When is a function not a function?

[David Mark]

I've got a collection of functions that accept a function or object
(paired with a method name) as a callback.

For the longest time I have relied on this test.

(typeof cb == 'function')

This should work as well, but I am not sure how well it degrades in
older browsers. I think there are issues with functions created in
another context (eg frame) as well.

(cb instanceof Function)

Then I came across this.

(!!fn && typeof fn != "string" && !fn.nodeName && fn.constructor !=
Array && /function/i.test( fn + "" ))

I'm sure it is wrong as it is from jQuery, but it makes me wonder if
there are bugs in older browsers that will mislead my test.

As an aside, I was looking at the jQuery source as some browser
sniffer I was arguing with on a blog cited it as part of an "everybody
is doing it" argument. I had glanced at it previously and dismissed
it based on its resemblance to Prototype. Upon closer inspection, it
makes Prototype look inspired. Suffice to say that anybody who
recommends it hasn't read the code. It's a horror show.

[Randy Webb]

John G Harris said the following on 9/27/2007 3:37 PM:

On Wed, 26 Sep 2007 at 20:21:44, in comp.lang.javas cript, Randy Webb
wrote:

>Thomas 'PointedEars' Lahn said the following on 9/26/2007 5:40 PM:

>>Peter Michaux wrote:
On Sep 26, 1:02 pm, David Mark <dmark.cins...@ gmail.comwrote:
jQuery uses dollar sign variables, which I don't think are allowed
under the specification.
Dollar signs are allowed. See sec 7.6. The spec then says "The dollar
sign is intended for use only in mechanically generated code."
Which is exactly why jQuery should not.

But there is no reason why it *can not* other than people's pedantic
desires to whine about it. Had it been S that was used instead, people
would shut up about it and move on. Except that if it had been S
instead of $ then people would be whining about how the name wasn't an
indication of what it did.

But it's already happened :

Thou shalt not start a global name with "MM_".

Or __, ever heard of __doPostBack and the others? All of which are
naming clashes.

Because otherwise there will come a day when you get an obscure bug that
will drive you crazy.

That is true with any prefix though. Not just $ or MM or __

There's a similar rule in C++ about names starting with leading
underlines. The difference is that the rule has been biting people for
years, so competent programmers don't dismiss it as pedantic standards
mania.

Nice to know that about C++ but I don't see the relationship between C++
and/or Java (that Richard brought into it).

--
Randy
Chance Favors The Prepared Mind
comp.lang.javas cript FAQ - http://jibbering.com/faq/index.html
Javascript Best Practices - http://www.JavascriptToolbox.com/bestpractices/

[The Natural Philosopher]

dh**********@gm ail.com wrote:

On Oct 3, 9:59 am, Randy Webb <HikksNotAtH... @aol.comwrote:

>Richard Cornford said the following on 9/30/2007 4:36 PM:

>>Randy Webb wrote:

>It doesn't say "limited" or "required". It simply says "This is what it
is *intended* for". I doubt very seriously that 99% of what is done with
scripting was it's "intended use".

Either way, it doesn't matter what ECMA had to say about it, people are
still going to use it until some UA comes out that breaks it. And no
amount of discussing it in comp.lang.javas cript will ever change that.

Things that might seem not to matter:
{OOA&D, Testing, Variable names, comments, code formatting
conventions, process}

These things are just not that appealing to people, generally. This is
especially true for presentation layer development. Why not look at
what toolkit vendors do? They're the rock stars, right?

Yahoo still employs code freezes, status reports, and last time I was
there, my manager would not let me check ANY tests into CVS (they
still don't use SVN). They were calling this Scrum.

Little things like "don't use post-increment operator" are easy for
people to grasp. Free advice that comes with cookies and refreshments.
Serotonin levels go up with the increased blood sugar, jokes are told,
examples are shown (with much hand waving), and people are happy while
not working.

I do wonder though: Why $? I would like to know, out of curiosity, why
did jQuery use $? There is a reason the variable was used; I just
don't know what it is.

I would say ha about 90% of "standards" s not so much 'best practice' as
just plain simple 'do it this ways so that people coming upon you
unexpectedly will know what's going on'

E.g. we all drive on one side of the road, but which side is open to debate.

Standards are there mostly for people working together, to enforce a
common style, so everybody knows how things should be done.

Its a mark of the petty jobsworth to elect such standards into moral Laws.

>--
Randy
Chance Favors The Prepared Mind
comp.lang.java script FAQ -http://jibbering.com/faq/index.html
Javascript Best Practices -http://www.JavascriptT oolbox.com/bestpractices/

[Thomas 'PointedEars' Lahn]

dh**********@gm ail.com wrote:

I do wonder though: Why $? I would like to know, out of curiosity, why
did jQuery use $? There is a reason the variable was used; I just
don't know what it is.

Cluelessness. (That was easy.)
PointedEars
--
"Use any version of Microsoft Frontpage to create your site. (This won't
prevent people from viewing your source, but no one will want to steal it.)"
-- from <http://www.vortex-webdesign.com/help/hidesource.htm>

[Randy Webb]

Thomas 'PointedEars' Lahn said the following on 10/5/2007 9:14 AM:

dh**********@gm ail.com wrote:

>I do wonder though: Why $? I would like to know, out of curiosity, why
did jQuery use $? There is a reason the variable was used; I just
don't know what it is.

Cluelessness. (That was easy.)

And it is debatable who is the one possessing the "Cluelessne ss".

Why it was used is trivial to figure out.

P.S. YSCIB

--
Randy
Chance Favors The Prepared Mind
comp.lang.javas cript FAQ - http://jibbering.com/faq/index.html
Javascript Best Practices - http://www.JavascriptToolbox.com/bestpractices/

[Thomas 'PointedEars' Lahn]

Randy Webb wrote:

Thomas 'PointedEars' Lahn said the following on 10/5/2007 9:14 AM:

>dh**********@gm ail.com wrote:

>>I do wonder though: Why $? I would like to know, out of curiosity, why
did jQuery use $? There is a reason the variable was used; I just
don't know what it is.

Cluelessness . (That was easy.)

And it is debatable who is the one possessing the "Cluelessne ss".

Not understood.

Why it was used is trivial to figure out.

Then you can tell it for sure, yes?

P.S. YSCIB

-v
PointedEars
--
var bugRiddenCrashP ronePieceOfJunk = (
navigator.userA gent.indexOf('M SIE 5') != -1
&& navigator.userA gent.indexOf('M ac') != -1
) // Plone, register_functi on.js:16

[Randy Webb]

Thomas 'PointedEars' Lahn said the following on 10/5/2007 7:37 PM:

Randy Webb wrote:

>Thomas 'PointedEars' Lahn said the following on 10/5/2007 9:14 AM:

>>dh**********@gm ail.com wrote:
I do wonder though: Why $? I would like to know, out of curiosity, why
did jQuery use $? There is a reason the variable was used; I just
don't know what it is.
Cluelessnes s. (That was easy.)

And it is debatable who is the one possessing the "Cluelessne ss".

Not understood.

Try enabling the spell checker in Thunderbird. It might shed some light
on it.

>Why it was used is trivial to figure out.

Then you can tell it for sure, yes?

Sure I can. It was chosen because of the uniqueness of it and the lack
of use of it on the web. What better way to pick a simple single
character identifier than one that wasn't in use?

--
Randy
Chance Favors The Prepared Mind
comp.lang.javas cript FAQ - http://jibbering.com/faq/index.html
Javascript Best Practices - http://www.JavascriptToolbox.com/bestpractices/

[Thomas 'PointedEars' Lahn]

Randy Webb wrote:

Thomas 'PointedEars' Lahn said the following on 10/5/2007 7:37 PM:

>Randy Webb wrote:

>>Thomas 'PointedEars' Lahn said the following on 10/5/2007 9:14 AM:
dh**********@gm ail.com wrote:
I do wonder though: Why $? I would like to know, out of curiosity, why
did jQuery use $? There is a reason the variable was used; I just
don't know what it is.
Cluelessness . (That was easy.)
And it is debatable who is the one possessing the "Cluelessne ss".

Not understood.

Try enabling the spell checker in Thunderbird. It might shed some light
on it.

It merely shows that you don't know the word and that it isn't in the
default dictionary of Thunderbird's spell checker.

>>Why it was used is trivial to figure out.

Then you can tell it for sure, yes?

Sure I can.

You can *not*, you are not the author.

It was chosen because of the uniqueness of it and the lack
of use of it on the web.

Logical fallacy: wishful thinking. You can know neither whether or not it
was used on the Web at the time the library was conceived, nor can you know
that supposed uniqueness or supposed no-use at the time was the reason for
choosing it.

What better way to pick a simple single character identifier than one
that wasn't in use?

Logical fallacy: non sequitur.
PointedEars
--
Prototype.js was written by people who don't know javascript for people
who don't know javascript. People who don't know javascript are not
the best source of advice on designing systems that use javascript.
-- Richard Cornford, cljs, <f8************ *******@news.de mon.co.uk>

[Randy Webb]

Thomas 'PointedEars' Lahn said the following on 10/6/2007 7:53 AM:

Randy Webb wrote:

>Thomas 'PointedEars' Lahn said the following on 10/5/2007 7:37 PM:

>>Randy Webb wrote:
Thomas 'PointedEars' Lahn said the following on 10/5/2007 9:14 AM:
dh**********@gm ail.com wrote:
>I do wonder though: Why $? I would like to know, out of curiosity, why
>did jQuery use $? There is a reason the variable was used; I just
>don't know what it is.
Cluelessnes s. (That was easy.)
And it is debatable who is the one possessing the "Cluelessne ss".
Not understood.

Try enabling the spell checker in Thunderbird. It might shed some light
on it.

It merely shows that you don't know the word and that it isn't in the
default dictionary of Thunderbird's spell checker.

<eyerollYou still don't get it. I didn't expect you to though.

>>>Why it was used is trivial to figure out.
Then you can tell it for sure, yes?

Sure I can.

You can *not*, you are not the author.

You need to get out into the real world more often Thomas.

--
Randy
Chance Favors The Prepared Mind
comp.lang.javas cript FAQ - http://jibbering.com/faq/index.html
Javascript Best Practices - http://www.JavascriptToolbox.com/bestpractices/

[Thomas 'PointedEars' Lahn]

dh**********@gm ail.com wrote:

On Oct 13, 2:41 am, Thomas 'PointedEars' Lahn <PointedE...@we b.de>
wrote:

>The code comes from jQuery (1.2.1):

// This may seem like some crazy code, but trust me when I say that this
// is the only cross-browser way to do this. --John
isFunction:func tion( fn ) {
return !!fn && typeof fn != "string" && !fn.nodeName &&
fn.constructor != Array && /function/i.test( fn + "" );
}

jQuery claims to support IE 6.0+, FF 1.5+, Safari 2.0+, Opera 9.0+ (and
calls that "cross-browser" -- OMG). But, if

/function/i.test(fn + "")

would return `true', it is highly unlikely that

typeof fn

would yield "string", so the test

typeof fn != "string"

is unnecessary. Unless, of course, someone who lacks the minimum clue
assumes that strings could be called and so could ever be subject to
isFunction() .

No, it excludes strings.

Which is unnecessary, as strings could never be called, and so should never
be subject to the isFunction() test method.

"function" + "" would return true. This clause prevents that.

But can you name a case where a callable object would evaluate as a string
containing "function" without type conversion?

>Furthermore, if

/function/i.test(fn + "")

would return `true', how could it be that

fn.constructor != Array

var a = Array{function bork(){});

But that assumes that `a' could be called which it cannot be. Hence it
should not be subject to an isFunction() test. An array is not a function.

>couldnotyiel d `true'

Again, I did not write it that way. Please stop using broken software.

and therefore that test would be unnecessary as well?

No.

Yes.

>Needless to say that RegExp.prototyp e.test() already type-converts its
argument to string (see ECMAScript Ed. 3, 15.10.6.3) and so the forced
conversion by concatenation is unnecessary.

That's true, but being explicit is a good thing.

Being explicit would be

/.../.test(String(.. .))

But that would be nonsense as well, as it would decrease efficiency.
Because if the specification algorithm is followed, type conversion
to String would happen *twice* in both cases: first due to the source
code and the second time as step 1 of RegExp.prototyp e.exec().

>And aFunctionobject , being a native object, certainly could have a
user-defined property `nodeName' and still could be called. So that
test makes no sense as well.

Right, so could any of the four examples on my site.

I didn't care about your (Web?) site and I have no intention to do so. If
you have arguments to present, please do it here.

>- False-values could only yield `object', as `null' does, but they wouldnot
type-convert to `true';

- typeof fn == "string" is already excluded (unless one assumes the
improbable case that `typeof' would yield "stringfunction " and the like);

new String()
{toString:funct ion(){return 'function';}}

This is assuming that a String object could be called and so should/could
ever be subject to isFunction().

a = Function();
a.toString = "widget";

What should this accomplish? Overwriting the toString() method with a
string value renders type conversion to string non-functional. And even
if you meant

a = Function();
a.toString = function() { return "widget"; };

`typeof a' still would yield "function". The flaw in the described
algorithm is that it does not use `typeof' first. Because if it did,
many tests would not be necessary and the algorithm as a whole would
be less obscure and less error-prone.

>- fn.constructor != Array could only yield `true' because typeof "function"
would apply;

frames.

I don't see any argument here.

String values do not imply an object's type. Relying on toString is
not safe.

Exactly.
PointedEars

[Thomas 'PointedEars' Lahn]

Randy Webb wrote:

Richard Cornford said the following on 10/14/2007 11:18 AM:

>Randy Webb wrote:

>>Richard Cornford said the following on 10/13/2007 10:28 PM:
<dh********* *@gmail.comwrot e:
typeof fn? nope, not in safari.
Are you certain? Is it really the case that objects that
return 'function' from a typeof operation cannot be
called? Or are you just not expecting them to be callable?
Have you actually tried calling the objects that safari
asserts are functions?
Can I ask you to first define what you mean by "called"
or "callable"?

No more than sticking an ArgumentsList after a reference to the object
(the 'call operator', with or without arguments). That is what I would
consider calling an object, and to be callable that abject should not
throw an exception as a direct result of its being called (though it may
still throw an exception in response to its arguments'' values, as that
would be behaviour passed the point of calling it and so unrelated to
its callability).

That would imply, to me anyway, that Safari (even in Beta form) gets it
right and all other browsers I tested it on get it wrong. Would that be
a correct assumption?

Not at all. With host objects, all bets are off. And as long as objects
that can't be called do not yield `function' or `object', there is no problem.

>>All other Windows based browsers I have report it as 'object'.

Maybe, but that is neither necessarily true of windows based browsers
nor historically common on Mac browsers. Even Mac IE 5 would report
'function' in this context, and on Windows you only have to go back a
few Opera versions to see the same there.

Then Safari is right and IE/FF/Opera are wrong?

It is not a matter of right and wrong.
PointedEars
--
realism: HTML 4.01 Strict
evangelism: XHTML 1.0 Strict
madness: XHTML 1.1 as application/xhtml+xml
-- Bjoern Hoehrmann