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 (

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/ 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.