null attribute

[TJS]

how to check for null attribute in form input field using IE

this does not work in IE

var curr_id = tablecells[i].getAttribute(' name');
if (curr_id != null){
....
}

[Mick White]

Re: null attribute

TJS wrote:[color=blue]
> how to check for null attribute in form input field using IE
>
> this does not work in IE
>
> var curr_id = tablecells[i].getAttribute(' name');
> if (curr_id != null){
> ...
> }
>
>[/color]

if(var curr_id = tablecells[i].getAttribute(' name'))

Mick

[TJS]

Re: null attribute

that compares values but doesn't give me the desired result and doesn't
check to see if it's null


"Mick White" <mwhite13BOGUS@ rochester.rr.co m> wrote in message
news:Vytod.1114 2$1u.3531@twist er.nyroc.rr.com ...[color=blue]
> TJS wrote:[color=green]
>> how to check for null attribute in form input field using IE
>>
>> this does not work in IE
>>
>> var curr_id = tablecells[i].getAttribute(' name');
>> if (curr_id != null){
>> ...
>> }[/color]
>
> if(var curr_id = tablecells[i].getAttribute(' name'))
>
> Mick[/color]

[Rob B]

Re: null attribute



Are you simply validating a non-empty field? Text controls have .value
properties, 'empty' ones contain the null (empty) string, not the null
value.

var curr_id = tablecells[i].getAttribute(' value');
if (/^\s*$/.test(curr_id)) {
....
}

The regex catches all-space entries as well as empty ones.

Not clear what that 'tablecells' array contains...


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[Fred Oz]

Re: null attribute

TJS wrote:[color=blue]
> that compares values but doesn't give me the desired result and doesn't
> check to see if it's null[/color]

var x = null; // x is set to null, (x == null) is true.
var x; // x is undefined, (x == null) is true.
var x; // x is undefined, (x === null) is false.
var x = ''; // x is empty string, (x == null) is false.
x; // x is undefined, javascript error.

Fred.

[Michael Winter]

Re: null attribute

On Mon, 22 Nov 2004 17:07:35 -0800, TJS <nospam@here.co m> wrote:

[Corrected top-post]

Please don't do that in future.
[color=blue]
> "Mick White" <mwhite13BOGUS@ rochester.rr.co m> wrote in message
> news:Vytod.1114 2$1u.3531@twist er.nyroc.rr.com ...[/color]

[snip]
[color=blue][color=green]
>> if(var curr_id = tablecells[i].getAttribute(' name'))[/color][/color]

That's a syntax error. The var statement cannot appear in an expression.

var curr_id = tablecells[i].getAttribute(' name');
if(curr_id) {
// curr_id contains the name
}

or

var curr_id
if((curr_id = tablecells[i].getAttribute(' name')) {
// curr_id contains the name
}
[color=blue]
> that compares values but doesn't give me the desired result and doesn't
> check to see if it's null[/color]

Really, checking for null is incorrect as Element.getAttr ibute cannot
return null, only a string. However, Microsoft (as usual) have cocked
things up, allow all manner of types to be returned.

Mick's suggestion was the right approach, except for the syntax error.
When you evaluate an expression within an if statement, the result of that
evaluation is coerced into a boolean. Different types are coerced in
different ways.

Boolean -> (no conversion)
Null -> false
Number -> false if plus/minus zero (+/-0) or NaN, true otherwise
Object -> true
String -> false if empty string (''), true otherwise
Undefined -> false

So as you can see, if curr_id was null, it would evaluate to false and the
block would not be executed.

There is another reason which I briefly mentioned earlier which makes
Mick's suggestion the right one: Element.getAttr ibute is not supposed to
return null, only a string. This would mean that the comparison in
conforming browsers would be

if(<string> != null) {

which would *always* be true, even if the string was empty, which is
probably not what you want.

Anyway, the sensible thing to do (assuming you're using HTML, not XML) is
to avoid Element.getAttr ibute completely. You can achieve the same with

var curr_id = tablecells[i].name;

which will always succeed (again, only if you're using HTML).

By the way:

1) Table cells cannot have name attributes.
2) The identifier, curr_id, is a misnomer. Wouldn't curr_name be
more appropriate, or even better

var curr_id = tablecells[i].id;

Mike

--
Michael Winter
Replace ".invalid" with ".uk" to reply by e-mail.

[TJS]

Re: null attribute

great response, thank you........