zig Tryit Editor

<!DOCTYPE html>
<html>
<script src="../../ajax.googleapis.com/ajax/libs/angularjs/1.6.9/angular.min.js"></script>
<body>
<script>
  var app = angular.module("myShoppingList", []);
  app.controller("myCtrl", function ($scope) {
    $scope.products = ["Milk", "Bread", "Cheese"];
    $scope.addItem = function () {
      $scope.errortext = "";
      if (!$scope.addMe) { return; }
      if ($scope.products.indexOf($scope.addMe) == -1) {
        $scope.products.push($scope.addMe);
      } else {
        $scope.errortext = "The item is already in your shopping list.";
      }
    }
    $scope.removeItem = function (x) {
      $scope.errortext = "";
      $scope.products.splice(x, 1);
    }
  });
</script>
<div ng-app="myShoppingList" ng-controller="myCtrl">
  <ul>
    <li ng-repeat="x in products">{{x}}<span ng-click="removeItem($index)">×</span></li>
  </ul>
  <input ng-model="addMe">
  <button ng-click="addItem()">Add</button>
  <p>{{errortext}}</p>
</div>
<p>Try to add the same item twice, and you will get an error message.</p>
</body>

</html>