> The special interpreter is what I've inferred from pcwalton's comment of their being an optimized interpreter for it in Firefox. If its the same JS VM how can

> The special interpreter is what I've inferred from pcwalton's comment of their being an optimized interpreter for it in Firefox. If its the same JS VM how can anything fail the type checker (e.g. forgetting a '+' or '|') cause it to run much slower? The type checker either succeeds or fails to type check. If it succeeds, we know all the types and send those with the code to IonMonkey (just like normal code, except with the types). Otherwise, we run it normally, and eventually it will also get sent to IonMonkey (with types inferred at runtime). So failing to type check can make a difference in performance. It should not be large, and if you look on awfy, on most benchmarks it in fact is not (it is larger on large benchmarks though, which need more attention). > I've got the latest version of Chrome and it always crashes for me Yes, this was fixed by the Chrome devs, but not yet in a stable release. Please try the Chrome dev build for example, and you'll see it runs very well there. In just a matter of weeks that will be true in stable Chrome as well.