Checking if span object(s) exist

[Uzi G.]

Hi,

We have a JSP website intended for viewing with IE 5 (and above)
On a certain jsp page, there are few span objects
(<SPAN ID="name">text </SPAN>), which are created dynamically.

The spans share the same ID, so we are able to reference them as an
array, in the javascript code :
for example:

<SPAN ID="wow">lala</SPAN>
<SPAN ID="wow")kaka</SPAN>

in the JS code:

wow[0].innerHTML = "fafa";
wow[1].innerHTML = "zaza";

It may occur, since these spans are created dynamically by the JSP
page, that on a certain instance of the page, no spans are created.

My question is - how do we know, in the JS code, that no spans of ID
'wow' exist?
We tried several ways:

if (!wow) alert('no wow'); // If there were no spans, this gives a
js error

tried a few other methods which i cant recall of now..
I know of a workaround - to add a 'dummy' span with the 'wow' ID , but
I prefer to know if there is a better way to deal with this.

Thanks in advance,
Uzi

[kaeli]

Re: Checking if span object(s) exist

In article <2b223b69.03100 10723.72e5442f@ posting.google. com>,
antishlook@yaho o.com enlightened us with...[color=blue]
> We tried several ways:
>
> if (!wow) alert('no wow'); // If there were no spans, this gives a
> js error
>[/color]

if (!document.getE lementById("wow ") || document.getEle mentById("wow") ==
null || document.getEle mentById("wow") == "undefined" )
alert ('no wow');

--
-------------------------------------------------
~kaeli~
All I ask for is the chance to prove that money
cannot make me happy.

http://www.ipwebdesign.net/wildAtHeart

http://www.ipwebdesign.net/kaelisSpace

-------------------------------------------------

[Lasse Reichstein Nielsen]

Re: Checking if span object(s) exist

antishlook@yaho o.com (Uzi G.) writes:
[color=blue]
> We have a JSP website intended for viewing with IE 5 (and above)[/color]

I was just about to stop reading here.
[color=blue]
> On a certain jsp page, there are few span objects
> (<SPAN ID="name">text </SPAN>), which are created dynamically.
>
> The spans share the same ID, so we are able to reference them as an
> array, in the javascript code :
> for example:
>
> <SPAN ID="wow">lala</SPAN>
> <SPAN ID="wow")kaka</SPAN>[/color]

I assume the ")" is a type. The generated code is invalid HTML. The ID
attribute must be unique in a page. Anything else is asking for trouble.
.... but if IE allows it, I guess you can ignore correctness.
[color=blue]
> It may occur, since these spans are created dynamically by the JSP
> page, that on a certain instance of the page, no spans are created.
>
> My question is - how do we know, in the JS code, that no spans of ID
> 'wow' exist?[/color]

You are also using the IE-specific way of accessing the named
elements: as a global variables of the same name. That means that
if there are no spans with that id, there is no variable either.
[color=blue]
> We tried several ways:
>
> if (!wow) alert('no wow'); // If there were no spans, this gives a
> js error[/color]

Yes, because there is no global variable called "wow", and it is an error
to access an undeclared variable.
[color=blue]
> tried a few other methods which i cant recall of now..[/color]

Interesting. Almost any other check would work:

if (!document.getE lementById("wow ")) ...
if (!document.all["wow"]) ...
if (!window.wow) ...

(As an interesting side node: If you have two elements with the same id,
and use document.all[id], the returned "array" contains *two* properties
with the same property name (id). Highly spurious!)

/L
--
Lasse Reichstein Nielsen - lrn@hotpop.com
Art D'HTML: <URL:http://www.infimum.dk/HTML/randomArtSplit. html>
'Faith without judgement merely degrades the spirit divine.'

[Grant Wagner]

Re: Checking if span object(s) exist

Lasse Reichstein Nielsen wrote:
[color=blue]
> antishlook@yaho o.com (Uzi G.) writes:
>[color=green]
> > We have a JSP website intended for viewing with IE 5 (and above)[/color]
>
> I was just about to stop reading here.
>[color=green]
> > On a certain jsp page, there are few span objects
> > (<SPAN ID="name">text </SPAN>), which are created dynamically.
> >
> > The spans share the same ID, so we are able to reference them as an
> > array, in the javascript code :
> > for example:
> >
> > <SPAN ID="wow">lala</SPAN>
> > <SPAN ID="wow")kaka</SPAN>[/color]
>
> I assume the ")" is a type. The generated code is invalid HTML. The ID
> attribute must be unique in a page. Anything else is asking for trouble.
> ... but if IE allows it, I guess you can ignore correctness.
>[color=green]
> > It may occur, since these spans are created dynamically by the JSP
> > page, that on a certain instance of the page, no spans are created.
> >
> > My question is - how do we know, in the JS code, that no spans of ID
> > 'wow' exist?[/color]
>
> You are also using the IE-specific way of accessing the named
> elements: as a global variables of the same name. That means that
> if there are no spans with that id, there is no variable either.
>[color=green]
> > We tried several ways:
> >
> > if (!wow) alert('no wow'); // If there were no spans, this gives a
> > js error[/color]
>
> Yes, because there is no global variable called "wow", and it is an error
> to access an undeclared variable.[/color]

Use the "typeof" operator to test for the existance of a variable/object
property:

if (typeof wow == 'undefined') {
alert('no wow');
}

But as was pointed out earlier, you shouldn't have multiple elements on a
page with the same id, you'd be much better off using:

<span id="wow1">...</span>
<span id="wow2">...</span>
<!-- etc -->

--
| Grant Wagner <gwagner@agrico reunited.com>

* Client-side Javascript and Netscape 4 DOM Reference available at:
*

http://devedge.netscape.com/library/manuals/2000/javascript/1.3/reference/frames.html

* Internet Explorer DOM Reference available at:
*

http://msdn.microsoft.com/workshop/author/dhtml/reference/dhtml_reference_entry.asp

* Netscape 6/7 DOM Reference available at:
* http://www.mozilla.org/docs/dom/domref/
* Tips for upgrading JavaScript for Netscape 7 / Mozilla
* http://www.mozilla.org/docs/web-deve...upgrade_2.html

[W d'Anjos]

Re: Checking if span object(s) exist

You can use:

if (!document.all. wow) alert('no wow');

I hope this helps.

-Wagner

[Lasse Reichstein Nielsen]

Re: Checking if span object(s) exist

Grant Wagner <gwagner@agrico reunited.com> writes:
[color=blue]
> Use the "typeof" operator to test for the existance of a variable/object
> property:
>
> if (typeof wow == 'undefined') {
> alert('no wow');
> }[/color]

Interesting. I didn't know that "typeof" allowed undeclared variables,
but reading the ECMAScript specification, it does work as you say.
Thanks :)
/L
--
Lasse Reichstein Nielsen - lrn@hotpop.com
Art D'HTML: <URL:http://www.infimum.dk/HTML/randomArtSplit. html>
'Faith without judgement merely degrades the spirit divine.'