var ua = {
 "iphone":"iPhone",
 "ipodtouch":"iPod",
 "Googlebot":"Googlebot",
 "yahoobot":"Mozilla/5.0 (compatible; Yahoo! Slurp; http://help.yahoo.com/help/us/ysearch/slurp)",
 "msnbot":"msnbot"
}
function exists_ua()
{
  for(var index in ua) {
    if(navigator.userAgent.indexOf(ua[index])>=0){ return 1; }
  }
  return 0;
}