It sounds like a good idea, but every time I've seen this implemented it's been as a simple whitelist lookup against user agent. This has two problems. First, user agent is... unreliable. Second, people that use less common systems are erroneously told the page won't work. (I've lost count of the number of times a website has told me that my operating system isn't supported yet the page works fine. What does my os have to do with a web page anyway?)

I have been developing my app for years and I am trying to be as OS-independent and browser-independent as possible.

To detect the availability of the feature, I am chechking if the constructor is available, or if some property of an object is available. I never try to whitelist or blacklist any specific OS or a browser. I have never made any part of the code behave differently for some OS or some browser. But I have reported dozens of bugs to browser developers, most of them were fixed.

Photopea runs quite well on phones and tablets. If your microwave oven passes WillItWork, it will work on it too :)

Very cool. Cheers.

Photopea appears to do it properly with feature testing (no UA checks): https://www.photopea.com/willitwork/test.js

FYI, Modernizr is a fantastic library for browser feature testing. You can just "add to cart" the tests you want to perform. No hand rolling necessary: https://modernizr.com/