RFC4122 Version 4 compliant JavaScript GUID generator ripped off from: http://stackoverflow.com/a/2117523/34315.

GuidGenerator.js

function guidGen() {
    return 'xxxxxxxx-xxxx-4xxx-yxxx-xxxxxxxxxxxx'.replace(/[xy]/g, function(c) {
        var r = Math.random()*16|0, v = c == 'x' ? r : (r&0x3|0x8);
        return v.toString(16);
    });
}