React to a model change inside of controller using $watch (angular.js)

controller-test.js

    // professional.fullName validation, $watch looks at our model
    // If our field's value is less than 4, we set the formElementErrorState variable to true
    $scope.$watch("professional.fullName", function(newValue, oldValue) {
      if ($scope.professional.fullName.length < 4) {
        $scope.formElementErrorState = true;
      }
    });