Top Down 2D Mouse Look

So, I am making a top down game, and instead of having my code make the player look to where ever the mouse cursor is, I want it to find where the mouse cursor is on start and then only move in response to what direction the mouse moves. Here is the code that I used, please respond in JS.

 var mouse_pos : Vector3;
 var target : Transform; //Assign to the object you want to rotate
 var object_pos : Vector3;
 var angle : float;
  
 function Update ()
 {
     mouse_pos = Input.mousePosition;
     mouse_pos.z = 5.23; //The distance between the camera and object
     object_pos = Camera.main.WorldToScreenPoint(target.position);
     mouse_pos.x = mouse_pos.x - object_pos.x;
     mouse_pos.y = mouse_pos.y - object_pos.y;
     angle = Mathf.Atan2(mouse_pos.y, mouse_pos.x) * Mathf.Rad2Deg;
     transform.rotation = Quaternion.Euler(Vector3(0, 0, angle));
 }