Difference betweening pushing button in actionscript 2 (as2) and as3, and more

To push a button in Actionscript 2 (As2), example:
 on (release) {
    play();
}

To push a button in Actionscript 3 (As3), example:
stop();
start_button1.addEventListener(MouseEvent.CLICK, clickFunction);
function clickFunction(event:MouseEvent):void {
gotoAndPlay(2);
}

Other difference between aAS2 and AS3:
AS2
btn_play._visible = false;
AS3
btn_play.visible = false;
vol_slider.visible = false;

AS2
    target = _parent;

AS3
    target = this.parent;

AS2

do_pause = function():Void{

AS3
var do_pause:Function = function():void{

AS2

if(mc._currentframe != mc._totalframes){

AS3

   if(mc.currentFrame != mc.totalFrames){