I actually find it very impressive that they have a quite well working tracing JIT. For Firefox we had TraceMonkey, but the code was hard to maintain and hacked

I actually find it very impressive that they have a quite well working tracing JIT. For Firefox we had TraceMonkey, but the code was hard to maintain and hacked into the infrastructure. And it turned out that most stuff doesn't trace very well in the real world. (not SunSpider, argg!) I haven't looked very recently but I guess the pypy frontend for JavaScript is still not actively maintained? I think I remember seeing some thesis about that recently. Best of luck to them in the coming years!