I'm not sure about JS being necessarily that slow... The browser engines have done tremendous work in the last decade to make it very performant. It approaches java in some regards... It would be interesting to even see applications where this difference would be noticeable, let alone application examples where there would need to be so much complex logic in scripting itself, and also so much sheer computation requirements where this would ever make any difference...

Also then, if this would be the selling point of ChaiScript, I would want to see some benchmarks (I have a hard time believing it will outperform lua with the built-in JIT or one of the faster JS engines with optimizations (it's not like performance is a novel desire in embeddable scripting languages, tons of manhours have been put into them already))... The website doesn't seem to have any such benchmarks.