ajax-register.php

<?php
    // allow the Config
    define('__CONFIG__', true);
    // require the config
    require_once '../inc/config.php';

if($_SERVER['REQUEST_METHOD']=='POST' or 1==1){

    // Always return JSON Format
    //header('Content-Type : application/json');
    $return = [];

    $email = Filter::String($_POST['email']);

    //make sure the user does not exist
    $findUser = $con->prepare('SELECT user_id FROM users WHERE email= LOWER(:email) LIMIT 1');
    $findUser->bindParam(':email' ,$email, PDO::PARAM_STR);
    $findUser->execute();

    if(findUser -> rowCount == 1){
        // user exist
        $return['error'] = 'the email address already registered in our database.';

        $return['is_logged_in'] = false;
    }else{
        // user can be register

        $password = password_hash($_POST['password'], PASSWORD_DEFAULT);

        $addUser = $con->prepare('INSERT INTO users(LOWER(email), password) VALUES(LOWER(:email) , :password)');
        $addUser->bindParam(':email' , $email, PDO::PARAM_STR);
        $addUser->bindParam(':password' , $password, PDO::PARAM_STR);
        $addUser->execute();

        $user_id = $con -> lastInserId();

        $_SESSION['user_id'] = int() $user_id;

        $return['redirect'] = '/dashboard.php?message=welcome';
        $return['is_logged_in'] = true;
    }

    echo json_encode($return, JSON_PRETTY_PRINT); exit;
    }else{
        exit('invalid URL');
    }

 ?>