public class NewScript : MonoBehaviour {

public bool isStart = false;

if (isStart)
{
public GameObject obj;
}

}

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

[CreateAssetMenu(fileName = "New Item", menuName = "Item")]
public class Item : ScriptableObject {

    public new string name;
    public string description;
    public Sprite itemSprite;
    public int amount;
    
    public int healing;

    public ItemTypes itemTypes;
    public enum ItemTypes
    {
        Weapon, Food, Resources
    }

#if UNITY_EDITOR
    void OnValidate()
    {
        if (!Application.isPlaying)
        {
            if (itemTypes == ItemTypes.Weapon)
            {
                public int damage;
                public float fireRate;
                public float range;
            }
        }
    }
#endif

    void Start () {
  
    }    
}

itemTypes == ItemTypes.Weapon