function getDocumentHeight() {
  var D = document;
  return Math.max(
    Math.max(D.body.scrollHeight, D.documentElement.scrollHeight),
    Math.max(D.body.offsetHeight, D.documentElement.offsetHeight),
    Math.max(D.body.clientHeight, D.documentElement.clientHeight)
  );
}

function getViewportHeight() {
  var viewportwidth;
  var viewportheight;

  // the more standards compliant browsers (mozilla/netscape/opera/IE7) use window.innerWidth and window.innerHeight

  if (typeof window.innerWidth != 'undefined')
  {
    viewportwidth = window.innerWidth,
    viewportheight = window.innerHeight
  }

  // IE6 in standards compliant mode (i.e. with a valid doctype as the first line in the document)

  else if (typeof document.documentElement != 'undefined'
    && typeof document.documentElement.clientWidth !=
    'undefined' && document.documentElement.clientWidth != 0)
  {
    viewportwidth = document.documentElement.clientWidth,
    viewportheight = document.documentElement.clientHeight
  }

  // older versions of IE
  else
  {
       viewportwidth = document.getElementsByTagName('body')[0].clientWidth,
       viewportheight = document.getElementsByTagName('body')[0].clientHeight
  }
  //document.write('<p>Your viewport width is '+viewportwidth+'x'+viewportheight+'</p>');
  return viewportheight;
}

/* TopLink setzen, wenn Dokument größer als Viewport */
if(getDocumentHeight()-4 > getViewportHeight()) {
  //var topLink = document.createElement("a");
  //var topLinkText = document.createTextNode("zum Seitenanfang");
  //topLink.href="#container";
  //topLink.appendChild(topLinkText);
  if(document.getElementById('top-link')) { document.getElementById('top-link').style.display='block'; }
}