Почему не работает пример кода date-fns с Vue?

import { format, formatDistance, formatRelative, subDays } from 'date-fns'
formatDistance(subDays(new Date(), 3), new Date())

import { formatDistance, subDays } from 'date-fns'

formattedValue () {
      return formatDistance(subDays(new Date(), 3), new Date())
    }