Call async service in AngularJS custom validation directive

Question

I have a directive for custom validation (verify a username doesn\'t already exist). The validation uses the $http service to ask the server if the username exists, so the

Answer 1

In order to get this to work, I needed to add "return value;" outside of the asynchronous call. Code below.

commonModule.directive("usernameVerify", [
    'userSvc', function(userSvc) {
        return {
            require: 'ngModel',
            scope: false,
            link: function(scope, element, attrs, ctrl) {
                ctrl.$parsers.unshift(checkForAvailability);
                ctrl.$formatters.unshift(checkForAvailability);

                function checkForAvailability(value) {
                    if (value.length < 5) {
                        return value;
                    }
                    userSvc.userExists(value)
                        .success(function(alreadyUsed) {
                            var valid = alreadyUsed === 'false';
                            if (valid) {
                                ctrl.$setValidity('usernameVerify', true);
                                return value;
                            }
                            ctrl.$setValidity('usernameVerify', false);
                            return undefined;
                        });
                    // Below is the added line of code.
                    return value;
                }
            }
        }
    }
]);

Answer 2

Angular has a dedicated array of $asyncValidators for precisely this situation:

see https://docs.angularjs.org/api/ng/type/ngModel.NgModelController

ngModel.$asyncValidators.uniqueUsername = function(modelValue, viewValue) {
var value = modelValue || viewValue;

// Lookup user by username
return $http.get({url:'/api/users/' + value}).
   then(function resolved() {
     //username exists, this means validation fails
     return $q.reject('exists');
   }, function rejected() {
     //username does not exist, therefore this validation passes
     return true;
   });
};