generateAssetsList.js

const generateAssetsList = (posts, baseUrl, simpleLog = console.log) => new Promise(async resolve =>{
  const apiURL = `${baseUrl.replace(/\/$/, '')}/wp-json/wp/v2/media`
  simpleLog('Reducing posts to asset numbers')
  let infosFetched = 0
  
  // First add the featured_media images and get ther URLs.
  const featuredAssets = await Promise.all(posts.reduce((all, post) => {
    if (!post.featured_media) return all
    return all.concat([{
      mediaNumber: post.featured_media,
      postId: post.id
    }])
  }, [])
  .map(async ({mediaNumber, postId}, i , array) => {
    const featuredMedia = await getJSON(`${apiURL}/${mediaNumber}`)
    infosFetched += 1
    simpleLog(`Getting info about assets ${infosFetched}/${array.length}`)
    return {
      mediaNumber,
      link: featuredMedia.guid.rendered,
      title: featuredMedia.title.rendered || `asset${i}`,
      description: featuredMedia.alt_text || '',
      postId 
    }
    // After all this we also add images from the body of posts.
  }))
  const assets = featuredAssets.concat(posts.reduce((all, post) => {
    const images = post.bodyImages ? post.bodyImages : []
    return all.concat(images)
  }, []))

  resolve(assets)
  
})