"use strict";

const obj = {
  a: {
    b: {
      c: {
        d: 2,
      },
    },
  },
};

const a = obj?.a;
expect(a).toBe(obj.a);

const b = obj?.a?.b;
expect(b).toBe(obj.a.b);

const bad = obj?.b?.b;
expect(bad).toBeUndefined();

let val;
val = obj?.a?.b;
expect(val).toBe(obj.a.b);

expect(() => {
  const bad = obj?.b.b;
}).toThrow();