ngModel.$parsers ingore whitespace at the end of ng-model value

I have directive like this:

我有这样的指示:

  .directive('noWhitespace', ['$parse', function($parse) {
    return {
      restrict: 'A',
      require: 'ngModel',
      link: function (scope, element, attrs, ngModel) {
        /*
        scope.$watch(attrs.ngModel, function(value) {
          var getter = $parse(value);
          update(getter(scope));
        });
        */
        function update(viewValue) {
          console.log(JSON.stringify(viewValue));
          if (viewValue.match(/\s/)) {
            ngModel.$setValidity('whitespace', false);
            return undefined;
          } else {
            ngModel.$setValidity('whitespace', true);
            return viewValue;
          }
        }
        ngModel.$parsers.unshift(update);
      }
    };
  }])
  .dir