Help from AS2 to AS3

Hi everyone

As a beginner I having a lot of difficulties upgrade my website fom AS2 to AS3.
I use to use a amazing piece of code that I found in this website in order to scroll the background using the mouse. It was perfect but have to upgrade…

stop();
this.onMouseMove = function() {
	constrainedMove(BigMC_mc, 30, -1);
};
function constrainedMove(target:MovieClip, speed:Number, dir:Number) {
	var mSpeed:Number;
	var mousePercentX:Number = _xmouse/Stage.width;
	
	if (dir == 1) {
		mSpeed = 1-mousePercent;
		
	} else {
		mSpeed = mousePercent;
		
	}
	target.destY = Math.round(-((target._height-Stage.height)*mSpeed));
	
	target.onEnterFrame = function() {
		if (target._y == target.destY) {
			delete target.onEnterFrame;
		} else if (target._y>target.destY) {
			target._y -= Math.ceil((target._y-target.destY)*(speed/100));
		} else if (target._y<target.destY) {
			target._y += Math.ceil((target.destY-target._y)*(speed/100));
		}
				if ((target._y+target._height)<Stage.height) {
			target._y=Stage.height-target._height
		}
		if ((target._y)>0) {
			target._y=0
		}
ç

I really don’t get AS3 and wonder if anyone here has already translated this code. If yes It would be very helpful for me. If not, where can I find a code which has the same function or similar but in AS3 ?

Thanx a lot !