Is \u006eew a valid Identifier?

Caitlin Potter caitpotter88 at gmail.com
Sat Nov 7 17:20:33 UTC 2015


You seem to be misunderstanding me

> On Nov 7, 2015, at 12:18 PM, Eric Suen <eric.suen.tech at gmail.com> wrote:
> 
> 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...
>> 
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> 
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