object.length undefined

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June 28th, 2004, 07:22 PM

rxsid

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object.length undefined

Hi all,

I've got a form (called form1) and a checkbox element (called listing).

When my js function is executed on click, the following elemLength displays 2 if 2 of the listing checkboxes are checked, or 5 if 5 are checked, etc.

var elemLength = form1.listing.length;

However...if only 1 listing checkbox is available to check and it's checked, elemLength returns undefined. Why? Why wouldn't it return 1?

June 28th, 2004, 07:28 PM

jacktasia

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post the code or a link to the page please.

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June 28th, 2004, 07:37 PM

rxsid

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The listing checkbox is generated via a php db query and can be 1 or more checkboxes....all named listing with some different value.

[javascript]
function doCheck() {
var elemLength = form1.listing.length;
alert(elemLength);
}
[/javascript]

PHP Code:


		
			
echo "<input type=checkbox name=listing value="$someID">";

[html]
<input type="button" value="Do Check" onClick="return doCheck();">
[/html]

if only 1 checkbox is generated, and it is checked...the elemLength var is undefined....even though there is one .listing that is checked. I can do an alert (form1.listing.value) and it does show the $someID.
if 2+ checkboxes are generated, and 2+ of them are checked...elemLength show's it's length (ie how many are checked).

June 28th, 2004, 08:02 PM

jacktasia

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i think it's because the object hasn't been turned into an array unless there is more than one, so .length isn't of vaild usage...why can't you just test and see if it's undefined and if it is then you know it's one, like this:

Code:

var elemLength =document.form1.listing.length;
if (elemLength==undefined) {
	elemLength=1;
}

Last edited by jacktasia : June 28th, 2004 at 08:07 PM.

June 28th, 2004, 08:07 PM

rxsid

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that will check for undefined, but here's what i have later in the code that doesn't work:

Code:

for (var i = 0; i<elemLength; i++) {
    if (form1.listing[i].checked) {
        //do some work here.   
    }
}

if the 1 checkbox scenario is present, the above code give me a run time error.

June 28th, 2004, 08:13 PM

jacktasia

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well, you of course would have to do something like this...

Code:

if (elemLength==undefined) {
	elemLength=1;
	if (document.form1.listing.checked) {
		// we know the one and only is checked
	}
} else {
	for (var i = 0; i<elemLength; i++) {
		if (form1.listing[i].checked) {
			//do some work here.
		}
	}
}

June 28th, 2004, 08:20 PM

rxsid

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bingo!

that did the trick.

thanks jacktasia!!