What I have done is added that if you are using a bundler you must set it to use es2020. I have put this under its own section for clarity. Maybe if we could add more troubleshooting problems like this we could make a FAQ, but because its only one problem the user may encounter, I've put it in its own section.

Thanks!

In general, I'd like to make sure that js.cubing.net is the canonical place for info. https://js.cubing.net/cubing/#javascript already mentions:

If you are having trouble, make sure your tool is compatible with ES2020 syntax. We recommend using esbuild or tools based on esbuild, and you may find this project template a helpful start.

Do you think you could make this a more concise reference in an existing section?

Also, in the past I would have avoided a reference to Vite, but given all the compatibility issues with Parcel it looks like the best "batteries included" bundler for now. I think it would be alright to have a slightly expanded section with Vite as an example, although I'd like to keep it on the website and as concise as possible.

Would you be able to update this, taking all that into account?
(It's alright if not, I can also update it myself when I get around to it.)

Would you be able to update this, taking all that into account?

Yes, I'll update it as soon as possible.

Okay, so now I've moved the section to docs/cubing/index.html, and I've kept the details on Vite as minimal as possible.

So, I spent some time this week trying to get Vite to have full compatibility with es2020, and did not succeed.

From vitejs/vite#9062 it sounds like we won't work in Vite out of the box until Vite 4 — and Vite 3 is barely released. I wanted to be able to recommend Vite as a bundler in our docs, but I have to give up on that for now, and I'm reluctant to mention them all if we have such reservations. :-/

I'd like to keep thinking about this, apologies for the delay.