Time-based UUID v4 compliant generator (RFC4122 compliant)

uuid.js

function uuid() {
  var uuid = "", i, random;
  for (i = 0; i < 32; i++) {
    random = Math.random() * 16 | 0;
    if (i == 8 || i == 12 || i == 16 || i == 20) uuid += "-"
    uuid += (i == 12 ? 4 : (i == 16 ? (random & 3 | 8) : random)).toString(16)
  }
  return uuid
}