OK. So we have reached "Peak JavaScript" then. If people write JS code without triggering shape changes then the JIT should be able to produce code that can match a JVM? If there was something that I could do as a developer that could help the JIT I would do it.
Would ES6 classes not make the creation of shapes a lot easier? From what I understand it takes time to figure out shapes/hidden-classes. Well I'm marking this object as a class, does that help? It would be interesting if engines provided feedback on when we developers break the optimistic optimizations. On Sat, Jul 13, 2013 at 9:43 AM, David Bruant <[email protected]> wrote: > Le 13/07/2013 10:21, Brian Di Palma a écrit : > >> I was just wondering >> if the 'const' keyword would help give JS another small performance >> boost. > > Unlikely. Const can be almost statically inferred (no assignment to a given > variable). The "almost" refers to cases where eval happens. Worst case, if > there is no assignment, a variable can be optimistically optimized as const. > If the value is changed via eval, then de-optimize (but in practice, eval is > rare, so the optimistic optimization will be worth it) > > >> As Andreas points out the major issue is that JS is highly dynamic, >> this can be very useful sometimes but for most code it's not required. >> Maybe if you mark everything as const or freeze/seal classes then >> maybe JS engines will optimize for that code. > > JS engines already optimistically optimize assuming code remains stable (for > objects, V8 has "hidden classes", SpiderMonkey has the equivalent "shape" > feature) and deoptimizes when the dynamic features are being used. > > It might be one of the reason why maps are better at being maps than objects > (since objects seem to have been optimized for cases where they are stable) > > David _______________________________________________ es-discuss mailing list [email protected] https://mail.mozilla.org/listinfo/es-discuss
