function uuid(num) {

    var s = [];

    var hexDigits = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz";

    for (var i = 0; i < num; i++) {

      s[i] = hexDigits.substr(Math.floor(Math.random() * 0x10), 1);

    }

    s[14] = "4";

    s[19] = hexDigits.substr((s[19] & 0x3) | 0x8, 1);

    s[8] = s[13] = s[18] = s[23] = "-";

    var uuid = s.join("");

    return uuid;

}