test.js

'use strict';

// This class is used for logins
class Login {
  constructor(hash) {
    this.sessions = [];
    this.users = [];
    this.passwords = [];
    Object.keys(hash).map(k => ({k, v: hash[k]})).map(e => {
      this.users = this.users.concat([e.k]);
      this.passwords = this.passwords.concat([e.v]);
    });
  }

  logout(user) {
    for (let i=0; i<this.sessions.length; i++) {
      if(this.sessions[i]===user){
        this.sessions[i] = null;
      }
    }
    this.sessions = this.sessions.filter(session => session !== null);
  }

  // Checks if user exists
  userExists(user) {
    for (let i of this.users) {
      if (i === user) {
        return true;
      }
    }
    return false;
  }

  // Register user
  registerUser(user, password) {
    this.users.push(user);
    this.passwords.push(password);
  }

  removeUser(user) {
    let index = this.users.indexOf(user);
    this.users[index] = null;
    this.passwords[index] = null;
    this.users = this.users.filter(user => user !== null);
    this.passwords = this.passwords.filter(password => password !== null);
  }

  checkPassword(user, password) {
    let index = this.users.indexOf(user);
    let passwordCorrect = this.passwords[index] === password;
    return passwordCorrect;
  }

  updatePassword(user, oldPassword, newPassword) {
    // First we check if the user exists
    if(this.userExists(user)){
      let index = this.users.indexOf(user);
      if (this.passwords[index] === oldPassword) {
        this.passwords[index] = newPassword;
        return true;
      }
    }
    return false;
  }

  login(user, password) {
    let index = this.users.indexOf(user);
    if (this.passwords[index] === password) {
      this.sessions.push(user);
    }
  }

}

let registeredUsers = {
  user1: 'pass1',
  user2: 'pass2',
  user3: 'pass3'
};

let login = new Login(registeredUsers);

login.registerUser('user4', 'pass4');
login.login('user4', 'pass4');
login.updatePassword('user3', 'pass3', 'pass5');
login.login('user3', 'pass5');
login.logout('user4');
login.logout('user3');