The "obvious" way. (The same runtime that you're planning to use for the JS you mentioned in your original comment. <https://news.ycombinator.com/item?id=28349504>)

And do the generation on the client side?

If by "client side" you mean in the web browser of you, the author of a new piece of content, then yes—a site that is "capable of generating itself". (If you mean templates that are evaluated in the browser of every site visitor every time they refresh the page, then no.)

Ah, yeah, finally got your "capable of generating itself" idea. Pretty cool, interesting to experiment on it. I guess it would be something like a site that downloads itself also.