Generate Minecraft OfflinePlayer UUID

playername_to_UUID.js

const { exit } = require("process");

const createHash = require("crypto").createHash;

// Reads from cli
if (process.argv.length < 3) {
  process.stdout.write("\n");
  exit(1);
}

const hash = createHash("md5"); // v3
hash.once("readable", () => {
  const data = hash.read();
  const uuid = [...data];
  // https://www.rfc-editor.org/rfc/rfc4122#section-4.3
  uuid[6] = (data[6] & 0x0f) | 0x30; // v3
  uuid[8] = (data[8] & 0x3f) | 0x80;
  process.stdout.write(splittedUUID(toHexString(uuid)));
});

function toHexString(byteArray) {
  return byteArray
    .map((byte) => ("0" + (byte & 0xff).toString(16)).slice(-2))
    .join("");
}

function splittedUUID(uuid) {
  return [
    uuid.substring(0, 8),
    uuid.substring(8, 12),
    uuid.substring(12, 16),
    uuid.substring(16, 20),
    uuid.substring(20, 32)
  ].join("-");
}

hash.write("OfflinePlayer:" + process.argv[2]);
hash.end();

Here you go @siraly1636

Thank you so much. @ErnestoRB I have already successfully integrated it into my website.