SelectionChanged プロパティ (DropDownClientEvents)

// The client event 'SelectionChanged' takes two parameters sender and e
// sender  is the object which is raising the event
// e is the DropDownSelectionEventArgs
function WebDropDown_SelectionChanged(sender, e) {

    //Gets the new collection of selected drop-down items
    //Only one item will be in the collection when multiple selection is disabled          
    var newSelection = e.getNewSelection();

    //Gets the text of the first drop-down item in the collection
    var text = newSelection[0].get_text();

    //Gets the index of the first drop-down item in the collection
    var index = newSelection[0].get_index();
           
    alert("Item '" + text + "' with index "+index+" is selected!");
    

}