var pw = window.crypto.getRandomValues(new Uint8Array(16));
window.crypto.subtle.importKey("raw", pw, "PBKDF2", false, ["deriveBits"]).then(key => {
  console.log(key);
  var st = window.crypto.getRandomValues(new Uint8Array(16));
  const keySizeBits = 2048;
  // const keySizeBits = 2056; // this breaks
  return window.crypto.subtle.deriveBits({ name: "PBKDF2", salt: st, iterations: 10000, hash: "SHA-256" }, key, keySizeBits);
}).then(bits => {
  console.log(bits);
}).catch(err => {
  console.error(err);
});