scrollTop() not working on mobile browser

Question

This code works as expected on desktop but it doesn't work on mobile browsers

$(document).ready(function() {
    $(window).scroll(function() {
        if ($(window).width() < 690) {
            if ($(window).scrollTop() > 800) {
                $('.contact').fadeIn(500);
            }
            if ($(window).scrollTop() < 800) { 
                $('.contact').fadeOut(500);
            }
        }
    });
});