Exception when creating another object - Javascript

Erik Wegner wrote:
> on writing some nice javascript classes,

You don't. You are dealing with programming languages that support
"only" prototype-based inheritance.

> I stumble upon the following error, which I find no hint for:
>
> First, there is an object:
>
> function pic(bname, x, y) {
> this.x = x;
> this.y = y;
> this.objektid = bname;
>
> this.positionXY = function(posx, posy) {
> // some code
> }
>
> this.move = function() {
> // some code
> }
> }
>
> When loading my sample page, I create 7 objects by calling
> apic = new pic("examplename", 150, 150);
> which works fine.

However, constructor identifiers should start with a capital letter to
distinguish them from other methods easily.

> After a while, I click on a hyperlink, which calls a javascript
> function. Within this function, I repeat the creation step exactly
> (copy&paste) as above, but now Firefox presents the error message:
>
> Fehler: uncaught exception: [Exception... "Cannot convert
> WrappedNative to function" nsresult: "0x8057000d
> (NS_ERROR_XPC_CANT_CONVERT_WN_TO_FUN)" location: "JS frame ::
> http://localhost/~user/project/js/lib.js :: anonymous :: line 255"
> data: no]
>
> Line 255 looks like
> apic = new pic("examplename", 150, 150);
> and gets already called 7 times before my eightth call which then
> fails. I have no idea where to look for a solution.

A quick Google search for the error code NS_ERROR_XPC_CANT_CONVERT_WN_TO_FUN
would have revealed (as your notion of classes above already indicated) that
your problem is the infamous Prototype library. Stop using that and all of
its deluded offsprings (like Script.aculo.us) and many of your problems will
go away.


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, <f806at$ail$1$8300dec7@news.demon.co.uk>

Thomas 'PointedEars' Lahn said the following on 8/12/2007 12:09 PM:
> Erik Wegner wrote:
>> on writing some nice javascript classes,
>
> You don't. You are dealing with programming languages that support
> "only" prototype-based inheritance.

Which is totally irrelevant to the question and saying a million times
that JS doesn't have "classes" or "Associative Arrays" won't change the
fact that people call them "classes" and "Associative Arrays". Let them
call them what they want and get used to it because it isn't going to
change.

<snip>

>> When loading my sample page, I create 7 objects by calling
>> apic = new pic("examplename", 150, 150);
>> which works fine.
>
> However, constructor identifiers should start with a capital letter to
> distinguish them from other methods easily.

You can name and capitalize them however you want and it won't make a
hill of beans difference. What and how you name functions (as long as it
doesn't clash with a built in function/object name) is totally up to the
programmer and what they choose to use.

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

Erik Wegner wrote:

> Fehler: uncaught exception: [Exception... "Cannot convert
> WrappedNative to function" nsresult: "0x8057000d
> (NS_ERROR_XPC_CANT_CONVERT_WN_TO_FUN)" location: "JS frame ::
> http://localhost/~user/project/js/lib.js :: anonymous :: line 255"
> data: no]
>
> Line 255 looks like
> apic = new pic("examplename", 150, 150);
> and gets already called 7 times before my eightth call which then
> fails. I have no idea where to look for a solution.

Do you have an element in the page with id="pic"? And is that HTML
document rendered in quirks mode?

--

Martin Honnen
http://JavaScript.FAQTs.com/

Martin Honnen wrote:

> Do you have an element in the page with id="pic"? And is that HTML
> document rendered in quirks mode?

Could also be an element with name="id" (e.g <img name="pic" ...>). And
quirks mode is not relevent, you are probably using an event handler
e.g. <a onclick="apic = new pic(...)"> and in such an event handler the
document object and with that document.pic sits in the scope chain so
your code is not accessing the function named pic but rather an element
object named pic.


--

Martin Honnen
http://JavaScript.FAQTs.com/

On Sun, 12 Aug 2007 at 18:09:27, in comp.lang.javascript, Thomas
'PointedEars' Lahn wrote:

<snip>
>However, constructor identifiers should start with a capital letter to
>distinguish them from other methods easily.
<snip>

It's class names that should start with a capital letter. But javascript
doesn't have classes ...

John
--
John Harris

John G Harris wrote:
> [...] Thomas 'PointedEars' Lahn wrote:
>> However, constructor identifiers should start with a capital letter to
>> distinguish them from other methods easily.
>
> It's class names that should start with a capital letter.

That is also true. It does not invalidate my statement though.

> But javascript doesn't have classes ...

That is only partially true.


PointedEars
--
var bugRiddenCrashPronePieceOfJunk = (
navigator.userAgent.indexOf('MSIE 5') != -1
&& navigator.userAgent.indexOf('Mac') != -1
) // Plone, register_function.js:16

Thomas 'PointedEars' Lahn said the following on 8/13/2007 5:06 PM:
> John G Harris wrote:
>> [...] Thomas 'PointedEars' Lahn wrote:
>>> However, constructor identifiers should start with a capital letter to
>>> distinguish them from other methods easily.
>> It's class names that should start with a capital letter.
>
> That is also true. It does not invalidate my statement though.

Your statement wasn't true to start with so it didn't need invalidating.

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