GA - form - submission

// Fire this dataLayer event when a successful submission of the Contact us form occurs. The event should fire only for successful submissions. The event shouldn't fire again if the user reloads or revisits the thank-you page.

<script>
window.dataLayer = window.dataLayer || [];
window.dataLayer.push({
 'event': 'form_submission',
 'form_name': 'Contact us'
 });
</script>