See code:
var file1 = \"50.xsl\"; var file2 = \"30.doc\"; getFileExtension(file1); //returns xsl getFileExtension(file2); //returns doc function getFileExt
return filename.replace(/\.([a-zA-Z0-9]+)$/, "$1");
edit: Strangely (or maybe it's not) the $1 in the second argument of the replace method doesn't seem to work... Sorry.
$1