Form submission event

README.md

After form submission (Vendor)

<form id="sweepsForm">
  <!-- form fields here -->
</form>

<script>
  const form = document.querySelector('#sweepsForm');

  form.addEventListener('submit', (event) => {
    window.parent.postMessage({
      name: 'sweepsFormSuccess'
    }, '*')
  });    
</script>

On microsite (Colle McVoy)

<script>
  window.addEventListener('message', (event) => {
    if (event.data.name === 'sweepsFormSuccess') {
      // show sweeps giveaway UI
    }
  });
</script>