Undefined and null in Javascript

[Oleg Konovalov]

Hi,

I am working on a web application which among other things uses DHTML, Java
and Javascript.
It populates web page based on the contents of the database (resultset),
and next to each row there is a checkbox (v1) allowing to select that row
for changes (e.g. delete, update, etc.)
So we are creating an array of checkbox, correct ?
Of course I have to check whether any of these checkboxes exist and if any
of them got selected (checked)
using Javascript before allowing any DB operation in Java.

Now it becomes strange.
I have noticed that if there is 1 row [i.e. 1 checkbox v1], that function
always shows warning and returns false:
function isAnySelected(c heckbox) //check if at least one checkbox is
selected
{
for(i=0; i<checkbox.leng th; i++) {
if(checkbox[i].checked) {
return true;
}
alert("You must choose at least one record.");
return false;
}
Why ? I call it as: onClick="if(! isAnySelected(v 1)) return false;"
I tried to fix that error, and noticed that in the case of a single row
checkbox.length is "undefined" .
So I modified that function into:

function isAnySelected(c heckbox) //OK: check if at least one checkbox is
selected
{
if(checkbox.len gth = "undefined" ) { // with single '=' !!!
if(checkbox.che cked) {
return true;
}
} else {
for(i=0; i<checkbox.leng th; i++) {
if(checkbox[i].checked) {
return true;
}
}
}
alert("You must choose at least one record.");
return false;
}

What I can't understand here is why that function works only when there is a
single '=' here:
if(checkbox.len gth = "undefined" )... ???
Checking for null produces Javascript errors or does nothing.

And how can I make it work if there are 0 rows [and thus 0 instances of
checkbox v1 ?]

Thank you in advance,
Oleg.

[VK]

1) JavaScript runtime error: "v1" is undefined is coming from the

function call:
if (! isAnySelected(v 1)) return false;
not from inside the function.
Are you sure that this check can fix that ?

Yes, I am: unless v1 was not declared anywhere in your program before
if (! isAnySelected(v 1)) return false
"declared" would mean that somewhere in your program you have
var v1;
or
var v1 = something;
Also I see a strong "Java school" in this line (the famous
"truthulize r" joke about you, guys :-)
return isAnySelected(v 1)
does the same as
if (! isAnySelected(v 1)) return false
else return true
as you may guess

If v1 declared but has undefined value then inside the function you
trying to access the property of undefined : undefined.lengt h and it
trigs the error. So first you check if v1 is not undefined and only
then you try to access a property of it. You may move the check level
up if you want (at the moment of the function call):
if (typeof v1 != 'undefined') { return isAnySelected(v 1); }

2) if (typeof check == 'object') {...
Hmm, do you mean that if that collection is not empty, it's an 'object' ?
Never thought of it that way.

That depends on how are getting v1. Really: the whole HTTP page is
needed to see what and how are you doing (brought to the minimum case
if possible).

[VK]

VK wrote:

if (typeof v1 != 'undefined') { return isAnySelected(v 1); }

Better:

return (typeof v1 != 'undefined') ? isAnySelected(v 1) : false;
// otherwise with undefined v1 there will be no explicit
// return value which is dangerous.
// still posting the entire working page is more than
// suggested.

[Oleg Konovalov]

VK,

It would be very difficult to show the whole XSL page with all HTML &
Javascript,
it is a part of old large Cocoon/XSLT/Java application.

But the part related to v1 checkbox would be :

for each DB row (become XML nodes) - we are looping through them:
<input name="v1" type="checkbox" >
<xsl:attribut e name='value'><x sl:value-of
select='$therow/id'/></xsl:attribute>
</input>
--the value=therow/id to identify the row for operation on it
[like delete or modify or compare or display all detailed values]
So if the query returned no rows, there will be no instances of checkbox on
the page.

Hope it answers your question.

I will try your original and modified solutions tomorrow and let you know.

Thank you,
Oleg.
"VK" <sc**********@y ahoo.comwrote in message
news:11******** **************@ k70g2000cwa.goo glegroups.com.. .

>
VK wrote:

> if (typeof v1 != 'undefined') { return isAnySelected(v 1); }

Better:

return (typeof v1 != 'undefined') ? isAnySelected(v 1) : false;
// otherwise with undefined v1 there will be no explicit
// return value which is dangerous.
// still posting the entire working page is more than
// suggested.

[VK]

Oleg Konovalov wrote:

But the part related to v1 checkbox would be :

for each DB row (become XML nodes) - we are looping through them:
<input name="v1" type="checkbox" >
<xsl:attribut e name='value'><x sl:value-of
select='$therow/id'/></xsl:attribute>
</input>
--the value=therow/id to identify the row for operation on it
[like delete or modify or compare or display all detailed values]
So if the query returned no rows, there will be no instances of checkbox on
the page.

This way the resulting HTML output will be like
<input type="checkbox" name="v1">Recor d 1</input>
<br>
<input type="checkbox" name="v1">Recor d 2</input>
<br>
<input type="checkbox" name="v1">Recor d 3</input>
(I'm sure you are using table rows instead, but for a short idea is
enough)

This way the suggested check could be (see comments inside):

<html>
<head>
<title>Checkbox es</title>
<meta http-equiv="Content-Type"
content="text/html; charset=iso-8859-1">

<script type="text/javascript">

function validate(refFor m) {
var ret = false;

// ... other form validations ...

// Please note that "v1" is a string literal
// (form element name), not an object:
ret = isAnySelected(r efForm.elements["v1"]);

return ret;
}
function isAnySelected(c heck) {
var ret = false;

// if at least one matching element found:
if (typeof check != 'undefined') {

// if several matching elements founds:
if (check.length) {
// intermediary var to speed up the loop:
var len = check.length;
for (var i=0; i<len; ++i) {
// if the element has boolean field "checked"
// and this field is set to true:
if ((typeof check[i].checked == 'boolean')
&& (check[i].checked)) {
ret = true;
break;
}
}
}

// if only one matching element found
// and the element has boolean field "checked"
// and this field is set to true:
else if (typeof check.checked == 'boolean') {
ret = check.checked;
}

// Else do nothing, just balance if-else clause:
else {
/*NOP*/
}

}

return ret;
}
</script>

</head>

<body>
<form method="POST" action="" onsubmit="retur n validate(this)" >
<fieldset>
<input type="checkbox" name="v1">Recor d 1</input>
<br>
<input type="checkbox" name="v1">Recor d 2</input>
<br>
<input type="checkbox" name="v1">Recor d 3</input>
<br>
<input type="submit">
</fieldset>
</form>
</body>
</html>