{
  "one object at four places": (() => {
    const shared = { v: 1 };
    return { a: shared, b: shared, c: [shared, { d: shared }] };
  })(),
}

--

one object at four places:
{a:{v:1},b:{v:1},c:[{v:1},{d:{v:1}}]}
{
  a: {
    v: 1
  },
  b: {
    v: 1
  },
  c: [
    {
      v: 1
    },
    {
      d: {
        v: 1
      }
    }
  ]
}
{
  a: {
    v: 1
  },
  b: {
    v: 1
  },
  c: [
    {
      v: 1
    },
    {
      d: {
        v: 1
      }
    }
  ]
}