How do i add a countdown timer in as3 that starts when the program begins?

Question

I also want it to remove everything that is on the stage when it reaches 0 and produce a Game Over screen.

Answer 1

import flash.events.TimerEvent;
import flash.utils.Timer;
var countdown:Timer = new Timer (1000,TARGET_TIME);
//after 60 Seconds every DisplayObject will be removed from stage
const TARGET_TIME:int = 60;
countdown.addEventListener(TimerEvent.TIMER, tick);
countdown.addEventListener(TimerEvent.TIMER_COMPLETE, gameOver);
function tick(e:TimerEvent):void {
    //this will count upwards 1.2.3.4....
    trace(e.currentTarget.currentCount);
function gameOver(e:TimerEvent):void {
    // this function will remove all DisplayObjects from your Stage
    // starting from the top
    //It will not remove shapes or anything the user might have drawn on the stage
    //just things that are accessible to ActionScript (Sprites, MovieClips)
    for (var i:int = this.numChildren-1 ; i >= 0; i--) {
        removeChildAt(i);
//countdown will start only if you call it explicitly
countdown.start();