Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > comp.lang.javascript > #33460

Re: x === x

Show all headers | View raw

Ben Bacarisse wrote:

> Thomas 'PointedEars' Lahn <PointedEars@web.de> writes:
>> | > {} === {}
>> | <- false
>> | {} === {};
>> | (x) Uncaught SyntaxError: Unexpected token ===
>>
>> I assume that the explicit semicolon there is considered an
>> /EmptyStatement/ that switches back to statement context.
> 
> I can't find any reference to "statement context" or "expression
> context" in the language standard.  I assume it's your own terminology,
> but I don't see how it helps explain why [] === []; is OK but {} === {};
> is a syntax error.  (I know why, I'm just wondering how talking about
> === making expression context and ; switching back helps to explain this
> difference.)

Simply put, ECMAScript syntax is ambiguous, and it depends on the context 
how it is parsed.  For example, “{}” can be parsed either as an empty 
/Block/ *statement* (which can only be produced by the /Statement/ 
production) or as an empty Object initializer; the latter is an *expression* 
(it can only be produced by the /Expression/ production).  A further 
complication is the /ExpressionStatement/ production (IIRC).
 
I will consider the rest of your posting later.

-- 
PointedEars
FAQ: <http://PointedEars.de/faq> | <http://PointedEars.de/es-matrix>
<https://github.com/PointedEars> | <http://PointedEars.de/wsvn/>
Twitter: @PointedEars2 | Please do not cc me./Bitte keine Kopien per E-Mail.

Back to comp.lang.javascript | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread

Thread

Re: x === x Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-05-30 14:34 +0100
  Re: x === x Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-05-30 15:02 +0100
  Re: x === x Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2017-05-30 16:22 +0200
    Re: x === x Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-05-31 01:02 +0100
      Re: x === x Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2017-05-31 12:39 +0200
        Re: x === x Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-05-31 21:52 +0100
          Re: x === x Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2017-05-31 23:39 +0200
            Re: x === x Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-06-01 01:46 +0100
              Re: x === x Julio Di Egidio <julio@diegidio.name> - 2017-06-01 00:14 -0700
                Re: x === x John G Harris <niam@jghnorth.org.uk.invalid> - 2017-06-01 10:39 +0100
                Re: x === x Julio Di Egidio <julio@diegidio.name> - 2017-06-01 03:37 -0700
                Re: x === x John G Harris <niam@jghnorth.org.uk.invalid> - 2017-06-01 18:54 +0100
                Re: x === x Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-06-01 21:54 +0100
                Re: x === x John G Harris <niam@jghnorth.org.uk.invalid> - 2017-06-02 11:06 +0100
                Re: x === x John G Harris <niam@jghnorth.org.uk.invalid> - 2017-06-02 11:08 +0100
                Re: x === x John G Harris <niam@jghnorth.org.uk.invalid> - 2017-06-02 10:56 +0100
                Re: x === x Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-06-04 12:50 +0100
                Re: x === x John G Harris <niam@jghnorth.org.uk.invalid> - 2017-06-04 14:30 +0100
                Re: x === x Dr J R Stockton <J.R.Stockton@physics.org> - 2017-06-04 09:03 -0700
                Re: x === x Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-06-01 14:45 +0100
                Re: x === x Julio Di Egidio <julio@diegidio.name> - 2017-06-01 07:00 -0700
        Re: x === x Julio Di Egidio <julio@diegidio.name> - 2017-06-01 00:00 -0700

csiph-web