I tinkered with https://extism.org and basically the use case is that they suggest, namely you can extend software in another programming language but without having to setup a container or VMs on the client. They "just" run the code in the browser and it can be JavaScript, sure, but can also be Python, Go, whatever.

It's quite specific though as I'm working on support programming in the browser.

If you are not deep into letting a very specific kind of user extend, it's probably overkill.

Even then it's a very VERY niche thing because it has to be simultaneously :

- someone who is opinionated about a programming language (either because they know too much, i.e. expert, or not enough, i.e beginner)

- is dedicated enough to want to try to build something on top of an existing system

- does not want to bother with solutions you mentioned