Have you been following Meta's work on Static Hermes? It's one of two efforts I'm aware of* to define a subset of JavaScript with different runtime semantics, b

Have you been following Meta's work on Static Hermes? It's one of two efforts I'm aware of* to define a subset of JavaScript with different runtime semantics, by putting limitations on dynamic behavior. Their primary goal is performance, but correctness benefits also seem likely, and they share your idea that being intended for embedding in a particular application lets you get away with breaking compatibility in ways that you couldn't in a browser. And if their thing ships, and you want to reduce fragmentation, then maybe you want your "sane subset" to match theirs. * The other being Google's Closure Compiler, which probably isn't relevant to you as it assumes that its output has to run on existing engines in browsers.