AngularJS phone number validation directive

validation.js

(function () {
    'use strict';
    
    var phonePattern = /^\+{0,1}[\d ()-]+$/;
    
    app.directive('phoneNumber', function () {
        return {
            require: 'ngModel',
            link: function (scope, elm, attrs, ctrl) {
                ctrl.$validators.phoneNumber = function (modelValue, viewValue) {
                    if (ctrl.$isEmpty(modelValue)) {
                        return true;
                    }

                    if (phonePattern.test(viewValue)) {
                        return true;
                    }

                    return false;
                };
            }
        };
    });

})();