How to determine whether a user has a flash player installed on their system using java script.

<script language="javascript">
var plugin = (navigator.mimeTypes && navigator.mimeTypes["application/x-shockwave-flash"] ?
navigator.mimeTypes["application/x-shockwave-flash"].enabledPlugin : 0);
if (plugin &&
parseInt(plugin.description.substring(plugin.description.indexOf(".")-1)) >=
4) { alert("Flash 4 or greater is available")} else { alert("Flash 4 is not available")}
</script>