[AS3] Create shooting bullet AS2 to AS3

[Broth3R]

This code work fine in AS2, but how do you change it to AS3? I want to see the different between AS2 and AS3 and try to learn more about AS3.

//======= fireBullet creates a bullet and attaches a moveBullet behaviour to its onEnterFrame event
//
function fireBullet() {
	numBombs = getNextHighestDepth();
	attachMovie("bomb", "aBomb" + numBombs, numBombs);
	this["aBomb" + numBombs].onEnterFrame = moveBullet;
	with (this["aBomb" + numBombs]) {
		_xscale = _yscale = 75;
		_x = theTank._x;
		_y = theTank._y - theTank._height / 2;
	}
}
//
// ====== Basically moves each bullet up the screen; when it hits the top edge, or the bottom of the info_txt box, 
// we create and attach an explosion symbol at the point of contact, then remove the associated Bullet movie clip.
//
function moveBullet() {
	this._y -= 10;
	hit = this.hitTest(alien_mc);
	if (this._y < 0 || this.hitTest(_root["info_txt"]) || hit) {
		numExplosions = getNextHighestDepth();
		_root.attachMovie("explosion_mc", "explosion" + numExplosions, numExplosions);
		// ==== swapDepths just swaps the depths of two movieclips. Since we created info_txt first, it is "beneath" all of the other clips we've created.
		// swapping the depths "brings it the the front".  Try commenting out the line below to see why we need to swap. Can you explain what happens?
		//=================================
		_root["explosion" + numExplosions].swapDepths(_root["info_txt"]);
		_root["explosion" + numExplosions].onEnterFrame = function() {
			// response to the EnterFrame event for the explosion movie clip: don't want to loop exploding so get rid of ourselves after a single play;
			// uses the _currentframe & _totalframes properties to see if we've got to the end of the mc.
			if (this._currentframe > this._totalframes - 1) {
				removeMovieClip(this);
			}
		};
		with (_root["explosion" + numExplosions]) {
			_x = this._x;
			_y = this._y + 10;
			_xscale = _yscale = 50;
		}
		removeMovieClip(this);
		if (hit) {
			with (alien_mc) {
				_x = Math.random() * 500 + 20;
				_y = 0;
			}
		}
	}
}

[Broth3R]

This is just like the 'space invader' game