Re: Why is this returning NaN

Message-ID	<1652233.QWaZaUHVxr@PointedEars.de> (permalink)
From	Thomas 'PointedEars' Lahn <PointedEars@web.de>
Organization	PointedEars Software (PES)
Date	2013-03-01 21:03 +0100
Subject	Re: Why is this returning NaN
Newsgroups	comp.lang.javascript
References	<kgi46g$ivc$1@dont-email.me> <kgi75q$2lf$1@dont-email.me> <kgp88e$p8o$1@speranza.aioe.org> <6062718.vzGJ4vAIZo@PointedEars.de> <kgqfsg$vdj$1@speranza.aioe.org>

Show all headers | View raw

Joao Rodrigues (J.R.) wrote:

> On 01/03/2013 08:46, Thomas 'PointedEars' Lahn wrote:
>> J.R. wrote:
>>> The OP'c code fails because converting new Date() to a string might
>>> produce give a different format than the string being used. […]
>> Nonsense.
> 
> I mistook the subtraction with the "==" operator.

If so, there is another misconception on your part.  In short:

1. new Date() == "2013/02/26 10:24:00"
2. ToPrimitive(new Date()) == "2013/02/26 10:24:00"
3. [[DefaultValue]](new Date()) == "2013/02/26 10:24:00"
4. Number(…) == "2013/02/26 10:24:00"
5. Number(…) == ToNumber("2013/02/26 10:24:00")
6. Number(…) == NaN
7. false

(“NaN” is not equal to anything, not even itself.  It can only be detected 
with isNaN(…)).

> Then I made a correction in my follow-up post, but it still was incomplete
> (forgive me as it was past midnight). Okay. Thanks.

Your “correction” was not incomplete; it was wrong.  The result “NaN” with 
the original code also is because the operands of “-” are converted to 
_Number_ (instead of String).  In short:

1. Math.abs(new Date() - "2013/02/26 10:24:00")
2. Math.abs(Number(new Date()) - Number("2013/02/26 10:24:00"))
3. Math.abs(Number(…) - NaN)
4. Math.abs(NaN)
5. NaN

(“NaN” is said to be “toxic”.)

There is another statement that I did not comment on but should have.  You 
said in your “correction”:

| Anyway, beware of implicit coercions in JavaScript.

To which I reply:

No; *learn* about implicit type _conversion_ in ECMAScript and its 
implementations, and *learn to leverage* its expressive power.

No offense meant or taken.

>>>> Better, use a suitable library to parse the date stamp or
>>>> construct the Date object using suitable numeric parameters.
>>>> There is no guarantee that all implementations will parse a
>>>> notation like 2013/02/26 10:24:00 (the same way).
>>>
>>> ACK.
>>
>> A Sith^WWannabe cries for their Master^W^Wlibraries when they get
>> stuck. A Jedi^W^WThe knowledgable uses the power of the
>> Force^Wlanguages instead:
>>
>> var s = "2013/02/26 10:24:00"; var m =
>> s.match(/^\s*(\d+)\/(\d+)\/(\d+)\s+(\d+):(\d+):(\d+)\s*$/); var d;
>>
>> if (m) { /* * But see also Function.prototype.construct() in
>> JSX:object.js * * --m[2]; * d = Date.construct(m.slice(1)); */ d =
>> new Date(m[1], m[2] - 1, m[3], m[4], m[5], m[6]); }
> 
> I think that he was talking about a personal library some developers
> create for their own use; I mean he was advising the use of neither
> date.js nor any other bloated library.

I do not know what he meant, but I doubt it was a “personal library”.  
Indeed, given his record, it is likely that he did mean such bloat.

-- 
PointedEars

Twitter: @PointedEars2
Please do not Cc: me. / Bitte keine Kopien per E-Mail.

Thread

Why is this returning NaN "Tony" <tony.johansson@inport.com> - 2013-02-26 11:54 +0100
  Re: Why is this returning NaN Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2013-02-26 12:09 +0100
  Re: Why is this returning NaN "Jukka K. Korpela" <jkorpela@cs.tut.fi> - 2013-02-26 13:45 +0200
    Re: Why is this returning NaN "J.R." <groups_jr-1@yahoo.com.br> - 2013-03-01 00:45 -0300
      Re: Why is this returning NaN "J.R." <groups_jr-1@yahoo.com.br> - 2013-03-01 01:13 -0300
        Re: Why is this returning NaN Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2013-03-01 12:48 +0100
      Re: Why is this returning NaN "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2013-03-01 10:06 +0100
      Re: Why is this returning NaN Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2013-03-01 12:46 +0100
        Re: Why is this returning NaN John G Harris <niam@jghnorth.org.uk.invalid> - 2013-03-01 14:19 +0000
        Re: Why is this returning NaN "Joao Rodrigues (J.R.)" <groups_jr-1@yahoo.com.br> - 2013-03-01 12:01 -0300
          Re: Why is this returning NaN Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2013-03-01 21:03 +0100
            Re: Why is this returning NaN "Joao Rodrigues (J.R.)" <groups_jr-1@yahoo.com.br> - 2013-03-01 18:25 -0300
              Re: Why is this returning NaN Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2013-03-01 22:35 +0100
                Re: Why is this returning NaN Patricia Shanahan <pats@acm.org> - 2013-03-01 20:31 -0800
                Re: Why is this returning NaN Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2013-03-02 12:49 +0100
                Re: Why is this returning NaN "J.R." <groups_jr-1@yahoo.com.br> - 2013-03-03 12:32 -0300
                Re: Why is this returning NaN "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2013-03-03 18:03 +0100
                Re: Why is this returning NaN Martin Leese <please@see.Web.for.e-mail.INVALID> - 2013-03-03 10:16 -0700
                OT: "javascript" was: Why is this returning NaN Christoph Becker <cmbecker69@gmx.de> - 2013-03-03 20:35 +0100
                Re: OT: "javascript" was: Why is this returning NaN "Jukka K. Korpela" <jkorpela@cs.tut.fi> - 2013-03-03 21:43 +0200
                Re: OT: "javascript" was: Why is this returning NaN Tim Streater <timstreater@greenbee.net> - 2013-03-03 19:45 +0000
                "javascript" (was: OT: "javascript") Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2013-03-03 21:09 +0100
                Re: "javascript" "J.R." <groups_jr-1@yahoo.com.br> - 2013-03-03 23:19 -0300
                Re: "javascript" Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2013-03-04 11:27 +0100
                Re: "javascript" Tim Streater <timstreater@greenbee.net> - 2013-03-04 13:09 +0000
                Re: "javascript" Christoph Becker <cmbecker69@gmx.de> - 2013-03-10 20:50 +0100
                Re: "javascript" Tim Streater <timstreater@greenbee.net> - 2013-03-10 20:29 +0000
                Re: "javascript" Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2013-03-10 23:23 +0100
                Re: "javascript" Tim Streater <timstreater@greenbee.net> - 2013-03-10 22:48 +0000
                Re: "javascript" Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2013-03-10 23:53 +0100
                Re: "javascript" Tim Streater <timstreater@greenbee.net> - 2013-03-10 23:23 +0000
                Re: "javascript" Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2013-03-11 02:57 +0100
                Re: "javascript" Tim Streater <timstreater@greenbee.net> - 2013-03-11 08:55 +0000
                Re: "javascript" Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2013-03-11 17:38 +0100
                Re: "javascript" Dr J R Stockton <reply1300@merlyn.demon.co.uk.invalid> - 2013-03-12 19:29 +0000
                Re: "javascript" Andrew Poulos <ap_prog@hotmail.com> - 2013-03-13 14:36 +1100
                Re: "javascript" John G Harris <niam@jghnorth.org.uk.invalid> - 2013-03-13 15:20 +0000
                Re: "javascript" Andrew Poulos <ap_prog@hotmail.com> - 2013-03-14 11:18 +1100
                Re: "javascript" John G Harris <niam@jghnorth.org.uk.invalid> - 2013-03-14 10:43 +0000
                Re: "javascript" Andrew Poulos <ap_prog@hotmail.com> - 2013-03-15 07:02 +1100
                Re: "javascript" John G Harris <niam@jghnorth.org.uk.invalid> - 2013-03-15 10:28 +0000
                Re: "javascript" Andrew Poulos <ap_prog@hotmail.com> - 2013-03-16 07:17 +1100
                Re: "javascript" John G Harris <niam@jghnorth.org.uk.invalid> - 2013-03-16 12:04 +0000
                Re: "javascript" Andrew Poulos <ap_prog@hotmail.com> - 2013-03-17 08:17 +1100
                Re: "javascript" John G Harris <niam@jghnorth.org.uk.invalid> - 2013-03-17 11:13 +0000
                Re: "javascript" Andrew Poulos <ap_prog@hotmail.com> - 2013-03-17 23:15 +1100
                Re: "javascript" John G Harris <niam@jghnorth.org.uk.invalid> - 2013-03-17 16:42 +0000
                Re: "javascript" Andrew Poulos <ap_prog@hotmail.com> - 2013-03-18 07:47 +1100
                Re: "javascript" John G Harris <niam@jghnorth.org.uk.invalid> - 2013-03-18 15:01 +0000
                Re: "javascript" Andrew Poulos <ap_prog@hotmail.com> - 2013-03-19 07:34 +1100
                Re: "javascript" John G Harris <niam@jghnorth.org.uk.invalid> - 2013-03-19 15:04 +0000
                Re: "javascript" Andrew Poulos <ap_prog@hotmail.com> - 2013-03-20 07:40 +1100
                Re: "javascript" Mike Duffy <Use.web.form@website_in_sig.com> - 2013-03-13 12:03 +0000
                Re: "javascript" Dr J R Stockton <reply1300@merlyn.demon.co.uk.invalid> - 2013-03-14 21:22 +0000
                Re: "javascript" Mike Duffy <Use.web.form@website_in_sig.com> - 2013-03-15 01:44 +0000
                Re: "javascript" Dr J R Stockton <reply1300@merlyn.demon.co.uk.invalid> - 2013-03-16 19:42 +0000
                Re: "javascript" Mike Duffy <Use.web.form@website_in_sig.com> - 2013-03-17 18:25 +0000
                Re: "javascript" Tim Streater <timstreater@greenbee.net> - 2013-03-17 19:01 +0000
                Re: "javascript" Gene Wirchenko <genew@telus.net> - 2013-03-15 10:55 -0700
                Re: "javascript" John G Harris <niam@jghnorth.org.uk.invalid> - 2013-03-13 15:21 +0000
                Re: "javascript" (was: OT: "javascript") Dr J R Stockton <reply1300@merlyn.demon.co.uk.invalid> - 2013-03-04 13:07 +0000
                Re: "javascript" Christoph Becker <cmbecker69@gmx.de> - 2013-03-10 20:34 +0100
                Re: "javascript" Tim Streater <timstreater@greenbee.net> - 2013-03-10 19:39 +0000
                Re: OT: "javascript" was: Why is this returning NaN "J.R." <groups_jr-1@yahoo.com.br> - 2013-03-03 22:41 -0300
                Re: OT: "javascript" was: Why is this returning NaN "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2013-03-04 09:57 +0100
                Re: OT: "javascript" was: Why is this returning NaN Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2013-03-04 11:25 +0100
                Re: OT: "javascript" was: Why is this returning NaN John G Harris <niam@jghnorth.org.uk.invalid> - 2013-03-04 14:52 +0000
                Re: OT: "javascript" was: Why is this returning NaN Eric Bednarz <bednarz@fahr-zur-hoelle.org> - 2013-03-10 01:02 +0100
                Re: OT: "javascript" was: Why is this returning NaN John G Harris <niam@jghnorth.org.uk.invalid> - 2013-03-10 10:52 +0000
                Re: OT: "javascript" was: Why is this returning NaN Eric Bednarz <bednarz@fahr-zur-hoelle.org> - 2013-03-10 12:44 +0100
                Re: OT: "javascript" was: Why is this returning NaN John G Harris <niam@jghnorth.org.uk.invalid> - 2013-03-10 17:49 +0000
                Re: OT: "javascript" was: Why is this returning NaN Eric Bednarz <bednarz@fahr-zur-hoelle.org> - 2013-03-20 01:21 +0100
                Re: OT: "javascript" was: Why is this returning NaN John G Harris <niam@jghnorth.org.uk.invalid> - 2013-03-20 15:25 +0000
                Re: OT: "javascript" was: Why is this returning NaN Eric Bednarz <bednarz@fahr-zur-hoelle.org> - 2013-03-30 01:28 +0100
  Re: Why is this returning NaN Tim Streater <timstreater@greenbee.net> - 2013-02-26 12:00 +0000
    Re: Why is this returning NaN Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2013-02-26 18:07 +0100
  Re: Why is this returning NaN Gregor Kofler <usenet@gregorkofler.com> - 2013-02-26 13:42 +0100
  Re: Why is this returning NaN Dr J R Stockton <reply1300@merlyn.demon.co.uk.invalid> - 2013-02-27 20:43 +0000
    Re: Why is this returning NaN "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2013-02-28 09:19 +0100

csiph-web