Regular Expression Alphanumeric & Underscore

[barkster]

I'm trying to do a regex to allow only alphanumeric and the underscore but I can't get it to work.  I've tested on a few reg testers and it worked there but I can't get it to work on my page.

 

 

javascript

var rah = new RegExp(/([^A-Za-z0-9_])/);

if (!rah.test(f.tbgalleryname.value)) {

alert("Your folder name has illegal characters.\nCan only contain alphanumeric characters (a-z 0-9 _)");

return false;

}