mutation.js

const val = {}
function setProp(obj, value) {
  obj.prop = value
  return obj
}

console.log(val, mutate(val, 'one'))

const obj1 = { val }
const obj2 = { val }

console.log(obj1, obj2, mutate(obj1.val, 'two'))

const ref = obj1.val

console.log(ref, obj1, obj2, mutate(ref, 'three'))