password.js

const PASSWORD_CHARACTERS = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ'
                          + 'abcdefghijklmnopqrstuvwxyz'
                          + '01234567890'
                          + '!#$%&()*+,-./:;<=>?@[]^_`{|}~\/"\' ';

function generateRandomPassword(passwordLength=16) {
  // if crypto not defined, bail
  if (!window.crypto) {
    throw new Error('The "crypto" library is not available');
  }

  // can't be larger than 1024 as not to exhaust the random number generator
  if (length < 1 || length > 1024) {
    throw new Error('Passwords must be between 1 and 1024 characters');
  }

  let randomValues = new Uint32Array(passwordLength),
      password = "",
      totalPasswordCharacters = PASSWORD_CHARACTERS.length;

  window.crypto.getRandomValues(randomValues);

  randomValues.forEach((val) => {
    password += PASSWORD_CHARACTERS[val % (totalPasswordCharacters - 1)];
  });

  return password;
}