password.js

function getRandomBytes(length) {
  var bytes = new Uint8Array(length);
  window.crypto.getRandomValues(bytes);
  return bytes;
}

function generatePassword(length) {
  // To avoid modulo bias, alphabet length must conform to 256 % length == 0, e.g. 64.
  var alphabet = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789_@'.split('');
  var bytes = getRandomBytes(length);
  var result = "", i;
  for (i = 0; i < length; i++) {
    result += alphabet[bytes[i] % alphabet.length];
  }
  return result;
}