Check my channel subscription

Question

I'm developing a form for registration. The form can only be seen if the user is already enrolled in youtube.

I tried using script but I get Error: Permission denied access to property "document" would aid thanks.

setTimeout( function(){
        if($('#validyoutube iframe').length){
            var validframe = $('#validyoutube iframe');
            $(validframe).ready(function() {
                if ($(validframe).contents().find('#yt-subscribe button').attr('data-is-subscribed')) {
                    alert('Si Existe el atributo');
                }
                else{
                    alert('No Existe atibuto');
                }
            });
        }
        else{
            alert('no existe');
        }
    },5000);