Exception when creating another object

Hi,

on writing some nice javascript classes, 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.

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.

Thanks a lot for any suggestions!

Greetings
Erik

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>