I wrote a little CORS tester tool to make testing urls for CORS easier. Mostly I was interested in experimenting with Cloudflare workers more. The entire site is deployed as a Cloudflare worker and served by a single js file. It worked real nicely for a small site. For a larger project, it would likely benefit from a bit of a framework for separating out the views (HTML). The 30-40ms response times from anywhere are real impressive.
Link: CORS Tester.
A tiny tool for checking if your CORS headers are setup correctly.