Limit file uploads by extension

Nice & easy! A great JS Script... I'm keeping the credits, this ain't mine!

<SCRIPT LANGUAGE="JavaScript">
<!-- Original:  ArjoGod, Shauna Merritt -->
<!-- Modified By:  Ronnie T. Moore, Editor -->

<!-- This script and many more are available free online at -->
<!-- The JavaScript Source!! http://javascript.internet.com -->

<!-- Begin
extArray = new Array(".jpg");
function LimitAttach(form, file) {
allowSubmit = false;
if (!file) return;
while (file.indexOf("\\") != -1)
file = file.slice(file.indexOf("\\") + 1);
ext = file.slice(file.indexOf(".")).toLowerCase();
for (var i = 0; i < extArray.length; i++) {
if (extArray[i] == ext) { allowSubmit = true; break; }
}
if (allowSubmit) form.submit();
else
alert("Please only upload files that end in types:  "
+ (extArray.join("  ")) + "\nPlease select a new "
+ "file to upload and submit again.");
}
//  End -->
</script>

And to make it work, just apply it on the submit input

<input type="submit" onclick="LimitAttach(this.form, this.form.input_file_name.value)" />