Object Rotation Limit! (JavaScript)

I already have this code for an object which is able to rotate on its y and z axis.

 var speed = 20;
 
 function Update () {
  
  if (Input.GetKey(KeyCode.A))
     transform.Rotate(Vector3.forward * speed * Time.deltaTime);
  
  if (Input.GetKey(KeyCode.D))
     transform.Rotate(-Vector3.forward * speed * Time.deltaTime);
  
   if (Input.GetKey(KeyCode.W))
     transform.Rotate(Vector3.up * speed * Time.deltaTime);
     
  if (Input.GetKey(KeyCode.S))
     transform.Rotate(-Vector3.up * speed * Time.deltaTime);
     
 }

Is it possible for me to limit the rotation of the object for each axis, so that the player cannot rotate more than 40 degrees in each angle?

Thanks in advance.