WeakSet

//  `fn`  ,    .
function execRecursively(fn, subject, _refs = new WeakSet()) {
  //   
  if (_refs.has(subject)) {
    return;
  }

  fn(subject);
  if (typeof subject === "object" && subject) {
    _refs.add(subject);
    for (const key in subject) {
      execRecursively(fn, subject[key], _refs);
    }
    _refs.delete(subject);
  }
}

const foo = {
  foo: "Foo",
  bar: {
    bar: "Bar",
  },
};

foo.bar.baz = foo; //  !
execRecursively((obj) => console.log(obj), foo);

const ws = new WeakSet();
const foo = {};
const bar = {};

ws.add(foo);
ws.add(bar);

ws.has(foo); // true
ws.has(bar); // true

ws.delete(foo); //  foo  
ws.has(foo); // false, foo  
ws.has(bar); // true, bar