(If I understand correctly) I'd write transcompiler (based on Narcissus or whatever) to instrument your code with statements at the top of each function to chec

(If I understand correctly) I'd write transcompiler (based on Narcissus or whatever) to instrument your code with statements at the top of each function to check and record the types. I think a basic version of this could be built in a day. Advantages of instrumenting the code: 1. No mucking around in V8 internals. 2. Works on any JavaScript engine.