Angular Form validation: alphanumeric

gistfile1.js

.directive('alphanumeric', function() {
    return {
        require: 'ngModel',
        restrict: 'A',
        link: function(scope, elem, attr, ngModel) {

            var validator = function(value) {
                if (/^[a-zA-Z0-9]*$/.test(value)) {
                    ngModel.$setValidity('alphanumeric', true);
                    return value;
                } else {
                    //注意得是若驗證沒通過建議回傳undefined
                    ngModel.$setValidity('alphanumeric', false);
                    return undefined;
                }
            };
            //For DOM -> model validation
            ngModel.$parsers.unshift(validator);
            //For model -> DOM validation
            ngModel.$formatters.unshift(validator);
        }
    };
})