Many, if not most, of the people working on advanced JavaScript VMs come from a Java background. I would say JS VMs are orders of magnitude more sophisticated i

Many, if not most, of the people working on advanced JavaScript VMs come from a Java background. I would say JS VMs are orders of magnitude more sophisticated in the type of behavioral profiling they do in order to recover types, understand object shapes, and shortcut prototype lookups. While HotSpot and Azul (a progeny of HotSpot) are highly tuned, a lot more investment has gone into bread-and-butter JIT and GC work, whereas JS runtimes have to have a very advanced object model and type profiling infrastructure.