What is the difference between a callback and a postback? A callback is a special postback, so a round-trip always occurs; however, unlike the classic postback, the script callback doesn't redraw the whole page. ViewState is not updated during a callback, it is for postback. How to make a callback? In the client side JavaScript code, if GetCallbackEventReference() method is reference, then when the JavaScript code is executed, a channel to the server is opened and an HTTP request is sent to the remote...