uuid_format.js

const buf = Buffer.allocUnsafe(16);

function f1(buf) {
  return (
    buf.slice(0, 4).toString("hex") +
    "-" +
    buf.slice(4, 6).toString("hex") +
    "-" +
    buf.slice(6, 8).toString("hex") +
    "-" +
    buf.slice(8, 10).toString("hex") +
    "-" +
    buf.slice(10, 16).toString("hex")
  );
}

function f2(buf) {
  return [
    buf.slice(0, 4).toString("hex"),
    buf.slice(4, 6).toString("hex"),
    buf.slice(6, 8).toString("hex"),
    buf.slice(8, 10).toString("hex"),
    buf.slice(10, 16).toString("hex"),
  ].join("-");
}

function f3(buf) {
  const sl = buf.toString("hex");
  return [
    sl.slice(0, 8),
    sl.slice(8, 12),
    sl.slice(12, 16),
    sl.slice(16, 20),
    sl.slice(20, 32),
  ].join("-");
}

function f4(buf) {
  const sl = buf.toString("hex");
  return (
    sl.slice(0, 8) +
    "-" +
    sl.slice(8, 12) +
    "-" +
    sl.slice(12, 16) +
    "-" +
    sl.slice(16, 20) +
    "-" +
    sl.slice(20, 32)
  );
}

function f5(buf) {
  const sl = buf.toString("hex");
  return sl;
}

console.log(f1(buf));
console.log(f2(buf));
console.log(f3(buf));
console.log(f4(buf));
console.log(f5(buf));

console.time("f1");
for (i = 0; i < 1000000; i++) {
  f1(buf);
}
console.timeEnd("f1");

console.time("f2");
for (i = 0; i < 1000000; i++) {
  f2(buf);
}
console.timeEnd("f2");

console.time("f3");
for (i = 0; i < 1000000; i++) {
  f3(buf);
}
console.timeEnd("f3");

console.time("f4");
for (i = 0; i < 1000000; i++) {
  f4(buf);
}
console.timeEnd("f4");

console.time("f5");
for (i = 0; i < 1000000; i++) {
  f5(buf);
}
console.timeEnd("f5");

nodejs 10 output:

00000000-0000-0000-0000-000000000000
00000000-0000-0000-0000-000000000000
00000000-0000-0000-0000-000000000000
00000000-0000-0000-0000-000000000000
00000000000000000000000000000000
f1: 1060.335ms
f2: 1219.683ms
f3: 408.617ms
f4: 246.338ms
f5: 149.422ms