You're conflating a few things here. V8 and Spidermonkey aren't the only interpreters out there. There are a number of them explicitly designed to be small, eas

You're conflating a few things here. V8 and Spidermonkey aren't the only interpreters out there. There are a number of them explicitly designed to be small, easy to compile and to embed, such MuJS, Fabrice Bellard's QuickJS, and more still. I can't speak to their FFI interfaces, but you can't judge JS's ability to call C functions based off that of Node/V8. I'm not sure how FFI runs against its execution model given JS is generally used as an embedded language, necessitating foreign function calls.