v4 UUID generation using crypto.getRandomValues

uuid.js

export default function () {
  // returns an RFC 4122 compliant UUID using the crypto API
  // Based on https://gist.github.com/bentranter/ed524091170137a72c1d54d641493c1f with
  // a fix to have padding for numbers < 16

  // get sixteen unsigned 8 bit random values
  let u = window.crypto.getRandomValues(new Uint8Array(16));

  // set the version bit to v4
  u[6] = (u[6] & 0x0f) | 0x40;

  // set the variant bit to "don't care" (yes, the RFC
  // calls it that)
  u[8] = (u[8] & 0xbf) | 0x80;

  // hex encode them and add the dashes
  let uid = '';

  for (let i = 0; i < u.length; i++) {
    if (u[i] < 16) {
      uid += '0';
    }
    uid += u[i].toString(16);

    if ([3, 5, 7, 9].indexOf(i) > -1) {
      // includes() is not supported in IE
      uid += '-';
    }
  }

  return uid;
}