how to make an object point towards the mouse in unity

Vector3 difference = Camera.main.ScreenToWorldPoint(Input.mousePosition) - transform.position;
        difference.Normalize();
        float rotation_z = Mathf.Atan2(difference.y, difference.x) * Mathf.Rad2Deg;
        transform.rotation = Quaternion.Euler(0f, 0f, rotation_z + offset);

Vector3 mousePos = Input.mousePosition;
        mousePos = Camera.main.ScreenToWorldPoint(mousePos);
        Vector2 direction = new Vector2(mousePos.x - transform.position.x, mousePos.y - transform.position.y);
        transform.up = direction;

//Inside your update loop, add the following code:

//First, get the mouse position
Vector2 mousePosition = new Vector2 ( 
  Input.GetAxis("MouseX"), 
  Input.GetAxis("MouseY")
);
//Then, use unity's built-in lookAt function to do all the math for you:
transform.LookAt(mousePosition);

     using UnityEngine;     using System.Collections;          public class SCR_mouseRotation : MonoBehaviour {                  void Update () {             Vector3 mousePos = new Vector3(Input.mousePosition.x, Input.mousePosition.z, 10);             Vector3 lookPos = Camera.main.ScreenToWorldPoint(mousePos);             lookPos = lookPos - transform.position;             float angle = Mathf.Atan2(lookPos.z, lookPos.x) * Mathf.Rad2Deg;             transform.rotation = Quaternion.AngleAxis(angle, Vector3.down); // Turns Right                 transform.rotation = Quaternion.AngleAxis(angle, Vector3.up); //Turns Left                      }     }  

//Inside your update loop, add the following code:

//First, get the mouse position
Vector2 mousePosition = new Vector2 ( 
  Input.GetAxis("Mouse X"), 
  Input.GetAxis("Mouse Y"))
);
//Then, use unity's built-in lookAt function to do all the math for you:
transform.LookAt(mousePosition);