The variance in JIT optimizations will be much wider than the variance in compiling C code to NACL compliant x86 code. In one case, you have varying implementat

The variance in JIT optimizations will be much wider than the variance in compiling C code to NACL compliant x86 code. In one case, you have varying implementations of a runtime compiler, in the other, you have a single compiler known to the game-dev ahead of time, what varies in the sandbox hit. Yes, pepper is an abstraction, but you get concurrency primitives which is lower level than asm.js. The reality is, neither asm.js nor NaCl are going to succeed in getting the gamedev community onto the web platform. The two most popular platforms, iOS and Android, have native SDKs, and so do the consoles and desktops, so any developer who wants to maximize revenue is going to want to target those. The additional headache of a browser port onto a heavily fragmented platform with unpredictable performance, and an audience that has shown little appetite for paying for web apps pretty much guarantee that this whole asm.js vs NaCL debate is moot. Developers just don't care about runtime portability as far as games are concerned. They will do the work to do a source port for optimal performance if the market is there. Does Electronic Arts or Valve care about getting Battlefield 4 or Portal 2 running in the browser in a portable way? I highly doubt it.