Clentside and server side programing in a button click

Question

Hi
I am using devexpress controls in my project. i want to do some client side and serverside code on button click event. My problem is after dispalying the alert , control is going to server side for further processing. I want to check textboexs entered or not. if not alert should come . I am clicking on the alert ok , its going to server code ,pls tell me the solution