> Okay, but how about other JavaScript engines? SpiderMonkey uses NaN-boxing, so pointers to objects will sometimes take up less space than in V8. As for hidde

> Okay, but how about other JavaScript engines? SpiderMonkey uses NaN-boxing, so pointers to objects will sometimes take up less space than in V8. As for hidden classes, I'm not sure about how shapes (SpiderMonkey's term for hidden classes) interact with constructors. > And shouldn't stuff like this be in the specs, so that the language becomes more consistent and predictable? That would stifle compiler innovation. Not even the "low-level", "predictable" C and C++ mandate particular implementations, beyond specifying the bare minimum necessary to ensure pointer arithmetic works portably.