UUIDinJS

UUID.js

// UUID/Guid Generator - http://frugalcoder.us/post/2012/01/13/javascript-guid-uuid-generator.aspx
// use: UUID.create() or UUID.createSequential()
// convenience:  UUID.empty, UUID.tryParse(string)
(function(w){
  // From http://baagoe.com/en/RandomMusings/javascript/
  // Johannes Baagøe <baagoe@baagoe.com>, 2010
  function Mash() {
    var n = 0xefc8249d;

    var mash = function(data) {
    data = data.toString();
    for (var i = 0; i < data.length; i++) {
      n += data.charCodeAt(i);
      var h = 0.02519603282416938 * n;
      n = h >>> 0;
      h -= n;
      h *= n;
      n = h >>> 0;
      h -= n;
      n += h * 0x100000000; // 2^32
    }
    return (n >>> 0) * 2.3283064365386963e-10; // 2^-32
    };

    mash.version = 'Mash 0.9';
    return mash;
  }

  // From http://baagoe.com/en/RandomMusings/javascript/
  function Kybos() {
    return (function(args) {
    // Johannes Baagøe <baagoe@baagoe.com>, 2010
    var s0 = 0;
    var s1 = 0;
    var s2 = 0;
    var c = 1;
    var s = [];
    var k = 0;

    var mash = Mash();
    var s0 = mash(' ');
    var s1 = mash(' ');
    var s2 = mash(' ');
    for (var j = 0; j < 8; j++) {
      s[j] = mash(' ');
    }

    if (args.length == 0) {
      args = [+new Date];
    }
    for (var i = 0; i < args.length; i++) {
      s0 -= mash(args[i]);
      if (s0 < 0) {
      s0 += 1;
      }
      s1 -= mash(args[i]);
      if (s1 < 0) {
      s1 += 1;
      }
      s2 -= mash(args[i]);
      if (s2 < 0) {
      s2 += 1;
      }
      for (var j = 0; j < 8; j++) {
      s[j] -= mash(args[i]);
      if (s[j] < 0) {
        s[j] += 1;
      }
      }
    }

    var random = function() {
      var a = 2091639;
      k = s[k] * 8 | 0;
      var r = s[k];
      var t = a * s0 + c * 2.3283064365386963e-10; // 2^-32
      s0 = s1;
      s1 = s2;
      s2 = t - (c = t | 0);
      s[k] -= s2;
      if (s[k] < 0) {
      s[k] += 1;
      }
      return r;
    };
    random.uint32 = function() {
      return random() * 0x100000000; // 2^32
    };
    random.fract53 = function() {
      return random() +
      (random() * 0x200000 | 0) * 1.1102230246251565e-16; // 2^-53
    };
    random.addNoise = function() {
      for (var i = arguments.length - 1; i >= 0; i--) {
      for (j = 0; j < 8; j++) {
        s[j] -= mash(arguments[i]);
        if (s[j] < 0) {
        s[j] += 1;
        }
      }
      }
    };
    random.version = 'Kybos 0.9';
    random.args = args;
    return random;

    } (Array.prototype.slice.call(arguments)));
  };

  var rnd = Kybos();

  // UUID/GUID implementation from http://frugalcoder.us/post/2012/01/13/javascript-guid-uuid-generator.aspx
  var UUID = {
    "empty": "00000000-0000-0000-0000-000000000000"
    ,"parse": function(input) {
      var ret = input.toString().trim().toLowerCase().replace(/^[\s\r\n]+|[\{\}]|[\s\r\n]+$/g, "");
      if ((/[a-f0-9]{8}\-[a-f0-9]{4}\-[a-f0-9]{4}\-[a-f0-9]{4}\-[a-f0-9]{12}/).test(ret))
        return ret;
      else
        throw new Error("Unable to parse UUID");
    }
    ,"createSequential": function() {
      var ret = new Date().valueOf().toString(16).replace("-","")
      for (;ret.length < 12; ret = "0" + ret);
      ret = ret.substr(ret.length-12,12); //only least significant part
      for (;ret.length < 32;ret += Math.floor(rnd() * 0xffffffff).toString(16));
      return [ret.substr(0,8), ret.substr(8,4), "4" + ret.substr(12,3), "89AB"[Math.floor(Math.random()*4)] + ret.substr(16,3),  ret.substr(20,12)].join("-");
    }
    ,"create": function() {
      var ret = "";
      for (;ret.length < 32;ret += Math.floor(rnd() * 0xffffffff).toString(16));
      return [ret.substr(0,8), ret.substr(8,4), "4" + ret.substr(12,3), "89AB"[Math.floor(Math.random()*4)] + ret.substr(16,3),  ret.substr(20,12)].join("-");
    }
    ,"random": function() {
      return rnd();
    }
    ,"tryParse": function(input) {
      try {
        return UUID.parse(input);
      } catch(ex) {
        return UUID.empty;
      }
    }
  };
  UUID["new"] = UUID.create;

  w.UUID = w.Guid = UUID;
}(window || this));

Have you thought about maybe trying to use some randomness from the system instead of creating it algorithmically e.g. use setTimeout? something sort of like this:

 var now = new Date().getTime() - (Math.random(10)*1000);setTimeout(function() { var then = new Date().getTime() * 1000; console.log("randomness", then - now); }, Math.random(90));

for me this for example is generating random numbers pretty nicely: https://gist.github.com/3753902 it's hacky to use setTimeout, but I figure that should be a good source of randomness...