(This grew out of a conversation Allen and I had yesterday -- great to see it developed.)
One thing to make clear: > ES5~EAS6: The construct has identical syntax and static semantics in both > ES5 and ES6, but differing semantics. For example, accessing a formal > parameter after an assignment to the corresponding element of the function's > arguments object. This is something we propose to do with completion reform, and also until this year for typeof null. It's clear we can't get away with changing typeof null == "null". Even with full opt-in, it's a runtime migration hazard (one of the five fingers of fate). I withdraw it -- I'm the one who proposed it in lieu of an Object.isObject predicate -- but I do not think we should add Object.isObject either. Rather, we need to rethink reflection on types in light of not only null vs. object, but value types/proxies. I'd rather not rush that. In the mean time, and for lo these 16 years (heading toward 17!), developers have coped and can continue to do so with typeof x == "object" && x === null or simpler (!x, x == null, other context-specialized combinations). In general, the latest "new syntax is its own opt-in" thinking, with Allen's state machine approach, means our five fingers of fate have to be small enough that we can get away with them. At least Mark and I believe completion reform (making the completion value depend on a statically decidable expression-statement) is the only such finger we can get away with folding right now. > If you want to explicitly force ES6 processing put a: > let ES6; Or (no quotes) use strict; I think we want this pragma supported, not only the string-literal expression-statement "directive". > at the top of the source file. > > If you want to explicitly force ES5 processing put a: > with (5); > at the top of the source file That will potentially deoptimize the top level for some engines, but maybe it doesn't matter. I don't expect it to catch on ;-). /be _______________________________________________ es-discuss mailing list es-discuss@mozilla.org https://mail.mozilla.org/listinfo/es-discuss
