Gravity on a cube planet

Lets say that you are using rigidbodies for physics. You could add the following script to any object that would be affected by physics;

 //Following is C#, I can covert it to JS if you wish
 using UnityEngine;
 using System.Collections;
 
 public class Gravity : MonoBehaviour 
 {
 
     public Transform centreOfGravity;    //The object to gravitate towards, in this case the cube
     public float gravity = 1f;    //The force of the gravity to be applied
     public float maxDistance;    //The maximum distance from the centreOfGravity this object can be whilst still being affected by gravity
     
     private Rigidbody rb;
 
     // Use FixedUpdate for physics calculations
     void FixedUpdate () 
     {
         if (!GetComponent<Rigidbody>())
             return;    //If no rigidbody attached, return
         if (Vector3.Distance (transform.position, centreOfGravity.position) > maxDistance)
             return;    //If we are further than the max distance, return
 
         if (!rb)
             rb = GetComponent.<Rigidbody>();    //If the rb variable is null, get the rigidbody attached to this object
         if (rb.useGravity)
             rb.useGravity = false;    //Make sure the rigidbody isn't using the global gravity variable
         
         Vector3 direction = (centreOfGravity.position - transform.position).normalized;    //Get the direction of the cube and normalize so it doesn't have distance
         RaycastHit hit;    //Will contain information about the raycast we are about to perform
         if (centreOfGravity.GetComponent<Collider>().Raycast (transform.position, direction, hit, maxDistance))
             rb.AddForce (-hit.normal * gravity * rb.mass);    //Apply the force to the rigidbody towards the relative surface of the cube. *note* that this will multiply the force by the rigidbody's mass so that all objects will fall at the same rate. If you don't want this, remove that section
     }
 }