youre welcome.

savePasswordAssignmentSolution.js

const crypto = require("crypto");

class Db {
  constructor(users={}) {
    this.users = users;
  }

  // Expects passwordPayload to be a string of the form 'salt$passwordHash'
  // Where the '$' is used as a separator.
  storeUser(username, passwordPayload) {
    this.users[username] = passwordPayload;
  }

  getUserPassword(username) {
    let hash = this.users[username];
    return {
      salt: hash.substr(0, hash.indexOf('$')),
      passwordHash: hash.substr(hash.indexOf('$') + 1)
    };
  }
}
const db = new Db();


// STUDENT CODE STARTS HERE ------------

const hashPassword = (password, salt) => {
  const passwordHash = crypto.pbkdf2Sync(password, salt, 70451, 64, 'sha256');
  return passwordHash.toString('hex');
};

const saveUser = (username, password) => {
  const salt = crypto.randomBytes(64).toString('hex');
  const passwordHash = hashPassword(password, salt);
  const payload = `${salt}$${passwordHash}`;
  db.storeUser(username, payload);
};

// Return true if authenticated, false otherwise.
const isUserAuthenticated = (username, password) => {
  let payload;
  try {
    payload = db.getUserPassword(username);
  } catch (error) {
    if (!(error instanceof TypeError)) throw error;

    // insert work
    hashPassword('notARealPassword', 'mySaltIsbetterThanMyPepper');

    return false;
  }

  const { salt, passwordHash } = payload;

  return comparePasswords(password, salt, passwordHash);
};

// returns true if passwords match, otherwise false.
const comparePasswords = (plaintextPassword, salt, passwordHashFromDb) => {
  return hashPassword(plaintextPassword, salt) === passwordHashFromDb;
};

// STUDENT CODE ENDS HERE ------------

saveUser('[email protected]', '123456qwerty');

console.time('1')
console.log(isUserAuthenticated('[email protected]', 'HelloWorld!'))            // false
console.timeEnd('1')
console.time('2')
console.log(isUserAuthenticated('[email protected]', 'HelloWorld!'))            // false
console.timeEnd('2')
console.time('3')
console.log(isUserAuthenticated('[email protected]', 'HelloWorld!'))   // false
console.timeEnd('3')
console.time('4')
console.log(isUserAuthenticated('[email protected]', '123456qwerty'))            // true
console.timeEnd('4')