Strange problem with hidden variables being found 'null' by Javascript

harrierdh 0 Junior Poster in Training · 2010-02-18T22:48:54+00:00

What you posted was asp code not html. My suggestion is that you bring up the web page and do a View Source in your browser. The javascript is probably right. Your fields are probably empty when they hit the browser. Which would mean you have an asp error not a javascript error.

cmouli 0 Newbie Poster · 2010-02-19T16:13:19+00:00

from view state:

<html>
<head>
<script language="javascript">
function Print() {
alert(document.getElementById('hdnMyHidden'));
alert(document.getElementById('hdnMyHidden').value);

var strmyCodes = document.getElementById("hdnmyCode").value;
var strmyDesc = document.Form1.hdnmyCode.value;
alert(strmyCodes);
alert(strmyDesc);

alert('hello from asp.net');
} 

</script>

</head>
<body scroll="no">
<form id="Form1" method="post" runat="server">
<input type="hidden" name="__EVENTTARGET" id="__EVENTTARGET" value="" />
<input type="hidden" name="__EVENTARGUMENT" id="__EVENTARGUMENT" value="" />
<input type="hidden" name="__LASTFOCUS" id="__LASTFOCUS" value="" />

<script type="text/javascript">
<!--
var theForm = document.forms['Form1'];
if (!theForm) {
    theForm = document.Form1;
}
function __doPostBack(eventTarget, eventArgument) {
    if (!theForm.onsubmit || (theForm.onsubmit() != false)) {
        theForm.__EVENTTARGET.value = eventTarget;
        theForm.__EVENTARGUMENT.value = eventArgument;
        theForm.submit();
    }
}
// -->
</script>


<script language=JavaScript type=text/javascript> 
alert('hello from vb.net');
Print();
 </script>
<input id="hdnmyCode" type="hidden" runat="server" name="hdnmyCode" value="111">
<input id="hdnMyHidden" type="hidden" name="hdnMyHidden"  value="hi 123"> 
<input id="btn" type="submit" name="save" onclick="javascript: Print()">

</form>
</body>
</html>

harrierdh 0 Junior Poster in Training · 2010-02-19T23:07:24+00:00

Well I do see a problem. Some of your javascript is in the body and is running before your input fields are loaded.

Here your javascript call to Print() is running before the input fields are loaded.

cmouli 0 Newbie Poster · 2010-03-03T13:37:50+00:00

As I said it was a strange problem and yes it was indeed.

I finally took a brand new ASP.NET page (.aspx) and kept adding html and javascript in bits and pieces from the original. So did I add the server code in the (aspx.vb) file. At a point, I was facing the same problem, with the hidden controls again reporting null.

In the code behind (vb), I was writing RegisterClientScriptBlock instead of RegisterStartupScript, to register and call this piece of Javascript. Although, the original copy of code was using RegisterStartupScript, which I had changed to RegisterClientScriptBlock for investigation.

But, at the end, with the new files, all same old code (HTML & server code) and even the original RegisterStartupScript, it worked.

I really dont know whats the mystery behind. Simply, Old Wine in a New Bottle!