function pwm(length) {
  var characters = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz23456789'.split('');
  var password = '';
  for (i = 0; i < length; i++) {
    password += characters[Math.floor(Math.random() * characters.length)];
  }
  return password;
}