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Re: Difference between findPos("divThis") and findPos(divThis)

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On Nov 14, 5:14 am, J.R. wrote:
> On 14/11/2011 00:37, Denis McMahon wrote:
>> On Sun, 13 Nov 2011 20:49:25 -0200, J.R. wrote:
>
>>> it is one of the JavaScript best practices to declare all of the
>>> variables used in a function at the top of the function body. You
>>> may have many variables separated by commas, e.g
>
>>>     var el = ...,
>>>         h = ...,
>>>         w = ...,
>>>         i, j, len, ..., z;
>
>>> You must not use multiple var statements such as:
>>>     var el;
>>>     var h = ...;
>>>     var z;
>
>> Rubbish.
>
>> You can use as many var statements as you like. Nothing in the
>> standards or the implementation prevents this, so "must not" is
>> incorrect.
>
> "must not" was exaggerated on purpose, because using many var
> statements is an antipattern in JavaScript.

<URL: http://en.wikipedia.org/wiki/Anti-pattern > describes an
antipattern as:-

"In software engineering, an anti-pattern (or antipattern) is a
pattern that may be commonly used but is ineffective and/or
counterproductive in practice."

- which seems to require ineffective and/or counterproductive, both of
which could be demonstrated if true. However, ineffective is obviously
not relevant to variable declarations, as they are effective, with
near zero difference in behaviour between single variable declaration
statements and multiple variable declaration statements. So it is
counterproductive that seems pertinent, and given that this thread has
already demonstrated that continuing a statement across multiple lines
with each line except the last terminated with a comma is far from an
error resistant practice, the 'productivity' balance seems to already
have tipped away from this practice..

Personally I think that the comma is too visually indistinct and also
too visually similar to a semicolon to be a good candidate for source
code line termination.  That is, it is not easy to see that you have
done the right thing while writing it, and it is also not easy for a
later reader to see what the code is attempting to do (and doing it
correctly or not). I tend to see opaque source code text as
counterproductive in itself.

>> Some people think all variables should be declared in a single
>> statement.

That would be ridiculously dogmatic of them.

>> Some people use a different statement for each type
>> of variable, where type is the sort of data that it will be used
>> to hold (array, string, integer, float, object etc).
>> Some people just use one variable per var.

And some people put variable declarations on a single line until that
line starts to get too long (for some arbitrary definition of too long
(or a formal coding standard if applicable) and the start a new
variable declaration statement on the next line.

> The advantages of using the Single var Pattern at the top of your
> functions are:
> - there's a single place to look for all the local variables needed
> by the function;

This is not an advantage over multiple consecutive variable
declaration statements at the top of that same function. And since a
single statement could become very long or extended over multiple
lines that is likely to become difficult to read and understand,
negating some of the advantage of only looking in a single place.

> - prevention of logical errors when a variable is used before it’s
> defined;

This is not an advantage over multiple consecutive variable
declaration statements at the top of that same function. And what do
"logical errors" consist of in this context? If variables are declared
they are declared as an execution context is entered.

In my experience when people have made a case for declaring variables
at the top of a function body it is on order that the structure/order
of the source code reflect the way in which the javascript engine is
going to behave (handling the declarations before any actual code
execution). It would seem an unjustified misapplication of this
justification to insist that those variable declarations be confined
to a single statement (especially since that same recommendation wants
the inner function declarations to appear at the top of the function
body as well, and they cannot be combined into a single statement).

> - Helps you remember to declare variables and therefore minimize
> globals;

This is not an advantage over multiple consecutive variable
declaration statements at the top of that same function.

> - only one var statement means less code to type and a reduction
> in the file size.

So it would be (at best) the opportunity to save half a dozen bytes
that is the only factor left that could justify the "antipattern"
assertion, on the grounds of the alternatives being
counterproductive.  I won't be buying that argument as this would be
neutralised by zipping the resource to be sent to the client, while
the potential added obscurity in the source code looks too negative to
me.

>> These are all permitted by the various standards, and they all
>> work. There is no reason that you "must" or "must not" do any
>> of these.
>
>> Also, "best practice" is invariably "in the opinion of the author
>> of the website / book / blog / whatever" that said example of best
>> practice appears in.
>
> There are patterns in any programming language usually adopted
> by programmers as "best coding practices". And it happens to
> other fields of study too. See
> <http://en.wikipedia.org/wiki/Best_Coding_Practices>

Maybe, but a high proportion of "best practices" that have been
proposed for javascript have been pretty much BS. Misunderstandings/
miscomprehensions abound, but the people looking for rules that will
supposedly help them cannot easily tell. I always recommend that no
"best practice" should be taken seriously unless it is presented
alongside a reasoned justification, and that that justification stands
up to critical scrutiny. For anything that really is a "best practice"
that should be an achievable requirement.

And having seen your reasoning for only using a single variable
declaration statement per function body, it didn’t stand up.

> If you get a bunch of authors (books, blogs, etc.) that state the
> same "best practices" in any programming language, then you can
> bet who is wrong or right...

Not with javascript. Nonsense propagates like wildfire in this field.
Hence the need to look at the actual reasoning and not be impressed by
any argument from numbers.

>> As a matter of interest, what's your reference for "best
>> practice"? If I write a book or start a blog called "Javascript
>> - Best Practice" does that make it true?
>
> No, it doesn't, although I know you're a very experienced and
> smart programmer.

Do you really know that? (and should it matter anyway as in isolation
that would only make for an argument from authority?)

> However, if you published some evidence such
> as performance tests, etc.,

Yes, test cases are really good at demonstrating a point. Indeed if
properly designed are much more convincing than reasoned argument. So
can the alternatives to using a single variable declaration statement
at the start of a function body be demonstrated to be
counterproductive with some test case?

> then you could state that some practice
> should be either considered a good one or avoided altogether.

Performance isn't everything. In practice most javascript performs
just fine (and ironically better and better as CPUs and javascript
engines get faster). It will be useful to know what factors impact
performance, so as to be able to achieve it when necessary or avoid
squandering it, but it has long been the case that the biggest expense
in software production is accounted for by code maintenance, making
source code clarity (readability, understandably and self-documenting-
ness) a completely valid subject for "best practices", and putting the
variable declarations at the top of a function body was originally
primarily about code clarity.

Richard.

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Thread

Difference between findPos("divThis") and findPos(divThis) " Cal Who" <CalWhoNOSPAM@roadrunner.com> - 2011-11-13 09:51 -0500
  Re: Difference between findPos("divThis") and findPos(divThis) Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2011-11-13 18:25 +0100
    Re: Difference between findPos("divThis") and findPos(divThis) " Cal Who" <CalWhoNOSPAM@roadrunner.com> - 2011-11-13 13:58 -0500
      Re: Difference between findPos("divThis") and findPos(divThis) Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2011-11-13 20:26 +0100
        Re: Difference between findPos("divThis") and findPos(divThis) " Cal Who" <CalWhoNOSPAM@roadrunner.com> - 2011-11-13 15:04 -0500
          Re: Difference between findPos("divThis") and findPos(divThis) "J.R." <groups_jr-1@yahoo.com.br> - 2011-11-13 18:55 -0200
            Re: Difference between findPos("divThis") and findPos(divThis) "J.R." <groups_jr-1@yahoo.com.br> - 2011-11-13 18:59 -0200
              Re: Difference between findPos("divThis") and findPos(divThis) " Cal Who" <CalWhoNOSPAM@roadrunner.com> - 2011-11-13 17:10 -0500
                Re: Difference between findPos("divThis") and findPos(divThis) "J.R." <groups_jr-1@yahoo.com.br> - 2011-11-13 20:49 -0200
                Re: Difference between findPos("divThis") and findPos(divThis) " Cal Who" <CalWhoNOSPAM@roadrunner.com> - 2011-11-13 20:00 -0500
                Re: Difference between findPos("divThis") and findPos(divThis) Denis McMahon <denismfmcmahon@gmail.com> - 2011-11-14 02:37 +0000
                Re: Difference between findPos("divThis") and findPos(divThis) "J.R." <groups_jr-1@yahoo.com.br> - 2011-11-14 03:14 -0200
                Re: Difference between findPos("divThis") and findPos(divThis) Denis McMahon <denismfmcmahon@gmail.com> - 2011-11-14 14:03 +0000
                Re: Difference between findPos("divThis") and findPos(divThis) "J.R." <groups_jr-1@yahoo.com.br> - 2011-11-14 14:14 -0200
                Re: Difference between findPos("divThis") and findPos(divThis) Denis McMahon <denismfmcmahon@gmail.com> - 2011-11-14 18:31 +0000
                Re: Difference between findPos("divThis") and findPos(divThis) "Evertjan." <exjxw.hannivoort@interxnl.net> - 2011-11-14 18:36 +0000
                Re: Difference between findPos("divThis") and findPos(divThis) Denis McMahon <denismfmcmahon@gmail.com> - 2011-11-15 00:18 +0000
                Re: Difference between findPos("divThis") and findPos(divThis) Scott Sauyet <scott.sauyet@gmail.com> - 2011-11-14 10:54 -0800
                Re: Difference between findPos("divThis") and findPos(divThis) "Richard Cornford" <Richard@litotes.demon.co.uk> - 2011-11-15 01:23 +0000
                Re: Difference between findPos("divThis") and findPos(divThis) Scott Sauyet <scott.sauyet@gmail.com> - 2011-11-16 06:04 -0800
                Re: Difference between findPos("divThis") and findPos(divThis) Frobernik <nospam@nospam.com> - 2011-11-17 22:06 +0000
                Re: Difference between findPos("divThis") and findPos(divThis) Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2011-11-17 23:54 +0100
                Re: Difference between findPos("divThis") and findPos(divThis) Frobernik <nospam@nospam.com> - 2011-11-18 09:33 +0000
                Function arguments vs. local variables (was: Difference between findPos("divThis") and findPos(divThis)) Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2011-11-19 16:05 +0100
                Re: Function arguments vs. local variables Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2011-11-19 18:17 +0100
                Re: Function arguments vs. local variables Frobernik <nospam@nospam.com> - 2011-11-21 20:01 +0000
                Re: Function arguments vs. local variables Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2011-11-22 12:50 +0100
                Re: Difference between findPos("divThis") and findPos(divThis) Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2011-11-14 15:04 +0100
                Re: Difference between findPos("divThis") and findPos(divThis) John G Harris <john@nospam.demon.co.uk> - 2011-11-14 15:13 +0000
                Re: Difference between findPos("divThis") and findPos(divThis) Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2011-11-14 18:27 +0100
                Re: Difference between findPos("divThis") and findPos(divThis) Eric Bednarz <bednarz@fahr-zur-hoelle.org> - 2011-11-14 17:52 +0100
                Re: Difference between findPos("divThis") and findPos(divThis) "J.R." <groups_jr-1@yahoo.com.br> - 2011-11-14 15:07 -0200
                Re: Difference between findPos("divThis") and findPos(divThis) Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2011-11-14 18:19 +0100
                Re: Difference between findPos("divThis") and findPos(divThis) "J.R." <groups_jr-1@yahoo.com.br> - 2011-11-14 15:44 -0200
                Re: Difference between findPos("divThis") and findPos(divThis) Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2011-11-14 19:01 +0100
                Re: Difference between findPos("divThis") and findPos(divThis) "J.R." <groups_jr-1@yahoo.com.br> - 2011-11-14 16:42 -0200
                Re: Difference between findPos("divThis") and findPos(divThis) Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2011-11-14 19:53 +0100
                Re: Difference between findPos("divThis") and findPos(divThis) Richard Cornford <Richard@litotes.demon.co.uk> - 2011-11-14 09:18 -0800
                Re: Difference between findPos("divThis") and findPos(divThis) "J.R." <groups_jr-1@yahoo.com.br> - 2011-11-14 16:22 -0200
                Re: Difference between findPos("divThis") and findPos(divThis) Denis McMahon <denismfmcmahon@gmail.com> - 2011-11-14 18:38 +0000
                Re: Difference between findPos("divThis") and findPos(divThis) Gene Wirchenko <genew@ocis.net> - 2011-11-14 12:12 -0800
                Re: Difference between findPos("divThis") and findPos(divThis) Gene Wirchenko <genew@ocis.net> - 2011-11-14 12:00 -0800
                Re: Difference between findPos("divThis") and findPos(divThis) " Cal Who" <CalWhoNOSPAM@roadrunner.com> - 2011-11-14 08:48 -0500
                Re: Difference between findPos("divThis") and findPos(divThis) Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2011-11-14 13:15 +0100
                Re: Difference between findPos("divThis") and findPos(divThis) "J.R." <groups_jr-1@yahoo.com.br> - 2011-11-14 13:03 -0200
                Re: Difference between findPos("divThis") and findPos(divThis) Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2011-11-14 17:24 +0100
          Re: Difference between findPos("divThis") and findPos(divThis) Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2011-11-14 13:00 +0100
        Re: Difference between findPos("divThis") and findPos(divThis) John G Harris <john@nospam.demon.co.uk> - 2011-11-14 15:05 +0000

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