来自行为树b3库的创建 UUID js版本

/**
 * This function is used to create unique IDs for trees and nodes.
 * 
 * (consult http://www.ietf.org/rfc/rfc4122.txt).
 *
 * @method createUUID
 * @return {String} A unique ID.
**/
b3.createUUID = function() {
    var s = [];
    var hexDigits = "0123456789abcdef";
    for (var i = 0; i < 36; i++) {
        s[i] = hexDigits.substr(Math.floor(Math.random() * 0x10), 1);
    }
    // bits 12-15 of the time_hi_and_version field to 0010
    s[14] = "4";

    // bits 6-7 of the clock_seq_hi_and_reserved to 01
    s[19] = hexDigits.substr((s[19] & 0x3) | 0x8, 1);

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

    var uuid = s.join("");
    return uuid;
}