asm.js now allows the heap to be resized (by replacing the heap's ArrayBuffer with a newer, bigger ArrayBuffer that was either copied or produced via ES7-proposed ArrayBuffer.transfer [1]). Heap resizing currently has to be enabled in Emscripten (by passing -s ALLOW_MEMORY_GROWTH=1), but may become the default in the future. The main asm.js spec page hasn't been updated yet, but the extension was discussed publicly with comments from Microsoft engineers [2].
That is nice to hear. I don't keep enough track to see that this was being discussed, but it does deal with the only major issue I had with C++ -> asm.js code conversion, particularly for mobile.
[1] https://developer.mozilla.org/en-US/docs/Web/JavaScript/Refe... [2] http://discourse.specifiction.org/t/request-for-comments-swi...