const Chain = f => ({
  f,
  write: v => {
    f(() => console.log(v))
    return Chain(f)
  },
  wait: ms => Chain(next => setTimeout(() => f(next), ms))
})
let obj = Chain(next => next())

// test case:
// obj.write(4)
// obj.wait(1000)
// obj.write(4).write(3).write(2)
// obj.wait(1000).wait(2000).write(4)
// obj.wait(1000).write(1).wait(2000).write(2)
// obj.write(1).wait(1000).write(2)
// obj.wait(3000).write(1).write(2).wait(1000).write(3)