Property in prototype

[Robert]

Hi,

I would like to determine if a property is available in an Event prototype.
I tried doing this using:

if (Event.prototype.srcElement)

but I got an "Illegal operation on WrappedNative prototype object"
exception. Is there anyway to see if it already has been defined.

One other question I have is if the __defineGetter__ method is part of
some Javascript/ECMA Script version or if it is Mozilla proprietary.

Thanks!
Robert

 

[Martin Honnen]

One other question I have is if the __defineGetter__ method is part of
some Javascript/ECMA Script version or if it is Mozilla proprietary.

__defineGetter__ is implemented in the Spidermonkey engine that
implements JavaScript 1.5. That engine is used in Mozilla. So one could
say that __defineGetter__ is part of JavaScript 1.5 depending of what is
considered to define that version.
__defineGetter__ is not part of any existing ECMAScript specification
version.

 

[Martin Honnen]

Robert wrote:

I would like to determine if a property is available in an Event prototype.
I tried doing this using:

if (Event.prototype.srcElement)

but I got an "Illegal operation on WrappedNative prototype object"
exception. Is there anyway to see if it already has been defined.

Is that Firefox 1.03? Then you are probably running into a messy bug, a
workaround is described here:

<http://developer-test.mozilla.org/en/docs/Working_around_the_Firefox_1.0.3_DHTML_regression>

 

[Robert]

Robert wrote:




Is that Firefox 1.03? Then you are probably running into a messy bug, a
workaround is described here:

No I use Firefox 1.04
Are you implying that Event.prototype.srcElement should work?

 

[Martin Honnen]

No I use Firefox 1.04
Are you implying that Event.prototype.srcElement should work?

I don't think it should give an error, of course natively srcElement is
not part of the Mozilla DOM so you would need to add your own script to
add that property.

What is the user agent string of Firefox 1.04, I have tested here with
Mozilla 1.7.7 (Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.7.7)
Gecko/20050414) and it does not give an error when accessing
Event.prototype.srcElement
but simply gives undefined.

 

[Robert]

I don't think it should give an error, of course natively srcElement is
not part of the Mozilla DOM so you would need to add your own script to
add that property.

Yes of course. I was expecting it to return undefined.

What is the user agent string of Firefox 1.04, I have tested here with
Mozilla 1.7.7 (Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.7.7)
Gecko/20050414) and it does not give an error when accessing
Event.prototype.srcElement
but simply gives undefined.

Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.7.8) Gecko/20050511
Firefox/1.0.4

It seems mine is newer... So probably a regression. I will try to see if
they have a newer version available where they have fixed it again.

 

[Martin Honnen]

Robert wrote:

Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.7.8) Gecko/20050511
Firefox/1.0.4

It seems mine is newer... So probably a regression. I will try to see if
they have a newer version available where they have fixed it again.

That is odd, I have now tried with Mozilla 1.7.8
Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.7.8) Gecko/20050511
and do not get any error either.

 

[Robert]

Robert wrote:




That is odd, I have now tried with Mozilla 1.7.8
Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.7.8) Gecko/20050511
and do not get any error either.

A restart has solved the problem.
Maybe the weather was too warm for the computer today
Anyway it works now
srcElement property being added if it was not already defined.

Thanks for trying to help me!

 

[Robert]

A restart has solved the problem.

I spoke too soon!
The problem only occurs after I have defined the srcElement.

So if I have executed the following code:

Event.prototype.__defineGetter__("srcElement", function()
{
var node = this.target;
while (node.nodeType != 1)
node = node.parentNode;
return node;
});

And later I do

if (Event.prototype.srcElement)

I will get the exception

 

[Yann-Erwan Perio]

Robert wrote:

Hi,

The problem only occurs after I have defined the srcElement.

So if I have executed the following code:

Event.prototype.__defineGetter__("srcElement", function()
{
var node = this.target;
while (node.nodeType != 1)
node = node.parentNode;
return node;
});

And later I do

if (Event.prototype.srcElement)

I will get the exception

That's quite normal, you've actually just defined a getter for
Event.prototype, and then you *call* it in the "if" structure while you
should just check its existence; as a result, in the call, "this" refers
to the prototype itself, not any event, and calling the getter defined
for "target" in such a context makes it fail.

Be more defensive, with the srcElement getter

Event.prototype.__defineGetter__(
"srcElement",
function() {
var node=null;
if(this.constructor==Event) {
node = this.target;
while (node && node.nodeType != 1)
node = node.parentNode;
}
return node;
}
);

and with the way you infer the existence of a property

function isUndefined(obj, prop){
var isUndefined=true;
if(obj.__lookupGetter__){
if(typeof obj.__lookupGetter__(prop)!="undefined") {
isUndefined=false;
}
}
if(isUndefined) {
isUndefined=(typeof obj[prop]=="undefined");
}
return isUndefined;
}


HTH,
Yep.

 

[Robert]

Robert wrote:

Hi,




That's quite normal, you've actually just defined a getter for
Event.prototype, and then you *call* it in the "if" structure while you
should just check its existence; as a result, in the call, "this" refers
to the prototype itself, not any event, and calling the getter defined
for "target" in such a context makes it fail.

Ahhhhhhhh yes of course!
Thank you. I understand it now and your examples were helpful too.