$(function() {

  $(window).on("scroll", function() {
    if ($(this).scrollTop() > 100) {
      $(".pagetop").fadeIn("fast");
    } else {
      $(".pagetop").fadeOut("fast");
    }

    scrollHeight = $(document).height();
    scrollPosition = $(window).height() + $(window).scrollTop();
    footHeight = $("footer").innerHeight();

    if ( scrollHeight - scrollPosition  <= footHeight ) {
      $(".pagetop").css({
        "position":"absolute",
      });
    } else {
      $(".pagetop").css({
        "position":"fixed",
      });
    }
  });

});