I would rather say that article says that the trace jit they build is only faster for tight, non-branchy code. I would say that the generall JS programmen has this property but Mike Pall has showed that in the end trace-jit are better. He wrote LuaJit 1 witch is a method jit and LuaJit 2 witch is a trace-jit and his conclution with luajit one was that he hit a performance wall.