Angular directive for validating a spanish bank account number (SICA)

gistfile1.js

define(['app/main'], function (app) {
    app.register.directive('isSica', function () {
        return {
            restrict: 'A',
            require: 'ngModel',
            link: function (scope, elem, attr, ngModel) {
                function controlDigit(input) {
                    var weights = [1, 2, 4, 8, 5, 10, 9, 7, 3, 6];
                    var sum = 0;
                    for (var i = 0; i < weights.length; i++) {
                        sum += Number(input.charAt(i)) * weights[i];
                    }
                    switch (11 - (sum % 11)) {
                        case 11: return 0;
                        case 10: return 1;
                        default: return 11 - sum % 11;
                    }
                }

                function isValidSICA(sica) {
                    return sica.Entity != undefined && sica.Entity.length === 4 &&
                        sica.Branch != undefined && sica.Branch.length === 4 &&
                        sica.ControlDigit != undefined && sica.ControlDigit.length === 2 &&
                        sica.Account != undefined && sica.Account.length === 10 &&
                        sica.ControlDigit === (controlDigit("00" + sica.Entity + sica.Branch).toString() + controlDigit(sica.Account).toString());
                }

                scope.$watch(attr.isSica, function (newVal, oldVal) {
                    if (newVal != undefined) ngModel.$setValidity('isSica', isValidSICA(newVal));
                }, true);
            }
        };
    });
});