With or without "use asm", as hackcasual mentioned, we don't have the control we need, like one might have on some platforms in C. Some of the articles we reference in the top section of the blog post mention this about Javascript and are great reads. We selected these particular primitives because the authors mention avoiding timing attacks as a key feature of their C. We believe that aspect to their libraries is still fantastic even after being compiled with Emscripten, but you're certainly right in saying that JIT'ing and Asm.js complicate things.