function guid() {
  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);
  });
}
Creates a GUID.
    See: https://en.wikipedia.org/wiki/Globally_unique_identifier
    Original author: broofa (http://www.broofa.com/)
    Sourced from: http://stackoverflow.com/a/2117523/4949715
@return {string} A pseudo-random GUID.