<p>function getScrollY() {
    scrOfY = 0;
    if( typeof( window.pageYOffset ) == "number" ) {
        scrOfY = window.pageYOffset;
    } else if( document.body &amp;&amp; ( document.body.scrollLeft || document.body.scrollTop ) ) {
        scrOfY = document.body.scrollTop;
    } else if( document.documentElement &amp;&amp; ( document.documentElement.scrollLeft || document.documentElement.scrollTop ) ) {
        scrOfY = document.documentElement.scrollTop;
    }
    return scrOfY;
}

jQuery(function($){
    var upprev_closed = false;
    var upprev_hidden = true;
    $(window).scroll(function() {
        var lastScreen = getScrollY() + $(window).height() </p>