Is \u006eew a valid Identifier?

Eric Suen eric.suen.tech at gmail.com
Sat Nov 7 17:18:13 UTC 2015


get/set/as/from/target are valid Identifier, it can't be reserved words

On Sun, Nov 8, 2015 at 1:06 AM, Caitlin Potter <caitpotter88 at gmail.com> wrote:
> It should be reserved, logically — but the spec does not explicitly forbid
> this. Unless you take Allen’s “it’s a bold sequence of characters,
> therefore…” argument, which is all well and good, but is only really
> explained in the spec in http://tc39.github.io/ecma262/#sec-grammar-notation
> in the first paragraph — and then further, unicode escapes tend to be
> eagerly converted, so “appear in a script exactly as written” can be
> misleading. Explicit static semantics work a lot better for this sort of
> thing, as they can be easily referenced.
>
> So, in that case, it’s SpiderMonkey with the bug in the case of accessor
> methods, and Chrome without it, while Firefox behaves correctly with escaped
> `new . target`, and Chrome doesn’t.
>
>
> On Nov 7, 2015, at 11:57 AM, Eric Suen <eric.suen.tech at gmail.com> wrote:
>
> So escaped ReservedWords are not valid as ReservedWords nor
> Identifier, what is it then?
>
> And in export { IdentifierName }, why it's IdentifierName not
> Identifier. since IdentifierName only valid as Property in
> ObjectLiteral or Method in Class, is there any way to define
> ReservedWords as local name?
>
> 'get'/'set' is ContextuallyReservedIdentifier, maybe that's the reason?
>
>
> On Sat, Nov 7, 2015 at 11:32 PM, Caitlin Potter <caitpotter88 at gmail.com>
> wrote:
>
> That it works in Chrome is a bug, which will hopefully be fixed by Monday or
> Tuesday!
>
> Per http://tc39.github.io/ecma262/#sec-keywords, “new” is a Keyword, which
> makes it a ReservedWord.
>
> Per
> http://tc39.github.io/ecma262/#sec-identifiers-static-semantics-early-errors,
> under the
> “Identifier: IdentifierName but not ReservedWord” section, the second early
> error applies here. This applies to
> `new`, which is always a reserved word. So whenever an Identifier is
> expected, if it contains UnicodeEscapeSequences which result in the same
> StringValue as a ReservedWord, it’s an error.
>
> The spec is similarly explicit in saying that escaped ReservedWords are not
> valid as ReservedWords. Browsers behave differently here (for instance,
> http://jsfiddle.net/jd51pqae/ <<< at the time of this writing Webkit Nightly
> prints the text, while other browsers SyntaxError. in Chromes case, this is
> because it’s tokenized as an Identifier, so the second Identifier “f” is
> unexpected when parsing a MemberExpression. SpiderMonkey is doing a nice job
> of reporting clean errors for this kind of thing, that are easier to
> understand.
>
> There are some odd points though:
>
> 1. ReservedWord restrictions never apply to `get` or `set`, even in
> ObjectLiterals (though currently Chrome fails to treat `g\u{65}t` or
> `s\u{65}t` as an accessor prefix, this is a bug).
>
> 2. In the case of “new.target”, it’s technically legal to write
> `new.t\u{61}rget`, but this mostly just seems like an oversight in the spec.
>
> On Nov 7, 2015, at 9:50 AM, Eric Suen <eric.suen.tech at gmail.com> wrote:
>
> "The ReservedWord definitions are specified as literal sequences of
> specific SourceCharacter elements. A code point in a ReservedWord
> cannot be expressed by a \ UnicodeEscapeSequence." - what does it
> mean?
>
> The following code is valid in Chrome, but invalid in firefox and IE.
>
> var \u006eew = 1; // \u006e = 'n'
>
> and valid in Babel/Traceur, invalid in typescript/esprima...
>
> --
> ------------------------------------------------
> Spket IDE - Development Tool for RIA.
>
> http://www.spket.com
> _______________________________________________
> es-discuss mailing list
> es-discuss at mozilla.org
> https://mail.mozilla.org/listinfo/es-discuss
>
>
>
>
>
> --
> ------------------------------------------------
> Spket IDE - Development Tool for RIA.
>
> http://www.spket.com
>
>



-- 
------------------------------------------------
Spket IDE - Development Tool for RIA.

http://www.spket.com


More information about the es-discuss mailing list