I have JavaScript code Problem find, How To solve?

See This Error http://prntscr.com/qi68v3 - You can also see it by inspecting it. Url: https://www.hindihelpguru.com/what-is-referral-code-information-hindi/

    // When the user scrolls down 20px from the top of the document, show the button
    window.onscroll = function() {
        scrollFunction()
    };

    function scrollFunction() {
        if (document.body.scrollTop > 20 || document.documentElement.scrollTop > 20) {
            document.getElementById("Btnmy").style.display = "block";
        } else {
            document.getElementById("Btnmy").style.display = "none";
        }
    }

    // When the user clicks on the button, scroll to the top of the document
    function topFunction() {
        document.body.scrollTop = 0;
        document.documentElement.scrollTop = 0;
    }

If you have a solution for this error, please send me the code Editing again. I do not have much knowledge of coding.