gistfile1.js

function aboveFold(obj) {
    var curtop = 0;
    if (obj.offsetParent) {
        do {
            curtop += obj.offsetTop;
        } while (obj = obj.offsetParent);
    }
    else {
        curtop = obj.offsetTop;
    }
    return curtop < window.pageYOffset + screen.height;
}