hotel.js

function substractIdArrays(a, b) {
  return a.filter(x => !b.find(y => y + '' === x + ''))
}

async function updateArea(areaCode) {
  const area = await Area.findOne({ areaCode })

  const associatedHotels = await Hotel.find({ areaCode }).then(hotels => hotels.map(h => h._id))

  const hotelsInArea = await Hotel.find({
    location: {
      $geoWithin: {
        $geometry: area.polygon
      }
    }
  }).then(hotels => hotels.map(h => h._id))

  const hotelsToAdd = substractIdArrays(hotelsInArea, associatedHotels)
  const hotelsToRemove = substractIdArrays(associatedHotels, hotelsInArea)
}