Indexing in Algolia using serverless functions (and observables!) https://www.sanity.io/blog/indexing-in-algolia-using-serverless-functions-and-observables

run.js

const algoliasearch = require('algoliasearch');
const request = require('request');

const ndjson = require('ndjson');
const {bindNodeCallback} = require('rxjs');
const {streamToRx} = require('rxjs-stream');
const {bufferCount, map, mergeMap, toArray, tap} = require('rxjs/operators');

// Algolia configuration
const algoliaApp = 'your_app_id';
const algoliaIndex = 'what_you_want_to_call_your_index';
// Sanity configuration
const projectId = 'your_project_id';
const dataset = 'your_dataset_name';
const sanityExportURL = `https://${projectId}.api.sanity.io/v1/data/export/${dataset}`;

module.exports = function indexContent(context, cb) {
  // Initiate an Algolia client
  const client = algoliasearch(algoliaApp, context.secrets.ALGOLIA_TOKEN);
  // Initiate the Algolia index
  const index = client.initIndex(algoliaIndex);

  // bind the update function to use it as an observable
  const partialUpdateObjects = bindNodeCallback((...args) => index.saveObjects(...args));
  streamToRx(
    request(sanityExportURL).pipe(ndjson())
  ).pipe(
    /* 
     * Pick and prepare fields you want to index,
     * here we reduce structured text to plain text
     */
    map(function sanityToAlgolia(doc) {
      return {
        objectID: doc._id,
        body: blocksToText(doc.body || []),
        blurb: blocksToText(doc.blurb || []),
        title: doc.title,
        name: doc.name,
        slug: doc.slug
      };
    }),
    // buffer batches in chunks of 100
    bufferCount(100),
    // 👇uncomment to console.log objects for debugging
    // tap(console.log),
    // submit actions, one batch at a time
    mergeMap(docs => partialUpdateObjects(docs), 1),
    // collect all batches and emit when the stream is complete
    toArray()
  )
    .subscribe(batchResults => {
      const totalLength = batchResults.reduce((count, batchResult) => count + batchResult.objectIDs.length, 0);
      cb(null, `Updated ${totalLength} documents in ${batchResults.length} batches`);
    }, cb);
};