In this article I will explain how to call Code Behind (Server Side) methods or functions using Client Side JavaScript code in ASP.Net using C# and VB.Net.
The Code Behind (Server Side) function will be called using AJAX PageMethods and JavaScript.
Enabling PageMethods
The first thing you need to do is add a ASP.Net AJAX ScriptManager to the page and set its EnablePageMethods property to true as shown below
<asp:ScriptManager ID="ScriptManager1" runat="server" EnablePageMethods="true">
HTML Markup
<form id="form1" runat="server">
<asp:ScriptManager ID="ScriptManager1" runat="server" EnablePageMethods="true">
Your Name :
<asp:TextBox ID="txtUserName" runat="server" ></asp:TextBox>
<input id="btnGetTime" type="button" value="Show Current Time" onclick="ShowCurrentTime()"/>

As you noticed above I have added a textbox when user can enter his name and a HTML button that calls a JavaScript method to get the Current Time.
Client Side Methods
<script type="text/javascript">
function ShowCurrentTime() {
PageMethods.GetCurrentTime(document.getElementById("<%=txtUserName.ClientID%>").value, OnSuccess);
function OnSuccess(response, userContext, methodName) {

Above the ShowCurrentTime method makes an AJAX call to the server using ASP.Net AJAX ScriptManager PageMethods and executes the GetCurrentTime method which accepts the username and returns a string value.
Server Side Methods
public static string GetCurrentTime(string name)
return"Hello " + name + Environment.NewLine + "The Current Time is: "
        + DateTime.Now.ToString();

<System.Web.Services.WebMethod()> _
Public Shared Function GetCurrentTime(ByVal name AsString) AsString
Return"Hello "& name & Environment.NewLine &"The Current Time is: "& _

The above method simply returns a greeting message to the user along with the current server time. An important thing to note is that the method is declared as static (C#) and Shared(VB.Net) and also it is declared as Web Method unless you do this you won’t be able to call the methods using ASP.Net ScriptManager PageMethods.
The figure below displays the output displayed to the user when the button is clicked
Call Code Behind (Server Side) function from Client Side code in ASP.Net using C# and VB.Net