function Walk(obj)
{
    const set = new Set();
    function Step(obj, path="")
    {
        if(obj !== null && typeof obj === "object")
        {
            if(set.has(obj))
            {
                console.log("ive been to", obj, "quitting");
                return;
            }
            else
            {
                set.add(obj);
                console.log("ive never seen", obj, "here are its fields:");
                console.log("-----------------");
                for(let key in obj)
                {
                    const val = obj[key];
                    console.log("  >stepping into", path+"."+key);
                    Step(val, path+"."+key);
                }
                console.log("-----------------");
            }
        }
        else
        {
            console.log(obj, "is a leaf");
        }
    }
    Step(obj);
}


const root = {hey:"1", deep:{basement:{closet:{item1:"one", item2:"two"}}}, arr:["a", "b"]};
root.circ = root;
Walk(root);