Loading external Scripts with JS based on current Subdomain

I would like to load those external scripts below with JS based on the current subdomain someone is on. Could you help me writing the function doing this?

order.test.de

<script src="https://test.com/banner.js" data-key="820ed7d9-95be-460f-be32-cf569f640fb4"></script>

order.test.ch

<script src="https://test.com/banner.js" data-key="6e4718c5-df40-4f94-83cc-16e8b105e6b9"></script>

order.test.com

<script src="https://test.com/banner.js" data-key="5e593e1d-dc8c-482f-a0b8-b5a82b3cad04"></script>