gfodor

Worth noting: the demo is a WASM-compiled instance of this engine. I'm not sure, but I think this might be the first example of a fully featured, potentially production-ready, JS VM sandbox running in the browser. (We're looking into safe ways to enable third party scripting of our own application, and such a sandbox would be a very nice tool to have in hand.)

azakai
Definitely not the first JS VM compiled to the browser. Aside from JSC as another comment mentioned, there was also js.js which is SpiderMonkey compiled to JS (around 2012!),

https://github.com/jterrace/js.js/

This shouldn't be surprising - many VMs have been compiled to the Web, like Lua, Python (both CPython and PyPy!), etc., and JS is just another VM.