Assign a field from javascript and retrieve it from CodeBehind

Question

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I'm just doing :

Javascript:

JavaScript

function assign(){
 var sHidVar = 'something';
 document.getElementById('<%=hdnPage.ClientID%>') = sHidVar ;
 alert(document.getElementById('<%=hdnPage.ClientID%>'));
}

ASPX

ASP.NET

...
 <asp:HiddenField ID=hdnPage runat=server  />
...

Here is the problem when I do this:
ASPX :

HTML

<a href=#  önclick="Javascript:assign();">Test</a>

it runs fine, the variable is assigned and I can access from CodeBehind by:

C#

string s = hdnPage.Value;

but, to run this function on page load like :

C#

protected void Page_Load(object sender, EventArgs e)
...
ClientScript.RegisterClientScriptBlock(this.GetType(), "assign", "assign();", true);
..
}

it gives an error, saying document.getElementById(...) is not an object

how else can I call the function on page load, of is there something wrong with the function

PS: Also tried the

JavaScript

$('<%=hdnPage.ClientID%>')

, doesn't work

Posted 30-Oct-12 23:26pm

saud_a_k

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2 solutions

Solution 1

Place your JavaScript function before just before the end of the tag and test.

Posted 31-Oct-12 0:24am

Shreekanth Gaanji

Comments

saud_a_k 31-Oct-12 8:14am

I use a MasterPage , I need to place the js in the content

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bbirajdar · Accepted Answer · 2012-10-31T00:43:00

Solution 2

You cannot call the javascript function on server side page_load. For that you need to user javascript window.onload event like this

JavaScript

window.onload=function assign(){
 var sHidVar = 'something';
 document.getElementById('<%=hdnPage.ClientID%>') = sHidVar ;
 alert(document.getElementById('<%=hdnPage.ClientID%>'));
}

Posted 31-Oct-12 0:43am

bbirajdar

Comments

saud_a_k 31-Oct-12 7:47am

Thanx, that was simple
But still can't you call a jscript fun. from C# ?

bbirajdar 31-Oct-12 8:37am

Because javascript is executed on client side and server side script is executed on server side.... You should read more on client-server processing model.

saud_a_k 31-Oct-12 8:47am

Yes I understand that,
of course there is the webmethod way that uses static functions,
but then how are you supposed to use ClientScript.RegisterClientScriptBlock etc.. ??

bbirajdar 31-Oct-12 9:00am

No.. WebMethods are used for different purpose