Author here. I have a JavaScript port of my automated test suite (https://github.com/a-e-k/canvas_ity/blob/main/test/test.html) that I used to compare my library against browser <canvas> implementations. I was surprised by all of the browser quirks that I found!

But compiling to WASM and running side-by-side on that page is definitely something that I've thought about to make the comparison easier. (For now, I just have my test suite write out PNGs and compare them in an image viewer split-screen with the browser.)