Isn't the idea of asm.js that if a program is written according to the spec you can generate simpler and so hopefully faster code? That applies whether you're generating bytecode or machine code.

Sure, but you'd have to generate asm.js in the first place. It's compiler target that also happens to map to a small subset of JavaScript, you're unlikely to find writing asm.js by hand useful.

DynJS could also support asm.js in addition to JavaScript, but that has almost nothing to do with JIT-ing JavaScript applications.

Right. I wasn't thinking of this as the _only_ JIT case, but one that could generate faster code by not having to do complex type tracing or inference. Seems like low hanging fruit to detect asm.js and read it directly into a typed AST.

Probably, yes.

Although with invokedynamic, the JVM's object system ends up being remarkably close to that of a dynamic language. This is best seen in JRuby.