STEP BY STEP CLIENT SIDE GETTING SELECTED VALUE OF DROPDOWNLIST. Now the onchange-Event fires a client-side Javascript Event. It's free to sign up and bid on jobs. In the attached HTML code, The onchange event is working only for the pair. boolean: checked/unchecked (for checkboxes, radio and btn2state controls only) select: The onchange event is fired when the selection has changed. Click or control-click to add and remove toppings in the select list on the right and these choices will also be reflected in the total.