# React to consumer changes

This page discusses how to react to consumer changes within the Kustom Checkout iframe.  Two methods are described: client-side events (using a Javascript API) and server-side callbacks.

## How it’s done

Refer to the following pages for details:

* [Client-side events](/contents/checkout/additional-resources/client-side-events/)
* [Server-side callbacks](/contents/checkout/additional-resources/server-side-callbacks/)