Javascript Random String

Does anyone have a variable-length random string generator function written in JavaScript?

Found this. Works well:

function getRandomString() {
var chars = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXTZabcdefghiklmnopqrstuvwxyz";
var string_length = 12;
var randomstring = '';
for (var i=0; i<string_length; i++) {
var rnum = Math.floor(Math.random() * chars.length);
randomstring += chars.substring(rnum,rnum+1);
}

return randomstring;
}