Generates a RFC 4122 version 4 UUID using cryptographically secure random numbers.

uuidv4.js

/**
* uuidv4.js
*
* Generates a RFC 4122 version 4 UUID using cryptographically secure random numbers.
* Falls back to Node.js crypto if not in a browser.
* Throws if no cryptographically secure PRNG is available.
*
* Vibe coding using GitHub CoPilot and ChatGPT.
*
* @returns {string} The generated UUID string in the standard 8-4-4-4-12 format.
*/
(function (global, factory) {
  if (typeof module !== 'undefined' && typeof module.exports !== 'undefined') {
    // CommonJS (Node.js)
    module.exports = factory(require('crypto'));
  } else if (typeof define === 'function' && define.amd) {
    // AMD (if needed)
    define(['crypto'], factory);
  } else {
    // Browser global
    global.uuidv4 = factory(global.crypto);
  }
})(typeof globalThis !== 'undefined' ? globalThis : this, function (cryptoSource) {
  function getSecureRandomValues(arr) {
    if (cryptoSource && typeof cryptoSource.getRandomValues === 'function') {
      return cryptoSource.getRandomValues(arr); // Browser
    } else if (cryptoSource && typeof cryptoSource.randomFillSync === 'function') {
      return cryptoSource.randomFillSync(arr); // Node.js
    } else {
      throw new Error('No cryptographically secure random number generator available.');
    }
  }

  function uuidv4() {
    const bytes = getSecureRandomValues(new Uint8Array(16));

    // Set version and variant bits
    bytes[6] = (bytes[6] & 0x0f) | 0x40; // Version 4
    bytes[8] = (bytes[8] & 0x3f) | 0x80; // Variant 10xx

    const hex = Array.from(bytes, b => b.toString(16).padStart(2, '0'));
    return (
      `${hex.slice(0, 4).join('')}-` +
      `${hex.slice(4, 6).join('')}-` +
      `${hex.slice(6, 8).join('')}-` +
      `${hex.slice(8, 10).join('')}-` +
      `${hex.slice(10).join('')}`
    );
  }

  return uuidv4;
});