Example of Back In Stock form with MailChimp checkbox

form

<label>Email me when available</label>
<input type="email" id="notify_email" />
<input type="checkbox" id="notify_opt_in" value="Yes" /> Opt-in in for
email newsletter
<button id="notify_button">Email when available</button>

<script>
  var notificationCallback = function(data) {
    var msg = '';
    if (data.status == 'OK') {
      msg = data.message; // just show the success message
    } else { // it was an error
      for (var k in data.errors) {  // collect all the error messages into a string
        msg += data.errors[k].join();
       }
    }
    alert(msg);
  }

  $('#notify_button').click(function(e) {
    e.preventDefault();
    var email = $('#notify_email').val(),
        productId = {{product.id}},
        variantId = {{product.variants.first.id}}; // rendered by Liquid
        
    var options = {
      accepts_marketing: $('#notify_opt_in').is(':checked')
    };

    BISPopover.create(email, variantId, productId, options).then(notificationCallback);
  })
</script>