Calling server side method through javascript Using Asp.net

this is a small example, it will call a server method without having the expense of postback

//step 1: Inherit ICallbackEventHandler interface in your form

public partial class FormCallServer: System.Web.UI.UserControl, ICallbackEventHandler
string m_callbackEventArgument = "";

//step 2:
protected void Page_Load(object sender, EventArgs e)
{

string callbackEventReference = Page.ClientScript.GetCallbackEventReference(this,
"document.getElementById('TextBox1').value ",
"ClientCallbackScript","null");

TextBox1.Attributes.Add("onChange", "javascript:" + callbackEventReference ); }

//step 3: Interface require to implement 2 monthods RaiseCallbackEvent and
//GetCallbackResult. These are predefined methods RaiseCallbackEvent initialise and
//GetCallbackResult will execute and return the output to called client method.

//below method is automatically called from client method
//notice parameter callbackEventArgument, it is an passed from client method, by this example it will be TextBox1.value (see which is mensioned above)

public void RaiseCallbackEvent(string callbackEventArgument)
{
m_callbackEventArgument = callbackEventArgument;
}

//below the main method for callback server method
public string GetCallbackResult()
{
//Your codes

return [you must return a string value]; //After executing this method it will below
//javascript function ClientCallbackScript
}

----------------------------------------------------------------------------
//step 4: you need some coding in client side also
//Argument result is the return value, after executing above GetCallbackResult

<Script type="text/javascript" >
function ClientCallbackScript(result)
{
//your code here
//a sample code from my side
document.getElementById('txtMyTestbox').value = result;
}

</Script >