Sample directive to set default button click using Angular JS in ASP.NET webforms app

app-default-button.js

var app = angular.module("app", []);

app = app.directive('appDefaultButton', function () {
    return function (scope, element, attr, ctrl) {
        
        // This is all standard directive code copied from ng-sanitize
        // The point of it is store & track 
        //    if passed value was changed & re-run
        
        element.addClass('app-default-button')
            .data('$appDefaultButton', attr.appDefaultButton);

        scope.$watch(attr.appDefaultButton, 
                     function appDefaultButtonWatchAction(value) {
            
            if (!document || !document.forms) {
                return;
            }
                         
            document.forms[0].action =
                 // instead of URL, run some JS
                 // if we don't do "void()", 
                 //    Firefox replaces all page with return 
                 'javascript:void(' + 
                 // wrap the button with angular, and trigger click
                 'angular.element(document.getElementById("' + 
                    value + '"))'+ '.triggerHandler("click")' +
                 ');'; // closing the "void(" part
        });
    };
});