module.exports = function () {
  var s = [], itoh = '0123456789ABCDEF';
 
  // Make array of random hex digits. The UUID only has 32 digits in it, but we
  // allocate an extra items to make room for the '-'s we'll be inserting.
  for (var i = 0; i <36; i++) s[i] = Math.floor(Math.random()*0x10);
 
  // Conform to RFC-4122, section 4.4
  s[14] = 4;  // Set 4 high bits of time_high field to version
  s[19] = (s[19] & 0x3) | 0x8;  // Specify 2 high bits of clock sequence
 
  // Convert to hex chars
  for (var i = 0; i <36; i++) s[i] = itoh[s[i]];
 
  // Insert '-'s
  s[8] = s[13] = s[18] = s[23] = '-';
 
  return s.join('');
}