hallotoyou.html

<!DOCTYPE html>
<html lang="en">

<Head>
    <title>Hallo to you</title>
</Head>

<body>
    <form>
        <input autofocus id="name" placeholder="Name" type="text">
        <input type="submit">
    </form>
    <script>

        document.querySelector('form').addEventListener('submit', function (e) {
            let name = document.querySelector('#name').value;
            alert('hallo, ' + name);
            e.preventDefault()
        });
    </script>


</body>

</html>