On Jan 16, 2013, at 11:54 AM, Domenic Denicola <[email protected]> wrote:
> Coincidentally, I compiled a list of interesting cases a few days ago, for > both const and let. They were meant to be used in kangax's ES6 compatibility > table: > > https://github.com/kangax/es5-compat-table/issues/58 > > In short: > > const x; // SyntaxError > let x; let x; // SyntaxError > const x = 5; const x = 5; // SyntaxError > x; const x = 5; // ReferenceError > x; let x; // ReferenceError > const x = 2; { x; const x = 5; } // ReferenceError > let x; { x; let x; } // ReferenceError > > plus a test of fresh per-loop iteration for let > > Corrections welcome, and kudos to Brandon Benvie on pointing me to the fact > that those last four should be ReferenceErrors. I'm not too interested in what the spec says these should/should not be. I'm interested in what _shipping_ browser engines do. Presumably IE throws on all of them, but we need a nice table for const which is "supported" by multiple engines to show the differences in behaviour so that we can determine the best intersection. --Oliver > > ________________________________________ > From: [email protected] [[email protected]] on > behalf of Oliver Hunt [[email protected]] > Sent: Wednesday, January 16, 2013 14:40 > To: Brendan Eich > Cc: Mark S. Miller; Mark Miller; [email protected] > Subject: Re: excluding features from sloppy mode > > Even 10? If that's the case anything using const is inherently tied to > jsc,v8,moz,opera behaviour. > > Presumably the strictest of those _works_, but maybe i'm wrong? > > We should probably just enumerate all the differences and see which can be > coalesced and which make "sense" in sloppy mode. > > Obvious cases i can think of: > > -- > const x; > -- > var x; > const x; > x = 5; > -- > const x; > var x; > x = 5; > -- > const x =4; > var x = 5; > log(x) > -- > if (..) > const x = .... > else > const x = .... > -- > > That's it for now. Maybe block scoping const will work in sloppy mode? is > for (const x = ...) valid? > > --Oliver > > > > On Jan 16, 2013, at 11:31 AM, Brendan Eich <[email protected]> wrote: > >> There's no const in IE, so we are pretty sure we can take the hit of >> breaking "Mozilla" (non-IE branches, also WebKit, maybe Opera) code that >> uses const. >> >> /be >> >> Brandon Benvie wrote: >>> The incompatibilities between let/const as implemented in V8 and >>> Spidermonkey and how they're specified in ES6 are an additional factor: >>> >>> * Per iteration loop binding (V8 and Spidermonkey don't do this for >>> let/const). >>> * TDZ. `x; const x = 10` works in V8 and Spidermonkey currently, specified >>> to throw ReferenceError in ES6 >>> >>> I think there's other differences. > > _______________________________________________ > es-discuss mailing list > [email protected] > https://mail.mozilla.org/listinfo/es-discuss > > _______________________________________________ es-discuss mailing list [email protected] https://mail.mozilla.org/listinfo/es-discuss
