How to assign Javascript return value in c# Code behind Variable

Question

How to assign the javascript return value to c# code behind variable, while the page load. I am trying to do this. Please see the below example. I want the exact result like this.

Note : I already posted a question like this,but that is meaning less.

Javascript:
<script>
function GetValue() {
return 10;
}
</script>

C#.NET

protected void Page_Load(object sender, EventArgs e)
{
int Data
ClientScript.RegisterStartupScript(this.GetType(), "GetData", "a=GetValue();alert(a)", true);
Data=a;//a is Javascript Variable
}

this really is the same question you are asking previously... — ljs.dev
– ljs.dev, Commented Sep 17, 2013 at 4:17
possible duplicate of Get onload hidden field value using c# — ljs.dev
– ljs.dev, Commented Sep 17, 2013 at 4:17
Your flow is incorrect. You can not get value in Data in Page_Load. Reason is ClientScript.RegisterStartupScript will execute Javascript after Page_Load event complete. So you can not set value like this. What is your purpose to store value? Remember you can store this value on client side with use of javascript or jquery. — Harshil Raval
– Harshil Raval, Commented Sep 17, 2013 at 4:41

Adam Carr · Accepted Answer · 2016-01-22 12:36:36Z

1

What you are asking is impossible. The page load is part of the aspnet webforms request/response lifecycle. This determines what page content is generated.

The JavaScript will run on the client browser, after the page content has been generated. So there is no way to use any server side methods to get your value on page generation.

You can either pass the value as a querystring, post back a value or use a web service.

answered Jan 22, 2016 at 12:36

Adam Carr

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Comments

Saurabh · Accepted Answer · 2013-09-17 04:18:45Z

0

Take a hidden field or Label in the form. Assign return value to the Hidden form with document.getElementById('ID').value = 10;
Call this function from CodeBehind and get the value of Hiddnefield in the code behind.
I hope this helps.

answered Sep 17, 2013 at 4:18

Saurabh

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Comments

Vishweshwar Kapse · Accepted Answer · 2013-09-17 04:46:21Z

0

To be more clear do something like this...

In your HTML define a tag like this

<asp:HiddenField ID="hfData" runat="server" />

And then write a javascript function that looks like this

 function putData()
     {
        document.getElementById('hfData').value = 10;
     }

and then on your page_load do something like this

 protected void Page_Load(object sender, EventArgs e)
   {
     int Data = hfData.Value;
   }

this should get youur client side data on server side for further processing

answered Sep 17, 2013 at 4:46

Vishweshwar Kapse

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1 Comment

Harshil Raval Over a year ago

It will not work, as javascript function will execute after page load event complete. So, on first time page load hiddenfield value remain always null.

Tommy · Accepted Answer · 2015-12-22 02:18:55Z

0

You can store the JavaScript value in hidden variable then access this value from the code behind.

edited Dec 22, 2015 at 2:18

Tommy

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answered Sep 17, 2013 at 6:01

SANDEEP

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