function v1({ node = [ 0x00, 0x00, 0x00, 0x00, 0x00, 0x00 ], clockseq = 0, msecs = Date.now(), nsecs = 0 }) {
  const b = new Array(16);
  
  clockseq = clockseq & 0x3fff;

  // Per 4.1.4 - Convert from unix epoch to Gregorian epoch
  msecs += 12219292800000;

  // `time_low`
  const tl = ((msecs & 0xfffffff) * 10000 + nsecs) % 0x100000000;
  b[i++] = (tl >>> 24) & 0xff;
  b[i++] = (tl >>> 16) & 0xff;
  b[i++] = (tl >>> 8) & 0xff;
  b[i++] = tl & 0xff;

  // `time_mid`
  const tmh = ((msecs / 0x100000000) * 10000) & 0xfffffff;
  b[i++] = (tmh >>> 8) & 0xff;
  b[i++] = tmh & 0xff;

  // `time_high_and_version`
  b[i++] = ((tmh >>> 24) & 0xf) | 0x10; // include version
  b[i++] = (tmh >>> 16) & 0xff;

  // `clock_seq_hi_and_reserved` (Per 4.2.2 - include variant)
  b[i++] = (clockseq >>> 8) | 0x80;

  // `clock_seq_low`
  b[i++] = clockseq & 0xff;

  // `node`
  for (let n = 0; n < 6; ++n) {
    b[i + n] = node[n];
  }

  return b
}

const byteToHex = [];

for (let i = 0; i < 256; ++i) {
  byteToHex.push((i + 0x100).toString(16).substr(1));
}

function v1({ node = [ 0x00, 0x00, 0x00, 0x00, 0x00, 0x00 ], clockseq = 0, msecs = Date.now(), nsecs = 0 } = {}) {
  let i = 0;
  const b = new Array(16)
  
  clockseq = clockseq & 0x3fff;

  // Per 4.1.4 - Convert from unix epoch to Gregorian epoch
  msecs += 12219292800000;

  // `time_low`
  const tl = ((msecs & 0xfffffff) * 10000 + nsecs) % 0x100000000;
  b[i++] = (tl >>> 24) & 0xff;
  b[i++] = (tl >>> 16) & 0xff;
  b[i++] = (tl >>> 8) & 0xff;
  b[i++] = tl & 0xff;

  // `time_mid`
  const tmh = ((msecs / 0x100000000) * 10000) & 0xfffffff;
  b[i++] = (tmh >>> 8) & 0xff;
  b[i++] = tmh & 0xff;

  // `time_high_and_version`
  b[i++] = ((tmh >>> 24) & 0xf) | 0x10; // include version
  b[i++] = (tmh >>> 16) & 0xff;

  // `clock_seq_hi_and_reserved` (Per 4.2.2 - include variant)
  b[i++] = (clockseq >>> 8) | 0x80;

  // `clock_seq_low`
  b[i++] = clockseq & 0xff;

  // `node`
  for (let n = 0; n < 6; ++n) {
    b[i + n] = node[n];
  }
  
  return (
    byteToHex[b[0]] + byteToHex[b[1]] + 
    byteToHex[b[2]] + byteToHex[b[3]] +
    '-' +
    byteToHex[b[4]] + byteToHex[b[5]] +
    '-' +
    byteToHex[b[6]] + byteToHex[b[7]] +
    '-' +
    byteToHex[b[8]] + byteToHex[b[9]] +
    '-' +
    byteToHex[b[10]] + byteToHex[b[11]] + byteToHex[b[12]] + 
    byteToHex[b[13]] + byteToHex[b[14]] + byteToHex[b[15]]
  ).toLowerCase();
}

console.log(v1({ msecs: Date.parse('04 Dec 1995 00:12:00 GMT') })) 
// 5fc18800-2dd0-11cf-8000-000000000000

const byteToHex = [];

for (let i = 0; i < 256; ++i) {
  byteToHex.push((i + 0x100).toString(16).substr(1));
}

const mapHex = (block = []) => block.map(x => byteToHex[x]).join("")

function v1({ node = [ 0x00, 0x00, 0x00, 0x00, 0x00, 0x00 ], clockseq = 0, msecs = Date.now(), nsecs = 0 } = {}) {
  clockseq = clockseq & 0x3fff;
  msecs += 12219292800000; // Per 4.1.4 - Convert from unix epoch to Gregorian epoch
  
  const tl = ((msecs & 0xfffffff) * 10000 + nsecs) % 0x100000000;
  const tmh = ((msecs / 0x100000000) * 10000) & 0xfffffff;
  
  const block1 = [ (tl >>> 24) & 0xff, (tl >>> 16) & 0xff, (tl >>> 8) & 0xff, tl & 0xff ]
  const block2 = [ (tmh >>> 8) & 0xff, tmh & 0xff ]
  const block3 = [ ((tmh >>> 24) & 0xf)| 0x10, (tmh >>> 16) & 0xff ]
  const block4 = [ (clockseq >>> 8) | 0x80, clockseq & 0xff ]
  
  return `${mapHex(block1)}-${mapHex(block2)}-${mapHex(block3)}-${mapHex(block4)}-${mapHex(node)}`.toLowerCase();
}

console.log(v1({ msecs: Date.parse('04 Dec 1995 00:12:00 GMT') })) 
// 5fc18800-2dd0-11cf-8000-000000000000