login.js

class User {
  constructor(username, password) {
    this.username = username;
    this.password = password;
    this.users = [
      { username: 'grupocodenome', password: 'a123' },
      { username: 'thiagocunha', password: '321' },
      { username: 'thalita', password: 'qwe' },
      { username: 'caroline', password: 'ewq' },
      { username: 'luciana', password: 'asd' },
    ];
  }

  login(user) {
    const foundUser = this.users.filter(registeredUser =>
      registeredUser.username === user.username && registeredUser.password === user.password)[0];
    if (foundUser) {
      return {
        message: 'Login is successful',
        status: true,
      };
    }
    return {
      message: 'Invalid username or password',
      status: true,
    };
  }
}

function signin() {
  const username = document.getElementById('inputUsername').value;
  const password = document.getElementById('inputPassword').value;
  const message = document.getElementById('message');

  const user = new User(username, password);
  const result = user.login(user);

  if (result.status === true) {
    message.className = 'alert alert-success';
    message.innerText = result.message.toString();
  } else {
    message.className = 'alert alert-danger';
    message.innerText = result.message.toString();
  }
}