Example of a custom Hook

useShipping.ts

const useShipping = (sellers: Seller[] = [], skuId: string) => {
  const [loading, setLoading] = useState(false)
  const [error, setError] = useState<string>(null)
  const [estimates, setEstimates] = useState<Sla[]>([])
  const { culture } = useRuntime()
  const client = useApolloClient()

  const getEstimates = (postalCode: string) => {
    setLoading(true)
    setError(null)
    client
      .query({
        query: getShippingEstimates,
        variables: {
          country: culture.country,
          postalCode,
          items: sellers.map(({ sellerId: seller }) => ({
            quantity: '1',
            id: skuId,
            seller,
          })),
        },
      })
      .then(({ data: { shipping: shippingData } }) => {
        const shipping = shippingData as Shipping
        const infos = shipping.logisticsInfo
        const slas = pluck('slas', infos)
        setEstimates(flatten(slas))
      })
      .catch(error => {
        setError(error.msg)
      })
      .finally(() => {
        setLoading(false)
      })
  }

  return { loading, estimates, getEstimates, error }
}