We will use the same example used for the no error handling example.

Here is how we should make a callback with the data correctly:

        ob_post.AddParam("Number1", 49583);
        ob_post.AddParam("Number2", 83924);
        ob_post.post(null, 'onSum', clientFunction);
		

Next we will make the client side function with error handling, depending on the second argument of the function:

        function clientFunction(result, ex){
            if (ex != null){ // equivalent to if (result == null){
                switch (ex.type){
                    case 'InvalidCastException':
                        // the code to execute when one of the arguments is not of the correct type
                        alert ('One of the arguments is not of the correct type.');
                    break;
                    case 'ServerMethodNotImplemented':
                        // the server-side method name is not implemented
                        alert ('The server-side method was not found.');
                    break;
                    case 'MyException':
                        // an error is thrown by the user at server-side
                        alert ('I threw this exception server-side');
                    break;
                    case 'CallbackError':
                        // there was an error server side
                        alert ('There was an error server-side.');
                    break;
                }
            }
            else{
                alert("The sum is: " + result);
            }
        }
		

We will use ShowErrorsAtClient=false and ThrowExceptionsAtClient=true so we can show our own alert messages.

Click to test the correct callback:



If the ServerFileName is misspelled:



If the server method is misspelled:



If one of the arguments is not an integer:



If the numbers are equal:

Download this working example.

You may also check the debug for synchronous callback example to see the differences.