var downkeys:Array=[];
stage.addEventListener(KeyboardEvent.KEY_DOWN,keyDown);
stage.addEventListener(KeyboardEvent.KEY_UP,keyUp);
stage.addEventListener(Event.ENTER_FRAME,tick);

function keyDown(e:KeyboardEvent):void{
    if(downkeys.indexOf(e.keyCode)<0){
        downkeys.push(e.keyCode);
    }
}
function keyUp(e:KeyboardEvent):void{
    var at:int=downkeys.indexOf(e.keyCode);
    if(at>-1){
        downkeys.splice(at,1);
    }
}
function tick(e:Event):void{
    if(downkeys.length>0){
        switch(downkeys[downkeys.length-1]){
            case 37: //left
                _x-=velocity;
                break;
            case 38: //up
                _y-=velocity;
                break;
            case 39: // right
                _x+=velocity;
                break;
            case 40: //down
                _y+=velocity;
                break;
        }
    }
}