index.js

var database = firebase.database();

$(document).ready(function () {
  $(".sign-up-button").click(signUpClick);
  $(".sign-in-button").click(signInClick);
});

function signUpClick(event) {
  event.preventDefault();
  var email = $(".sign-email").val();
  var password = $(".sign-password").val();
  createUser(email, password);
}

function createUser(email, password) {
  firebase.auth().createUserWithEmailAndPassword(email, password)
    .then(function (response) {
      var userId = response.user.uid;
      database.ref("users/" + userId).set({
        email: email
        
      });
      alert("Cadastro concluido com sucesso !!!\n " + email);
      window.location = "main.html?id=" + userId;
      
    })
    .catch(function(error) {
      handleError(error);
    });
}

function signInClick(event) {
  event.preventDefault();
  var email = $(".sign-email").val();
  var password = $(".sign-password").val();
  signInUser(email, password);
}

function signInUser(email, password) {
  firebase.auth().signInWithEmailAndPassword(email, password)
    .then(function(response) {
      var userId = response.user.uid;
      redirectToTasks(userId);
    })
    .catch(function(error) {
      handleError(error)
    });
}

function handleError(error) {
  var errorMessage = error.message;
  alert(errorMessage);
}

function redirectToTasks(userId) {
  window.location = "main.html?id=" + userId;
}