``` const idx = (p, o) => p.reduce((a, b) => o && o[b] ? o[b] : null, o); const props = { user: { posts: [{ title: "Foo", comments: ['good one', '有趣'], }, { title: "Bar", comments: ['Ok'], }, { title: "Baz", comments: [], }] } }; console.log(idx(['user', 'posts', '0', 'comments'])); // ['good one','有趣'] ```