We can pass parameters to Page methods and then the call back methods. We can pass the references to the four call back methods to call when the page method returns. The four call back methods are

·         onSucceed

·         onError

As we discussed we need to have callback function for success page method call and for unsuccessful page method call. Unsuccessful page method call means if there is an   internal server error on the page.

Using the call back method we can fetch the required result from the page and use it on the client script as required.

//CallBack method when the page call succeeds
function onSucceed(results, currentContext, methodName)
{
      alert(results);
}
 
//CallBack method when the page call fails due to interna, server error
function onError(results, currentContext, methodName)
{
      alert(results);
}

The method names and parameter names are user defined.  We can use any name for the callback methods and their parameters.

The OnSucceed parameter indicates the javascript function to be called when the call has succeeded and the result parameter has the result stored in it in our case the string returned from the code behind file.
The OnError parameter indicates the javascript function to be called when error occurs. The success call back method has three parameters:

·         Result – Returns the output of the page method.

·         currentContext – This is used to handle different logic when single callback is used for multiple page method requests. We can also pass array of values as userContext parameter.

·         methodName – This parameter returns the name of  page method called.

 The error call back method has three parameters:

·         Result – Returns the output of the page method.

·         currentContext – This is used to handle different logic when single callback is used for multiple page method requests. We can also pass array of values as userContext parameter.

·         methodName – This parameter returns the name of  page method called.

The result here return the type of the error, stacktrace, message and type of the exceptions. You can display the required information to the end user using the following   methods of error object

get_exceptionType()
get_mesage()
get_stackTrace()
get_statusCode()
get_timedOut()
 
function onError(result)
{
      alert(result.get_message());
}             

Sending the userContext parameter

var contextArray = "u1";     
PageMethods.GetStatus("p1","p2",onSucceed, onError,contextArray);  

And this can be used on the call back to execute different logic

function onSucceed(result,userContext,methodname)
{ 
      if (userContext = “u1”)
      {
            alert(result);
      }
}