[azakai]

Very correct, but a side note: asm.js might not be useful or necessary for this. asm.js makes more of a difference in large, hard to optimize codebases, and less in small amounts of code, because JS engines have been optimizing small amounts of code extremely well for a while now (using TraceMonkey, CrankShaft, DFG, IonMonkey, etc.).

Also, asm.js code is structured in a way that makes it obvious the code will not change over time (it's in a closure, where functions cannot be modified), again, in order to make optimizing large projects easier. When JITing however you do want to add new code all the time.

But this could work great without generating asm.js code. The VM itself is C code that can be compiled wholesale into asm.js (when the Lua VM was compiled that way it was quite fast, about 50% of native speed), and it would then JIT at runtime normal JS and call into that.

[slacka]

"asm.js might not be useful or necessary for this" So for situations like this, would Duetto's approach of mapping C++ objects/functions to native JavaScript objects/functions be better? If so, is this a feature that could be added in the future to Emscripten or are the designs mutually exclusive?

[azakai]

Both the emscripten/mandreel and duetto approaches map functions to functions. The difference is that duetto maps objects to objects as well.

AFAIK the duetto approach brings no benefits in this case.