Remove a Shopify cart attribute

remove.liquid

{% if cart.attributes.yourCartAttribute %}
  <script>
    $.ajax({
      type: 'POST',
      url: '/cart/update.js',
      data: 'attributes[yourCartAttribute]=',
      dataType: 'json'
    });
  </script>
{% endif %}

Alternatively (and equally undocumented!), you could use the Shopify API directly.

{% if cart.attributes.yourCartAttribute %}
  <script>
    Shopify.updateCartAttributes([{
      key: 'yourCartAttribute',
      value: ''
    }], function(onError) {});
  </script>
{% endif %}

Provide null as the value wherever you normally send the request (e.g. XHR, fetch, et al), and Shopify will remove the key from its attributes hash.

In the original example, you probably want to remove the dataType param, since json isn't a valid MIME type and the payload isn't JSON (obj[key]=value is form urlencoded).

@alpriest @emcmanus by setting the value to null, it doesn't remove the key for me from the order. It just sets the key's value to null. Anyway to actually remove the entire note attribute via the API?