The baby periodically gets hungry or sleepy. The babysitter needs to be notified whenever the baby's state changes so he/she can help the baby. Add functionality to notify the babysitter. Please also support replacing a babysitter.

Baby.js

const States = {
  Default: 0,
  Hungry: 1,
  Sleepy: 2
}

class Baby {
  currentState = States.Default
  feedInterval = 0
  sleepInterval = 0

  start() {
    this.feedInterval = setInterval(
      () => this.updateState(States.Hungry), 2000)
    this.sleepInterval = setInterval(
      () => this.updateState(States.Sleepy), 5000)
  }

  stop() {
    clearInterval(this.feedInterval)
    clearInterval(this.sleepInterval)
  }

  updateState(state) {
    this.currentState = state
    console.log("The baby's state is ", state)
  }

  feed() {
    if (this.currentState != States.Hungry) {
      throw 'Not hungry'
    }

    this.currentState = States.Default
  }

  putToSleep() {
    if (this.currentState != States.Sleepy) {
      throw 'Not sleepy'
    }

    this.currentState = States.Default
  }
}

class Babysitter {

}

const baby = new Baby()
const babySitter = new Babysitter()
baby.start()