot go below 0";
            }
        };
}])
</script>
<div ng-app="CounterApp">
    <div ng-controller="CounterController">
        <button ng-click="increment()">Increment</button>
        <button ng-click="decrement()">Decrement</button>
        <div>{{counter}}</div>
        <div>{{message}}</div>
    </div>
</div>