Return Value from Javascript to Server Side in ASP.NET

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By  kirtan007   On  04 Jul 2010 22:07:04
Tag : ASP.NET , Miscellaneous
This article will teach you how to retrieve JavaScript functions Return Value to Code Behind
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Some time it's necessary to send a JavaScript function's return value to server-side. For example, we are able to show a Confirm Dialog using Page.RegisterClientScriptBlock() but after we are cannot determine which button a user have pressed on the JavaScript Confirm Dialog. This article will teach you about how to get values in JavaScript from a client-side to server-side such as find out what button a user has clicked on a ConfirmDialog.


Basic Knowledge of JavaScript,C#.

Technology c# 2.0/3.5


Suppose we want to show a confirm dialog when user selects some item in a Dropdownlist and we want to know which Button user have pressed on the Confirm Dialog. Means we want to know if he has pressed "Ok" button or "Cancel" button in our code on server-side.

To get JavaScript values in the code-behind, we need Hidden Input Control, whose runat attribute we will set to  runat="Server" so that it can be accessible in code-behind. It will work as an intermediately to pass the value from client-side to server-side.

Below, I have highlighted two parts - One is Script in <head> part of the code it contain Function ConfirmIt() .

That will be executed when a user select an item in the DropDownList. In the DropDownList, we defined onChange="ConfirmIt()" that will execute the JavaScript and will set value of Hidden Input Control to 1 if user selects the OK button and will set value to 0 when user selects Cancel button on the Confirm Dialog().

 Screen for Demostration

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<html><head runat="server"><title></title><script type="text/javascript">function ConfirmIt() {var x = confirm("Do you Want to notify changes to User ??");var control = '<%=inpHide.ClientID%>';if (x == true) {document.getElementById(control).value = "1";}else {document.getElementById(control).value = "0";}}</script></head><body><form id="form1" runat="server"><div><input id="inpHide" type="hidden" runat="server" /><asp:DropDownList ID="DropDownList1" runat="server"            onselectedindexchanged="DropDownList1_SelectedIndexChanged" onChange="ConfirmIt()"            AutoPostBack="True"><asp:ListItem>Item1</asp:ListItem><asp:ListItem>Item2</asp:ListItem><asp:ListItem>Item3</asp:ListItem></asp:DropDownList><asp:Label ID="Label1" runat="server" Text="Label"></asp:Label></div></form></body></html>

Now let's look at the code where we will retrieve the ConfirmDialog's return value at server-side.

Here is my code for the SelectedIndexChanged event of the DropDownList control. As you can see from this code, I simply use the Parse method and get the value of inpHide. If the value of this is 1, I know the OK button was pressed and if the value is 0, I know the Cancel button was pressed.

Code Behind

protected void DropDownList1_SelectedIndexChanged(object sender, EventArgs e)
    {int DiagResult = int.Parse(inpHide.Value);if (DiagResult == 1)
        {//Do SomthingResponse.Write("You Have Selected Ok");
        }else if (DiagResult == 0)
        {//Do somthingResponse.Write("You have Selected Cancel");

That's pretty simple and self explanatory code.i hope you like my article.

Sample Project Source

Download source files -2 kb

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He completed his Bachelor of Computer Application from Gujarat University 2009 .He is doing Master of Computer Application from Gujarat Technological University right now .. His area of Interests are Web Hacking , C# .net Windows form , , WPF ,Silverlight ,SQL Server and Some PHP.
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