fix(algolia): fixed algolia indexing process

- Replaced .flatMap with es5 one-level-deep analog ported from blog
- added `matchField` options to algolia config, required after plugin upgrade

Author: Kirill Bolotsky

gatsby-config.js

@@ -206,6 +206,7 @@ if (
       appId: process.env.GATSBY_ALGOLIA_APP_ID,
       apiKey: process.env.ALGOLIA_ADMIN_KEY,
       enablePartialUpdates: true,
+      matchFields: ['title', 'slug', 'content'],
       queries,
       chunkSize: 10000, // default: 1000
     },

src/utils/algolia.js

@@ -9,6 +9,7 @@ const {
   dedupePath,
   removeGuidesAndRedirectWelcome,
   mdxAstToPlainText,
+  flat,
 } = require('./utils');
 
 const processMdxEntry = ({ children: [entry] }) => {
@@ -67,11 +68,10 @@ const flatten = (arr) => {
   while (pointer--) {
     cache[pointer] = processMdxEntry(arr[pointer]);
   }
-  return cache.flatMap((entry) => entry);
+  return flat(cache);
 };
 
 // main query
-// keep the length of excerpt really absurd to make sure the article comes in full
 const docPagesQuery = `{
   docPages: allFile(
     filter: { absolutePath: { regex: "/docs/" }, ext:{in: [".md"]} }

src/utils/utils.js

@@ -276,6 +276,11 @@ const mdxAstToPlainText = (ast) => {
   return $toString(ast);
 };
 
+// es5 tricky alternative to .flat
+// !warninng: support only 1 level deep
+// eslint-disable-next-line prefer-spread
+const flat = (arrays) => [].concat.apply([], arrays);
+
 /*
  * custom path processing rules, gatsby-node specific
  */
@@ -337,6 +342,9 @@ Object.defineProperties(utils, {
   getRandomKey: {
     value: getRandomKey,
   },
+  flat: {
+    value: flat,
+  },
   stripDirectoryPath: {
     value: stripDirectoryPath,
   },