But will JavaScript be able to scale? It has come a long way from the days of onMouseOver but it seems like it's going to be hard unless it gets turned into a different language (i.e. Dart).
V8 increases performance by compiling JavaScript to native machine code (x86,[2] ARM,[2] or MIPS[3] CPUs), before executing it, versus executing bytecode or interpreting it. Further performance increases are achieved by employing optimization methods such as inline caching.
I mean the language itself, not the performance of the individual implementations. For example, I can't imagine prototype based OO being used for large scale projects.