ASPNet Get Return Value from JavaScript function in Code Behind using C and VBNet

In this article I will explain with an example, how to get return value from JavaScript function in Code Behind of ASP.Net web application using C# and VB.Net.

The value will be returned from JavaScript function to Code Behind of ASP.Net web application using Hidden Field element in C# and VB.Net.

HTML Markup

Below is the HTML Markup of the sample that I have built. Here I have a button btnConfirm which will trigger the JavaScript Confirm method on its OnClientClick event. Then in the JavaScript Confirm method I store the input provided by the user in a dynamically created hidden field i.e. If OK is pressed I store value Yes and if Cancel is pressed I store No, so that we can pass the user inputs onto server side code. Then I allow the button to do normal PostBack and raise the OnClick event.

<head>

function Confirm() {

var confirm_value = document.createElement("INPUT");

confirm_value.type = "hidden";

confirm_value.name = "confirm_value";

if (confirm("Do you want to save data?")) {

confirm_value.value = "Yes";

} else {

confirm_value.value = "No";

}

document.forms[0].appendChild(confirm_value);

}

</script>

</head>

<body>

<asp:Button ID="btnConfirm" runat="server" OnClick="OnConfirm" Text="Raise Confirm" OnClientClick="Confirm()"/>

</form>

</body>

</html>

Fetching the User input server side

Now server side we need to fetch the user input that we stored in the dynamic hidden field and then based on whether user has selected OK or Cancel we need to execute different code. In order to simulate this process I have added alert box with different messages.

public void OnConfirm(object sender, EventArgs e)

{

string confirmValue = Request.Form["confirm_value"];

if (confirmValue == "Yes")

{

this.Page.ClientScript.RegisterStartupScript(this.GetType(), "alert", "alert('You clicked YES!')", true);

}

else

{

this.Page.ClientScript.RegisterStartupScript(this.GetType(), "alert", "alert('You clicked NO!')", true);

}

VB.Net