Block page - please wait

Block page to prevent (mini) DOS.

HTML

First part show an overlay, which is by default hidden (display:none).

The script, disables the button, changes the text, shows the overlay, wait 800 ms and then submits.

<!-- This is the busy overlay, show when Startig quiz... -->
<div class="modal-overlay" id="modalOverlay">
    <div class="modal-dialog">
        <div class="loader"></div>
        <p>Please wait... </p>
    </div>
</div>

....

<button type="button" id="submitButton" class=".....">Start</button>

<script>
    document.getElementById('submitButton').addEventListener('click', function () {
        this.disabled = true;
        this.innerText = 'Starting...';
        document.getElementById('modalOverlay').style.display = 'block';
        setTimeout(function () {
            document.getElementById('form').submit();
        }, 800);
    });
</script>

CSS

.modal-overlay {
    position: fixed;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    background: rgba(0, 0, 0, 0.6);
    display: flex;
    justify-content: center;
    align-items: center;
    z-index: 1000;
    display: none;
}

.modal-dialog {
    position: fixed;
    top: 35%;
    left: 40%;
    background: #fff;
    border-radius: 5px;
    padding: 20px;
    text-align: center;
    box-shadow: 0px 0px 10px rgba(0, 0, 0, 0.5);
}

.loader {
    border: 4px solid #f3f3f3;
    border-top: 4px solid #3498db;
    border-radius: 50%;
    width: 40px;
    height: 40px;
    animation: spin 2s linear infinite;
    margin: 0 auto;
    margin-bottom: 10px;
}

@keyframes spin {
    0% {
        transform: rotate(0deg);
    }
    100% {
        transform: rotate(360deg);
    }
}