mongoose error

test.js

const mongoose = require('mongoose')

const Period = new mongoose.Schema({
  start: Date,
  end: Date
}, { _id: false })

const Cat = mongoose.model('Cat', {
  name: String,
  period: Period
})

async function test() {
  const db = await mongoose.connect('mongodb://localhost:27017/test', {useNewUrlParser: true})
  const period1 = {
    start: new Date('2018-01-01T10:00Z'),
    end: new Date('2018-01-01T15:00Z')
  }
  const kitty = new Cat({ name: 'Zildjian', period: period1 })
  console.log(kitty.toJSON())

  const period2 = {
    start: new Date('2018-01-02T15:00Z'),
    end: new Date('2018-01-02T20:00Z')
  }
  kitty.period = period2
  console.log(kitty.toJSON())

  await db.disconnect()
}

test()