feat(v2): lazy load algolia css so its not render blocking (#2125)

* perf(v2): algolia css should not be render blocking

* tweak

* lazy load css

* tweak

* tweak

* review

packages/docusaurus-theme-search-algolia/src/index.js

@@ -14,5 +14,25 @@ module.exports = function() {
     getThemePath() {
       return path.resolve(__dirname, './theme');
     },
+
+    configureWebpack() {
+      // Ensure that algolia docsearch css is its own chunk
+      return {
+        optimization: {
+          splitChunks: {
+            cacheGroups: {
+              algolia: {
+                name: 'algolia',
+                test: /algolia\.css$/,
+                chunks: `all`,
+                enforce: true,
+                // Set priority higher than docusaurus single-css extraction
+                priority: 60,
+              },
+            },
+          },
+        },
+      };
+    },
   };
 };

packages/docusaurus-theme-search-algolia/src/theme/SearchBar/index.js

@@ -11,10 +11,7 @@ import classnames from 'classnames';
 import useDocusaurusContext from '@docusaurus/useDocusaurusContext';
 import {useHistory} from '@docusaurus/router';
 
-import './styles.css';
-
-const loadJS = () => import('docsearch.js');
-let loadedJs = false;
+let loaded = false;
 
 const Search = props => {
   const initialized = useRef(false);
@@ -54,13 +51,15 @@ const Search = props => {
     }
   };
 
-  const loadAlgoliaJS = () => {
-    if (!loadedJs) {
-      loadJS().then(a => {
-        loadedJs = true;
-        window.docsearch = a.default;
-        initAlgolia();
-      });
+  const loadAlgolia = () => {
+    if (!loaded) {
+      Promise.all([import('docsearch.js'), import('./algolia.css')]).then(
+        ([{default: docsearch}]) => {
+          loaded = true;
+          window.docsearch = docsearch;
+          initAlgolia();
+        },
+      );
     } else {
       initAlgolia();
     }
@@ -99,8 +98,8 @@ const Search = props => {
           {'search-bar-expanded': props.isSearchBarExpanded},
           {'search-bar': !props.isSearchBarExpanded},
         )}
-        onClick={loadAlgoliaJS}
-        onMouseOver={loadAlgoliaJS}
+        onClick={loadAlgolia}
+        onMouseOver={loadAlgolia}
         onFocus={toggleSearchIconClick}
         onBlur={toggleSearchIconClick}
         ref={searchBarRef}

packages/docusaurus/src/webpack/base.ts

@@ -180,6 +180,7 @@ export function createBaseConfig(
     plugins: [
       new MiniCssExtractPlugin({
         filename: isProd ? '[name].[contenthash:8].css' : '[name].css',
+        chunkFilename: isProd ? '[name].[contenthash:8].css' : '[name].css',
         // remove css order warnings if css imports are not sorted alphabetically
         // see https://github.com/webpack-contrib/mini-css-extract-plugin/pull/422 for more reasoning
         ignoreOrder: true,