Sanity Preview URL with sanityClient Fetch

resolveProductionUrl.js

import sanityClient from 'part:@sanity/base/client'

const remoteURL = 'https://example.com'
const localURL = 'http://localhost:8000'
const previewURL =
  window.location.hostname === 'localhost' ? localURL : remoteURL

export default function resolveProductionUrl (document) {
  if (!document.slug) return null

  if (document._type === 'page') {
    if (document.slug.current === 'home') {
      return `${previewURL}/`
    } else if (document.parentPage._ref) {
      const query = `*[page._id == '${document.parentPage._ref}']`
      sanityClient.fetch(query).then(parent => {
        parent.forEach(parentPage => {
          return `${parentPage.slug.current}/${previewURL}/`
        })
      })
    }
  } else if (document._type === 'post') {
    const categoryName = document.categories.length
      ? document.categories[0]._ref.replace('category-', '')
      : null

    if (!categoryName || categoryName !== 'blog') {
      return false
    }
    return `${previewURL}/${categoryName}/${document.slug.current}`
  } else if (document._type === 'office') {
    return `${previewURL}/office/${document.slug.current}`
  } else if (document._type === 'agent') {
    return `${previewURL}/agent/${document.slug.current}`
  }

  return `${previewURL}/${document.slug.current}`
}