Re: Programming style question

From	"Jukka K. Korpela" <jkorpela@cs.tut.fi>
Newsgroups	comp.lang.javascript
Subject	Re: Programming style question
Date	2012-10-18 15:55 +0300
Organization	A noiseless patient Spider
Message-ID	<k5ou8b$kur$1@dont-email.me> (permalink)
References	<r_WdnX50haYCLeLNnZ2dnUVZ_vGdnZ2d@earthlink.com> <1538954.egObkdgl4n@PointedEars.de> <cfCdnQ0lM4FWbeLNnZ2dnUVZ_rmdnZ2d@earthlink.com> <k5ost7$d7o$1@dont-email.me> <0qGdnW4DceWJZeLNnZ2dnUVZ_gadnZ2d@earthlink.com>

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2012-10-18 15:37, Patricia Shanahan wrote:

> So your position is that a variable always has a value, possibly the
> undefined value, and the type belongs to the current value. Is that
> correct?

Yes. And this is what the ECMAScript standard says. It describes types 
of values, but not types of values at all. Right before clause 4.2.1 it 
says: "For example, a variable is not required to have its type declared 
nor are types associated with properties". The first part might be 
misleading - it's not just that they are not required to have their 
types declared, they *cannot* have their types declared, as becomes 
clear after reading the standard and seeing that there is no construct 
for the purpose.

>> However, it is essential to note that the mechanisms of the language
>> do not protect you from "type errors" in the sense as in many other
>> languages where you get a compile-time or run-time message about
>> assignment of a value of a wrong type. Neither do you get automatic
>> type conversions based on the type of a variable - simply because
>> variables do not have types in JavaScript.
>
> Yes, I've noticed that, and understand that if I really need e.g. a
> parameter to be a number, I need to check that at run time.

Well, you could also rely on automatic type conversions. Whether this is 
good practice is debatable (and depends), but the point is that type 
conversions do take place in JavaScript - but not according to the type 
of a variable. The conversions depend on the *use* of *values*.

Consider this:

var a = 10;
a = a + '5';

Here the original value of a gets converted to a string, because the 
value is used in an expression with the "+" operator and a string as the 
other operand. So '10' and '5' are concatenated, yielding '105'. This 
does not depend on the type of the variable a at all (it has no type); 
the same conversion appears when an expression has just literals as 
operands: 10 + '5'.

-- 
Yucca, http://www.cs.tut.fi/~jkorpela/

Thread

Programming style question Patricia Shanahan <pats@acm.org> - 2012-10-18 08:32 +0100
  Re: Programming style question "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2012-10-18 10:23 +0200
    Re: Programming style question Patricia Shanahan <pats@acm.org> - 2012-10-18 13:42 +0100
      Re: Programming style question "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2012-10-18 17:59 +0200
        Re: Programming style question Gene Wirchenko <genew@ocis.net> - 2012-10-18 09:56 -0700
          Re: Programming style question "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2012-10-19 00:49 +0200
            Re: Programming style question Gene Wirchenko <genew@ocis.net> - 2012-10-19 11:04 -0700
              Re: Programming style question "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2012-10-20 11:52 +0200
            Re: Programming style question Patricia Shanahan <pats@acm.org> - 2012-10-19 12:06 -0700
              Re: Programming style question Tim Streater <timstreater@greenbee.net> - 2012-10-19 23:12 +0100
                Re: Programming style question "Mel Smith" <med_cutout_syntel@aol.com> - 2012-10-19 21:56 -0600
              Re: Programming style question Bart Van der Donck <bart@nijlen.com> - 2012-10-20 02:21 -0700
                Re: Programming style question "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2012-10-20 12:03 +0200
                Re: Programming style question Patricia Shanahan <pats@acm.org> - 2012-10-20 06:31 -0700
                Re: Programming style question "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2012-10-20 18:30 +0200
                Re: Programming style question Patricia Shanahan <pats@acm.org> - 2012-10-20 10:32 -0700
                Re: Programming style question Tim Streater <timstreater@greenbee.net> - 2012-10-20 22:34 +0100
                Re: Programming style question "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2012-10-21 10:12 +0200
                Re: Programming style question Tim Streater <timstreater@greenbee.net> - 2012-10-21 09:34 +0100
                Re: Programming style question Dr J R Stockton <reply1242@merlyn.demon.co.uk.invalid> - 2012-10-21 17:59 +0100
                Re: Programming style question "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2012-10-22 09:55 +0200
                Re: Programming style question Tim Streater <timstreater@greenbee.net> - 2012-10-22 09:50 +0100
                Re: Programming style question Patricia Shanahan <pats@acm.org> - 2012-10-22 04:49 -0700
                Re: Programming style question Tim Streater <timstreater@greenbee.net> - 2012-10-22 14:04 +0100
                Re: Programming style question Hans-Georg Michna <hans-georgNoEmailPlease@michna.com> - 2012-10-22 16:07 +0200
                Re: Programming style question Dr J R Stockton <reply1243@merlyn.demon.co.uk.invalid> - 2012-10-23 18:22 +0100
                Re: Programming style question Hans-Georg Michna <hans-georgNoEmailPlease@michna.com> - 2012-10-22 16:01 +0200
                Re: Programming style question Jim T. <x@y.z> - 2012-10-22 12:16 -0400
                Re: Programming style question Patricia Shanahan <pats@acm.org> - 2012-10-22 11:40 -0700
                Re: Programming style question Gene Wirchenko <genew@ocis.net> - 2012-10-22 14:01 -0700
                Re: Programming style question Hans-Georg Michna <hans-georgNoEmailPlease@michna.com> - 2012-10-23 10:07 +0200
                Re: Programming style question Gene Wirchenko <genew@ocis.net> - 2012-10-23 09:43 -0700
                Re: Programming style question "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2012-10-23 11:49 +0200
                Re: Programming style question Jim T. <x@y.z> - 2012-10-23 15:52 -0400
                Re: Programming style question Patricia Shanahan <pats@acm.org> - 2012-10-23 13:07 -0700
                Re: Programming style question "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2012-10-23 22:45 +0200
                Re: Programming style question Gene Wirchenko <genew@ocis.net> - 2012-10-23 14:14 -0700
                Re: Programming style question "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2012-10-24 09:35 +0200
                Re: Programming style question Gene Wirchenko <genew@ocis.net> - 2012-10-24 10:17 -0700
                Re: Programming style question Dr J R Stockton <reply1243@merlyn.demon.co.uk.invalid> - 2012-10-25 18:41 +0100
                Re: Programming style question Patricia Shanahan <pats@acm.org> - 2012-10-25 17:03 -0700
                Re: Programming style question Gene Wirchenko <genew@ocis.net> - 2012-10-25 20:14 -0700
                Re: Programming style question Patricia Shanahan <pats@acm.org> - 2012-10-25 20:46 -0700
                Re: Programming style question "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2012-10-26 09:55 +0200
                Re: Programming style question Patricia Shanahan <pats@acm.org> - 2012-10-26 06:18 -0700
                Re: Programming style question "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2012-10-26 17:43 +0200
                Re: Programming style question Gene Wirchenko <genew@ocis.net> - 2012-10-26 09:57 -0700
                Re: Programming style question Patricia Shanahan <pats@acm.org> - 2012-10-26 10:24 -0700
                Re: Programming style question Gene Wirchenko <genew@ocis.net> - 2012-10-26 14:18 -0700
                Re: Programming style question Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2012-10-27 10:45 +0200
                Re: Programming style question "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2012-10-27 12:58 +0200
                Re: Programming style question Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2012-10-27 16:18 +0200
                Re: Programming style question "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2012-10-27 18:08 +0200
                Re: Programming style question Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2012-10-27 18:26 +0200
                Re: Programming style question "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2012-10-27 19:43 +0200
                Re: Programming style question Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2012-10-27 21:09 +0200
                Re: Programming style question "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2012-10-27 22:53 +0200
                Re: Programming style question John G Harris <john@nospam.demon.co.uk> - 2012-10-28 11:37 +0000
                Re: Programming style question Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2012-10-28 12:50 +0100
                Re: Programming style question Martin Leese <please@see.Web.for.e-mail.INVALID> - 2012-10-28 13:43 -0600
                Re: Programming style question "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2012-10-28 23:58 +0100
                Re: Programming style question John G Harris <john@nospam.demon.co.uk> - 2012-10-29 11:18 +0000
                Re: Programming style question Eric Bednarz <bednarz@fahr-zur-hoelle.org> - 2012-10-27 23:58 +0200
                Re: Programming style question Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2012-10-28 12:43 +0100
                Re: Programming style question Dr J R Stockton <reply1243@merlyn.demon.co.uk.invalid> - 2012-10-27 19:44 +0100
                Re: Programming style question Patricia Shanahan <pats@acm.org> - 2012-10-24 12:06 -0700
                Re: Programming style question Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2012-10-24 21:27 +0200
                Re: Programming style question Gene Wirchenko <genew@ocis.net> - 2012-10-24 15:12 -0700
                Re: Programming style question Tim Streater <timstreater@greenbee.net> - 2012-10-25 01:29 +0100
                Re: Programming style question Stefan Weiss <krewecherl@gmail.com> - 2012-10-24 21:25 +0200
                Re: Programming style question Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2012-10-24 21:57 +0200
                Re: Programming style question Stefan Weiss <krewecherl@gmail.com> - 2012-10-25 01:11 +0200
                Re: Programming style question Christoph Becker <cmbecker69@gmx.de> - 2012-10-25 02:00 +0200
                Re: Programming style question Scott Sauyet <scott.sauyet@gmail.com> - 2012-10-24 20:27 -0700
                Re: Programming style question Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2012-10-25 08:44 +0200
                Re: Programming style question Adam Silver <adambsilver@gmail.com> - 2012-10-25 04:28 -0700
                Re: Programming style question Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2012-10-25 23:18 +0200
                Re: Programming style question Scott Sauyet <scott.sauyet@gmail.com> - 2012-10-26 08:24 -0700
                Re: Programming style question Stefan Weiss <krewecherl@gmail.com> - 2012-11-07 22:13 +0100
                Re: Programming style question Tim Streater <timstreater@greenbee.net> - 2012-11-07 21:51 +0000
                Re: Programming style question Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2012-11-07 23:47 +0100
                Re: Programming style question Stefan Weiss <krewecherl@gmail.com> - 2012-11-08 01:14 +0100
                Re: Programming style question Gene Wirchenko <genew@ocis.net> - 2012-11-07 16:51 -0800
                Re: Programming style question "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2012-11-08 16:45 +0100
                Re: Programming style question Scott Sauyet <scott.sauyet@gmail.com> - 2012-11-08 08:02 -0800
                Re: Programming style question "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2012-11-08 17:39 +0100
                Re: Programming style question Gene Wirchenko <genew@ocis.net> - 2012-11-08 11:25 -0800
                Re: Programming style question "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2012-11-08 22:25 +0100
                Re: Programming style question John G Harris <john@nospam.demon.co.uk> - 2012-11-09 10:19 +0000
                Re: Programming style question "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2012-11-09 17:41 +0100
                Re: Programming style question Dr J R Stockton <reply1245@merlyn.demon.co.uk.invalid> - 2012-11-10 22:38 +0000
                Re: Programming style question Scott Sauyet <scott.sauyet@gmail.com> - 2012-10-22 12:32 -0700
                Re: Programming style question Hans-Georg Michna <hans-georgNoEmailPlease@michna.com> - 2012-10-23 10:05 +0200
                Re: Programming style question Christoph Becker <cmbecker69@gmx.de> - 2012-10-22 22:11 +0200
                Re: Programming style question Stefan Weiss <krewecherl@gmail.com> - 2012-10-23 02:42 +0200
                Re: Programming style question Hans-Georg Michna <hans-georgNoEmailPlease@michna.com> - 2012-10-23 10:08 +0200
              Re: Programming style question "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2012-10-20 18:34 +0200
  Re: Programming style question Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2012-10-18 11:57 +0200
    Re: Programming style question Patricia Shanahan <pats@acm.org> - 2012-10-18 13:06 +0100
      Re: Programming style question "Jukka K. Korpela" <jkorpela@cs.tut.fi> - 2012-10-18 15:32 +0300
        Re: Programming style question Patricia Shanahan <pats@acm.org> - 2012-10-18 13:37 +0100
          Re: Programming style question "Jukka K. Korpela" <jkorpela@cs.tut.fi> - 2012-10-18 15:55 +0300
          Re: Programming style question John G Harris <john@nospam.demon.co.uk> - 2012-10-19 10:12 +0100
            Re: Programming style question Patricia Shanahan <pats@acm.org> - 2012-10-19 07:24 -0700
              Re: Programming style question John G Harris <john@nospam.demon.co.uk> - 2012-10-20 17:47 +0100
          Re: Programming style question Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2012-10-24 01:15 +0100
            Re: Programming style question Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2012-10-24 01:31 +0100
            Re: Programming style question "Jukka K. Korpela" <jkorpela@cs.tut.fi> - 2012-10-24 07:34 +0300
              Re: Programming style question Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2012-10-24 19:57 +0200
                Re: Programming style question "Jukka K. Korpela" <jkorpela@cs.tut.fi> - 2012-10-24 21:02 +0300
        Re: Programming style question Patricia Shanahan <pats@acm.org> - 2012-10-18 20:15 -0700
      Re: Programming style question Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2012-10-24 01:21 +0100
  Re: Programming style question Scott Sauyet <scott.sauyet@gmail.com> - 2012-10-21 17:57 -0700

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