function getValue(field) {
  var address = location.search.substring(1);
  var startExtract = address.indexOf(field + "=");
  if (startExtract > -1) {
    startExtract = startExtract + field.length + 1;
    var endExtract = address.indexOf("&",startExtract);
    if (endExtract == -1)
      endExtract = address.length;
    return unescape(address.substring(startExtract,endExtract));
  }
  return '';
}