I am working on a project based on asm.js technology. From my experience very limited and simple asm.js code might be compatible with "all non asm.js browsers". In particular I found IE9 wouldn't work with some compiled code. IE10 so far so good (but slow of course.)
Yes, you are right, but I found back then that not all code can be compiled without these arrays. Can't remember why right now tho. So there are certainly issues with browsers not supporting typed arrays.
Yes, it is tricky to compile without typed arrays. It means we need to disable LLVM optimizations, and also a lot more undefined behavior in C will fail (anything that assumes memory aliasing).
With a little effort stuff can be ported, I ported CPython that way. But typed arrays is far better.
