User side control means --controls never post the page to server. But it is possible to post a page server using user side control by javascript submit method. Where as server side control always submit the page to server. You can protect server side control post back by using javascript. Let you have to submit a page to server after client side validation then write javascript method and call the method by onclientclick event of server side control. In javascript method first check data validity then return true if data is valid otherwise return false which protect the server side control to postback the page.

User side control means --controls never post the page to server. But it is possible to post a page server using user side control by javascript submit method. Where as server side control always submit the page to server. You can protect server side control post back by using javascript. Let you have to submit a page to server after client side validation then write javascript method and call the method by onclientclick event of server side control. In javascript method first check data validity then return true if data is valid otherwise return false which protect the server side control to postback the page.