I'm positive that the solution to this is super simple, but I'm just not well-versed enough with Javascript to figure it out.

I'm trying to make a third-person shooter kind of thing, with the mouse controlling an empty game object ("aimer"), which the turret points towards to aim. This script is applied to the turret, and the empty game object is selected as the variable in the inspector.

 var aimer:GameObject;
 
 var zPos:float;
 
 function Start () {
     zPos = transform.position.z - Camera.main.transform.position.z;
 }
 
 function Update () {
     var xPos:float = aimer.x; //These lines are the problem. 
     var yPos:float = aimer.y; //I just don't know how to refer to "aimer."
     
     var cubeScreenPos:Vector3 = Camera.main.WorldToScreenPoint(transform.position);
     var newX:float = cubeScreenPos.x + (xPos - cubeScreenPos.x)/8;
     var newY:float = cubeScreenPos.y + (yPos - cubeScreenPos.y)/8;
     
 
     var vector3:Vector3 = Camera.main.ScreenToWorldPoint (Vector3(xPos, yPos, zPos));
     transform.position = vector3;
 }

There might be better ways of doing this whole thing, but I just really want to know how to fix this.

Thanks!