JavaScript code to detect user os

I have this code to detect visitors operating system.

<script>var OSName="Unknown OS";
  if (navigator.appVersion.indexOf("Win")!=-1) OSName="Windows";
  if (navigator.appVersion.indexOf("Mac")!=-1) OSName="MacOS";
  if (navigator.appVersion.indexOf("X11")!=-1) OSName="UNIX";
  if (navigator.appVersion.indexOf("Linux")!=-1) OSName="Linux";

  document.write('Your OS: '+OSName);
</script>

But it detecta as Linux in Android phone I want to detect Android, windows, Linux,j2me,Mac and iOS Operating Systems