ActionScript :: How To Make Code Run Under Certain Condition

package {
import flash.display.Sprite;
import flash.events.*;
import flash.net.FileReference;
import flash.net.FileReferenceList;
public class FileReferenceListExample extends Sprite {
[Code] .....

Code like the above will get executed as soon as loaded, how can I make it run under certain condition? Pretty much this in this answer:
function keyEvent(code:String):void {
// do something with the "code" parameter,
that looks like "alt+ctrl+D", may use .split('+'), etc
}