uuid/lib/rng-browser.js

// Unique ID creation requires a high quality random # generator.  In the
// browser this is a little complicated due to unknown quality of Math.random()
// and inconsistent support for the `crypto` API.  We do the best we can via
// feature-detection
var rng;

var crypto = global.crypto || global.msCrypto; // for IE 11
if (crypto && crypto.getRandomValues) {
  // WHATWG crypto RNG - http://wiki.whatwg.org/wiki/Crypto
  var rnds8 = new Uint8Array(16);
  rng = function whatwgRNG() {
    crypto.getRandomValues(rnds8);
    return rnds8;
  };
}

if (!rng) {
  // Math.random()-based (RNG)
  //
  // If all else fails, use Math.random().  It's fast, but is of unspecified
  // quality.
  var  rnds = new Array(16);
  rng = function() {
    for (var i = 0, r; i < 16; i++) {
      if ((i & 0x03) === 0) r = Math.random() * 0x100000000;
      rnds[i] = r >>> ((i & 0x03) << 3) & 0xff;
    }

    return rnds;
  };
}

module.exports = rng;