<div>
The last option is actually not what I want, because it requires an iteration of all fields of the form, which is expensive. &nbsp;The 1st is good for me.
</div>


The last option is actually not what I want, because it requires an iteration of all fields of the form, which is expensive.  The 1st is good for me.

<div>
Thanks,<br />
<br />
But how many fields do you have? It would take at least 50+ fields to make a difference as far as I have seen.<br />
<br />
Michel
</div>


Thanks,

But how many fields do you have? It would take at least 50+ fields to make a difference as far as I have seen.

Michel

<div>
I was just having this problem myself, and I thought this may help:<br />
<br />
//JavaScript 1.3 added the if(x==undefined) capability, but previous versions require a workaround<br />
function isDefined(o) {<br />
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;varToStr=eval(&quot;' &quot;+o+&quot;'&quot;);<br />
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;if (varToStr==&quot; undefined&quot;) {<br />
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;return false;<br />
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;} else {<br />
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;return true;<br />
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;}<br />
}<br />

</div>


I was just having this problem myself, and I thought this may help:

//JavaScript 1.3 added the if(x==undefined) capability, but previous versions require a workaround
function isDefined(o) {
      varToStr=eval("' "+o+"'");
      if (varToStr==" undefined") {
            return false;
      } else {
            return true;
      }
}


<div>
And also added === that will test for null<br />
<br />
Michel
</div>


And also added === that will test for null

Michel

<div>
<div class="content wysiwyg-content">
In javascript, how do I know whether a particular object exists or not?<br />
<br />
For example, suppose f is a form,<br />
<br />
var field = eval(&quot;f.&quot; + &quot;address&quot;);<br />
field.value = &quot;USA&quot;;<br />
<br />
This code is fine if there is a field named &quot;address&quot; in the form, but if such<br />
a field does not exist (since the javascript function will be a common one)<br />
how can I tell that field is undefined and therefore skip the assignment<br />
which will cause an error?<br />
<br />
Must work for IE and Netscape.<br />
<br />

</div>
</div>


In javascript, how do I know whether a particular object exists or not?

For example, suppose f is a form,

var field = eval("f." + "address");
field.value = "USA";

This code is fine if there is a field named "address" in the form, but if such
a field does not exist (since the javascript function will be a common one)
how can I tell that field is undefined and therefore skip the assignment
which will cause an error?

Must work for IE and Netscape.



check whether an object exists

JavaScript is a dynamic, object-based language commonly used for client-side scripting in web browsers. Recently, server side JavaScript frameworks have also emerged. JavaScript runs on nearly every operating system and  in almost every mainstream web browser.