See code:
var file1 = \"50.xsl\";
var file2 = \"30.doc\";
getFileExtension(file1); //returns xsl
getFileExtension(file2); //returns doc
function getFileExt
function func() {
var val = document.frm.filename.value;
var arr = val.split(".");
alert(arr[arr.length - 1]);
var arr1 = val.split("\\");
alert(arr1[arr1.length - 2]);
if (arr[1] == "gif" || arr[1] == "bmp" || arr[1] == "jpeg") {
alert("this is an image file ");
} else {
alert("this is not an image file");
}
}