diff --git a/.eslintrc.js b/.eslintrc.js
index 7dcdc4bc55c2..28cfb8e15acb 100644
--- a/.eslintrc.js
+++ b/.eslintrc.js
@@ -88,16 +88,11 @@ module.exports = {
 
     // TODO re-enable some these as errors
     // context: https://github.com/facebook/docusaurus/pull/2949
-    '@typescript-eslint/no-var-requires': WARNING,
     '@typescript-eslint/ban-ts-comment': WARNING,
     '@typescript-eslint/ban-types': WARNING,
-    'import/no-duplicates': WARNING,
     'import/prefer-default-export': WARNING,
     'import/no-extraneous-dependencies': WARNING,
-    'prefer-const': WARNING,
     'no-useless-escape': WARNING,
-    'prefer-object-spread': WARNING,
-    'no-return-await': WARNING,
     'prefer-template': WARNING,
     'no-shadow': WARNING,
     'no-param-reassign': WARNING,
@@ -113,7 +108,6 @@ module.exports = {
     'no-useless-return': WARNING,
     '@typescript-eslint/no-empty-function': WARNING,
     'global-require': WARNING,
-    'import/newline-after-import': WARNING,
     'prefer-destructuring': WARNING,
     yoda: WARNING,
     'no-control-regex': WARNING,
@@ -133,5 +127,13 @@ module.exports = {
         'header/header': OFF,
       },
     },
+    {
+      files: ['*.js'],
+      rules: {
+        // Make JS code directly runnable in Node.
+        '@typescript-eslint/no-var-requires': OFF,
+        '@typescript-eslint/explicit-module-boundary-types': OFF,
+      },
+    },
   ],
 };
diff --git a/packages/docusaurus-plugin-client-redirects/src/__tests__/collectRedirects.test.ts b/packages/docusaurus-plugin-client-redirects/src/__tests__/collectRedirects.test.ts
index ebcdffab00a0..446c2d65d871 100644
--- a/packages/docusaurus-plugin-client-redirects/src/__tests__/collectRedirects.test.ts
+++ b/packages/docusaurus-plugin-client-redirects/src/__tests__/collectRedirects.test.ts
@@ -17,7 +17,7 @@ function createTestPluginContext(
   return {
     outDir: '/tmp',
     baseUrl: 'https://docusaurus.io',
-    routesPaths: routesPaths,
+    routesPaths,
     options: normalizePluginOptions(options),
   };
 }
@@ -192,7 +192,7 @@ describe('collectRedirects', () => {
                   `/def?queryString=toto`,
                 ];
               }
-              return;
+              return undefined;
             },
           },
           ['/'],
@@ -210,7 +210,7 @@ describe('collectRedirects', () => {
               if (routePath === '/') {
                 return [[`/fromPath`]] as any;
               }
-              return;
+              return undefined;
             },
           },
           ['/'],
diff --git a/packages/docusaurus-plugin-client-redirects/src/__tests__/redirectValidation.test.ts b/packages/docusaurus-plugin-client-redirects/src/__tests__/redirectValidation.test.ts
index da2b80db5733..981b5680f6c0 100644
--- a/packages/docusaurus-plugin-client-redirects/src/__tests__/redirectValidation.test.ts
+++ b/packages/docusaurus-plugin-client-redirects/src/__tests__/redirectValidation.test.ts
@@ -51,14 +51,14 @@ describe('validateRedirect', () => {
 
     expect(() =>
       validateRedirect({
-        from: null as any,
+        from: (null as unknown) as string,
         to: '/toSomePath?queryString=xyz',
       }),
     ).toThrowErrorMatchingSnapshot();
 
     expect(() =>
       validateRedirect({
-        from: ['heyho'] as any,
+        from: (['heyho'] as unknown) as string,
         to: '/toSomePath?queryString=xyz',
       }),
     ).toThrowErrorMatchingSnapshot();
diff --git a/packages/docusaurus-plugin-client-redirects/src/__tests__/writeRedirectFiles.test.ts b/packages/docusaurus-plugin-client-redirects/src/__tests__/writeRedirectFiles.test.ts
index d24c3b5aa890..0a907ef6f2ad 100644
--- a/packages/docusaurus-plugin-client-redirects/src/__tests__/writeRedirectFiles.test.ts
+++ b/packages/docusaurus-plugin-client-redirects/src/__tests__/writeRedirectFiles.test.ts
@@ -69,7 +69,7 @@ describe('toRedirectFilesMetadata', () => {
 
 describe('writeRedirectFiles', () => {
   test('write the files', async () => {
-    const outDir = '/tmp/docusaurus_tests_' + Math.random();
+    const outDir = `/tmp/docusaurus_tests_${Math.random()}`;
 
     const filesMetadata = [
       {
@@ -94,7 +94,7 @@ describe('writeRedirectFiles', () => {
   });
 
   test('avoid overwriting existing files', async () => {
-    const outDir = '/tmp/docusaurus_tests_' + Math.random();
+    const outDir = `/tmp/docusaurus_tests_${Math.random()}`;
 
     const filesMetadata = [
       {
diff --git a/packages/docusaurus-plugin-client-redirects/src/extensionRedirects.ts b/packages/docusaurus-plugin-client-redirects/src/extensionRedirects.ts
index df4a7110f2e0..9adebf43b437 100644
--- a/packages/docusaurus-plugin-client-redirects/src/extensionRedirects.ts
+++ b/packages/docusaurus-plugin-client-redirects/src/extensionRedirects.ts
@@ -53,7 +53,7 @@ export function createToExtensionsRedirects(
     if (extensionFound) {
       const routePathWithoutExtension = removeSuffix(path, extensionFound);
       return [routePathWithoutExtension].map((from) => ({
-        from: from,
+        from,
         to: path,
       }));
     }
@@ -78,12 +78,11 @@ export function createFromExtensionsRedirects(
   const createPathRedirects = (path: string): RedirectMetadata[] => {
     if (path === '' || path.endsWith('/') || alreadyEndsWithAnExtension(path)) {
       return [];
-    } else {
-      return extensions.map((ext) => ({
-        from: `${path}.${ext}`,
-        to: path,
-      }));
     }
+    return extensions.map((ext) => ({
+      from: `${path}.${ext}`,
+      to: path,
+    }));
   };
 
   return flatten(paths.map(createPathRedirects));
diff --git a/packages/docusaurus-plugin-client-redirects/src/normalizePluginOptions.ts b/packages/docusaurus-plugin-client-redirects/src/normalizePluginOptions.ts
index 3a9e9342c0cf..206de9f07d79 100644
--- a/packages/docusaurus-plugin-client-redirects/src/normalizePluginOptions.ts
+++ b/packages/docusaurus-plugin-client-redirects/src/normalizePluginOptions.ts
@@ -21,7 +21,7 @@ export const DefaultPluginOptions: PluginOptions = {
 };
 
 function isRedirectsCreator(
-  value: any,
+  value: unknown,
 ): value is CreateRedirectsFnOption | undefined {
   if (value === null || typeof value === 'undefined') {
     return true;
diff --git a/packages/docusaurus-plugin-client-redirects/src/redirectValidation.ts b/packages/docusaurus-plugin-client-redirects/src/redirectValidation.ts
index c300ff2d6ae0..184e41cc22f3 100644
--- a/packages/docusaurus-plugin-client-redirects/src/redirectValidation.ts
+++ b/packages/docusaurus-plugin-client-redirects/src/redirectValidation.ts
@@ -21,7 +21,7 @@ const RedirectSchema = Yup.object<RedirectMetadata>({
   to: PathnameValidator.required(),
 });
 
-export function validateRedirect(redirect: RedirectMetadata) {
+export function validateRedirect(redirect: RedirectMetadata): void {
   try {
     RedirectSchema.validateSync(redirect, {
       strict: true,
diff --git a/packages/docusaurus-plugin-client-redirects/src/writeRedirectFiles.ts b/packages/docusaurus-plugin-client-redirects/src/writeRedirectFiles.ts
index d8b41a3de964..dbd3d6bbdff0 100644
--- a/packages/docusaurus-plugin-client-redirects/src/writeRedirectFiles.ts
+++ b/packages/docusaurus-plugin-client-redirects/src/writeRedirectFiles.ts
@@ -54,7 +54,9 @@ export function toRedirectFilesMetadata(
   return redirects.map(createFileMetadata);
 }
 
-export async function writeRedirectFile(file: RedirectFileMetadata) {
+export async function writeRedirectFile(
+  file: RedirectFileMetadata,
+): Promise<void> {
   try {
     // User-friendly security to prevent file overrides
     if (await fs.pathExists(file.fileAbsolutePath)) {
@@ -79,6 +81,6 @@ export async function writeRedirectFile(file: RedirectFileMetadata) {
 
 export default async function writeRedirectFiles(
   redirectFiles: RedirectFileMetadata[],
-) {
+): Promise<void> {
   await Promise.all(redirectFiles.map(writeRedirectFile));
 }
diff --git a/packages/docusaurus-plugin-content-blog/package.json b/packages/docusaurus-plugin-content-blog/package.json
index 46f72ee841f7..438be5766bfc 100644
--- a/packages/docusaurus-plugin-content-blog/package.json
+++ b/packages/docusaurus-plugin-content-blog/package.json
@@ -11,11 +11,9 @@
     "access": "public"
   },
   "license": "MIT",
-  "devDependencies": {
-    "@docusaurus/types": "^2.0.0-alpha.58"
-  },
   "dependencies": {
     "@docusaurus/mdx-loader": "^2.0.0-alpha.58",
+    "@docusaurus/types": "^2.0.0-alpha.58",
     "@docusaurus/utils": "^2.0.0-alpha.58",
     "feed": "^4.1.0",
     "fs-extra": "^8.1.0",
diff --git a/packages/docusaurus-plugin-content-blog/src/blogUtils.ts b/packages/docusaurus-plugin-content-blog/src/blogUtils.ts
index b5b29c5266d4..b5bc9366f852 100644
--- a/packages/docusaurus-plugin-content-blog/src/blogUtils.ts
+++ b/packages/docusaurus-plugin-content-blog/src/blogUtils.ts
@@ -19,7 +19,7 @@ import {
 } from '@docusaurus/utils';
 import {LoadContext} from '@docusaurus/types';
 
-export function truncate(fileString: string, truncateMarker: RegExp) {
+export function truncate(fileString: string, truncateMarker: RegExp): string {
   return fileString.split(truncateMarker, 1).shift()!;
 }
 
@@ -37,7 +37,7 @@ function toUrl({date, link}: DateLink) {
 export async function generateBlogFeed(
   context: LoadContext,
   options: PluginOptions,
-) {
+): Promise<Feed | null> {
   if (!options.feedOptions) {
     throw new Error(
       'Invalid options - `feedOptions` is not expected to be null.',
@@ -76,7 +76,7 @@ export async function generateBlogFeed(
     } = post;
     feed.addItem({
       title,
-      id: id,
+      id,
       link: normalizeUrl([siteUrl, permalink]),
       date,
       description,
@@ -90,7 +90,7 @@ export async function generateBlogPosts(
   blogDir: string,
   {siteConfig, siteDir}: LoadContext,
   options: PluginOptions,
-) {
+): Promise<BlogPost[]> {
   const {
     include,
     routeBasePath,
@@ -181,14 +181,16 @@ export function linkify(
   siteDir: string,
   blogPath: string,
   blogPosts: BlogPost[],
-) {
+): string {
   let fencedBlock = false;
   const lines = fileContent.split('\n').map((line) => {
     if (line.trim().startsWith('```')) {
       fencedBlock = !fencedBlock;
     }
 
-    if (fencedBlock) return line;
+    if (fencedBlock) {
+      return line;
+    }
 
     let modifiedLine = line;
     const mdRegex = /(?:(?:\]\()|(?:\]:\s?))(?!https)([^'")\]\s>]+\.mdx?)/g;
diff --git a/packages/docusaurus-plugin-content-docs/package.json b/packages/docusaurus-plugin-content-docs/package.json
index 494ea0e15a6b..cdae0b87f962 100644
--- a/packages/docusaurus-plugin-content-docs/package.json
+++ b/packages/docusaurus-plugin-content-docs/package.json
@@ -12,12 +12,12 @@
   },
   "license": "MIT",
   "devDependencies": {
-    "@docusaurus/types": "^2.0.0-alpha.58",
     "commander": "^5.0.0",
     "picomatch": "^2.1.1"
   },
   "dependencies": {
     "@docusaurus/mdx-loader": "^2.0.0-alpha.58",
+    "@docusaurus/types": "^2.0.0-alpha.58",
     "@docusaurus/utils": "^2.0.0-alpha.58",
     "execa": "^3.4.0",
     "fs-extra": "^8.1.0",
diff --git a/packages/docusaurus-plugin-content-docs/src/__tests__/index.test.ts b/packages/docusaurus-plugin-content-docs/src/__tests__/index.test.ts
index 195cb8d12e99..7edfe16efef0 100644
--- a/packages/docusaurus-plugin-content-docs/src/__tests__/index.test.ts
+++ b/packages/docusaurus-plugin-content-docs/src/__tests__/index.test.ts
@@ -310,7 +310,7 @@ describe('versioned website', () => {
         permalink: '/docs/next/',
       },
     });
-    expect(docsMetadata['hello']).toEqual({
+    expect(docsMetadata.hello).toEqual({
       id: 'hello',
       isDocsHomePage: true,
       permalink: '/docs/next/',
diff --git a/packages/docusaurus-plugin-content-docs/src/index.ts b/packages/docusaurus-plugin-content-docs/src/index.ts
index 6740c9e40715..8b8a6c136e2a 100644
--- a/packages/docusaurus-plugin-content-docs/src/index.ts
+++ b/packages/docusaurus-plugin-content-docs/src/index.ts
@@ -68,7 +68,7 @@ const DEFAULT_OPTIONS: PluginOptions = {
 function getFirstDocLinkOfSidebar(
   sidebarItems: DocsSidebarItem[],
 ): string | null {
-  for (let sidebarItem of sidebarItems) {
+  for (const sidebarItem of sidebarItems) {
     if (sidebarItem.type === 'category') {
       const url = getFirstDocLinkOfSidebar(sidebarItem.items);
       if (url) {
@@ -534,7 +534,7 @@ Available document ids=
                   options: {
                     siteDir,
                     docsDir,
-                    sourceToPermalink: sourceToPermalink,
+                    sourceToPermalink,
                     versionedDir,
                   },
                 },
diff --git a/packages/docusaurus-plugin-content-docs/src/markdown/linkify.ts b/packages/docusaurus-plugin-content-docs/src/markdown/linkify.ts
index 16292b9122fa..66250aac26a8 100644
--- a/packages/docusaurus-plugin-content-docs/src/markdown/linkify.ts
+++ b/packages/docusaurus-plugin-content-docs/src/markdown/linkify.ts
@@ -17,7 +17,7 @@ export default function (
   siteDir: string,
   sourceToPermalink: SourceToPermalink,
   versionedDir?: string,
-) {
+): string {
   // Determine the source dir. e.g: /website/docs, /website/versioned_docs/version-1.0.0
   let sourceDir: string | undefined;
   const thisSource = filePath;
@@ -40,7 +40,9 @@ export default function (
       if (line.trim().startsWith('```')) {
         fencedBlock = !fencedBlock;
       }
-      if (fencedBlock) return line;
+      if (fencedBlock) {
+        return line;
+      }
 
       let modifiedLine = line;
       // Replace inline-style links or reference-style links e.g:
diff --git a/packages/docusaurus-plugin-content-docs/src/sidebars.ts b/packages/docusaurus-plugin-content-docs/src/sidebars.ts
index 6054eab42a95..6256e06c51a9 100644
--- a/packages/docusaurus-plugin-content-docs/src/sidebars.ts
+++ b/packages/docusaurus-plugin-content-docs/src/sidebars.ts
@@ -135,7 +135,7 @@ function normalizeItem(item: SidebarItemRaw): SidebarItem[] {
     case 'doc':
       assertIsDoc(item);
       return [item];
-    default:
+    default: {
       const extraMigrationError =
         item.type === 'subcategory'
           ? "Docusaurus v2: 'subcategory' has been renamed as 'category'"
@@ -145,6 +145,7 @@ function normalizeItem(item: SidebarItemRaw): SidebarItem[] {
           item.type
         }]. Sidebar item=${JSON.stringify(item)} ${extraMigrationError}`,
       );
+    }
   }
 }
 
@@ -168,7 +169,7 @@ function normalizeSidebar(sidebars: SidebarRaw): Sidebar {
 
 export default function loadSidebars(sidebarPaths?: string[]): Sidebar {
   // We don't want sidebars to be cached because of hot reloading.
-  let allSidebars: SidebarRaw = {};
+  const allSidebars: SidebarRaw = {};
 
   if (!sidebarPaths || !sidebarPaths.length) {
     return {} as Sidebar;
diff --git a/packages/docusaurus-plugin-content-docs/src/version.ts b/packages/docusaurus-plugin-content-docs/src/version.ts
index 9edee1c3285d..ba4350658e72 100644
--- a/packages/docusaurus-plugin-content-docs/src/version.ts
+++ b/packages/docusaurus-plugin-content-docs/src/version.ts
@@ -19,7 +19,7 @@ export function docsVersion(
   version: string | null | undefined,
   siteDir: string,
   options: PathOptions,
-) {
+): void {
   if (!version) {
     throw new Error(
       'No version tag specified!. Pass the version you wish to create as an argument. Ex: 1.0.0',
diff --git a/packages/docusaurus-plugin-sitemap/src/__tests__/createSitemap.test.ts b/packages/docusaurus-plugin-sitemap/src/__tests__/createSitemap.test.ts
index 8f75ac8fad7f..a1bebc09f694 100644
--- a/packages/docusaurus-plugin-sitemap/src/__tests__/createSitemap.test.ts
+++ b/packages/docusaurus-plugin-sitemap/src/__tests__/createSitemap.test.ts
@@ -28,7 +28,7 @@ describe('createSitemap', () => {
 
   test('empty site', () => {
     expect(() => {
-      createSitemap({} as any, [], {} as any);
+      createSitemap({} as DocusaurusConfig, [], {} as any);
     }).toThrowErrorMatchingInlineSnapshot(
       `"url in docusaurus.config.js cannot be empty/undefined"`,
     );
diff --git a/packages/docusaurus-plugin-sitemap/src/index.ts b/packages/docusaurus-plugin-sitemap/src/index.ts
index b7a5acf75f5a..6be26f554d2a 100644
--- a/packages/docusaurus-plugin-sitemap/src/index.ts
+++ b/packages/docusaurus-plugin-sitemap/src/index.ts
@@ -9,7 +9,7 @@ import fs from 'fs-extra';
 import path from 'path';
 import {PluginOptions} from './types';
 import createSitemap from './createSitemap';
-import {LoadContext, Props} from '@docusaurus/types';
+import {LoadContext, Props, Plugin} from '@docusaurus/types';
 
 const DEFAULT_OPTIONS: PluginOptions = {
   cacheTime: 600 * 1000, // 600 sec - cache purge period.
@@ -20,7 +20,7 @@ const DEFAULT_OPTIONS: PluginOptions = {
 export default function pluginSitemap(
   _context: LoadContext,
   opts: Partial<PluginOptions>,
-) {
+): Plugin<void> {
   const options = {...DEFAULT_OPTIONS, ...opts};
 
   return {
diff --git a/packages/docusaurus-utils/src/index.ts b/packages/docusaurus-utils/src/index.ts
index 69076f3985e5..6929fd1bf888 100644
--- a/packages/docusaurus-utils/src/index.ts
+++ b/packages/docusaurus-utils/src/index.ts
@@ -197,7 +197,7 @@ export function createExcerpt(fileString: string): string | undefined {
 
   const fileLines = fileContent.split('\n');
 
-  for (let fileLine of fileLines) {
+  for (const fileLine of fileLines) {
     const cleanedLine = fileLine
       // Remove HTML tags.
       .replace(/<[^>]*>/g, '')
@@ -338,14 +338,17 @@ export function normalizeUrl(rawUrls: string[]): string {
  * don't expose user's site structure.
  * Example: some/path/to/website/docs/foo.md -> @site/docs/foo.md
  */
-export function aliasedSitePath(filePath: string, siteDir: string) {
+export function aliasedSitePath(filePath: string, siteDir: string): string {
   const relativePath = path.relative(siteDir, filePath);
   // Cannot use path.join() as it resolves '../' and removes
   // the '@site'. Let webpack loader resolve it.
   return `@site/${relativePath}`;
 }
 
-export function getEditUrl(fileRelativePath: string, editUrl?: string) {
+export function getEditUrl(
+  fileRelativePath: string,
+  editUrl?: string,
+): string | undefined {
   return editUrl
     ? normalizeUrl([editUrl, posixPath(fileRelativePath)])
     : undefined;
@@ -362,22 +365,22 @@ export function isValidPathname(str: string): boolean {
   }
 }
 
-export function addTrailingSlash(str: string) {
+export function addTrailingSlash(str: string): string {
   return str.endsWith('/') ? str : `${str}/`;
 }
 
-export function removeTrailingSlash(str: string) {
+export function removeTrailingSlash(str: string): string {
   return removeSuffix(str, '/');
 }
 
-export function removeSuffix(str: string, suffix: string) {
+export function removeSuffix(str: string, suffix: string): string {
   if (suffix === '') {
     return str; // always returns "" otherwise!
   }
   return str.endsWith(suffix) ? str.slice(0, -suffix.length) : str;
 }
 
-export function getFilePathForRoutePath(routePath: string) {
+export function getFilePathForRoutePath(routePath: string): string {
   const fileName = path.basename(routePath);
   const filePath = path.dirname(routePath);
   return path.join(filePath, `${fileName}/index.html`);
diff --git a/packages/docusaurus/package.json b/packages/docusaurus/package.json
index 08efb92b9aaa..7faf83f049eb 100644
--- a/packages/docusaurus/package.json
+++ b/packages/docusaurus/package.json
@@ -30,8 +30,7 @@
     "url": "https://github.com/facebook/docusaurus/issues"
   },
   "devDependencies": {
-    "@docusaurus/module-type-aliases": "^2.0.0-alpha.58",
-    "@docusaurus/types": "^2.0.0-alpha.58"
+    "@docusaurus/module-type-aliases": "^2.0.0-alpha.58"
   },
   "dependencies": {
     "@babel/core": "^7.9.0",
@@ -41,6 +40,7 @@
     "@babel/preset-react": "^7.9.4",
     "@babel/preset-typescript": "^7.9.0",
     "@babel/runtime": "^7.9.2",
+    "@docusaurus/types": "^2.0.0-alpha.58",
     "@docusaurus/utils": "^2.0.0-alpha.58",
     "@endiliey/static-site-generator-webpack-plugin": "^4.0.0",
     "@svgr/webpack": "^5.4.0",
diff --git a/packages/docusaurus/src/babel/preset.ts b/packages/docusaurus/src/babel/preset.ts
index e6fafd65a872..479244538155 100644
--- a/packages/docusaurus/src/babel/preset.ts
+++ b/packages/docusaurus/src/babel/preset.ts
@@ -50,6 +50,7 @@ function getTransformOptions(isServer: boolean): TransformOptions {
           // By default, it assumes @babel/runtime@7.0.0. Since we use >7.0.0, better to
           // explicitly specify the version so that it can reuse the helper better
           // See https://github.com/babel/babel/issues/10261
+          // eslint-disable-next-line @typescript-eslint/no-var-requires
           version: require('@babel/runtime/package.json').version,
           regenerator: true,
           useESModules: true,
@@ -74,8 +75,8 @@ function getTransformOptions(isServer: boolean): TransformOptions {
 }
 
 function babelPresets(api: ConfigAPI): TransformOptions {
-  const caller = api.caller((caller) => caller?.name);
-  return getTransformOptions(caller === 'server');
+  const callerName = api.caller((caller) => caller?.name);
+  return getTransformOptions(callerName === 'server');
 }
 
 export = babelPresets;
diff --git a/packages/docusaurus/src/client/App.tsx b/packages/docusaurus/src/client/App.tsx
index 40d4f4249154..4bb3aba05dd7 100644
--- a/packages/docusaurus/src/client/App.tsx
+++ b/packages/docusaurus/src/client/App.tsx
@@ -15,7 +15,7 @@ import PendingNavigation from './PendingNavigation';
 
 import './client-lifecycles-dispatcher';
 
-function App() {
+function App(): JSX.Element {
   const [isClient, setIsClient] = useState(false);
 
   useEffect(() => {
diff --git a/packages/docusaurus/src/client/docusaurus.ts b/packages/docusaurus/src/client/docusaurus.ts
index 2bbe88de3475..4bd19beb5bf6 100644
--- a/packages/docusaurus/src/client/docusaurus.ts
+++ b/packages/docusaurus/src/client/docusaurus.ts
@@ -15,6 +15,7 @@ const fetched = {};
 const loaded = {};
 
 declare global {
+  // eslint-disable-next-line camelcase
   const __webpack_require__: any;
   interface Navigator {
     connection: any;
diff --git a/packages/docusaurus/src/client/exports/Head.tsx b/packages/docusaurus/src/client/exports/Head.tsx
index 0955cb89abcd..f699f3606d72 100644
--- a/packages/docusaurus/src/client/exports/Head.tsx
+++ b/packages/docusaurus/src/client/exports/Head.tsx
@@ -8,7 +8,7 @@
 import React from 'react';
 import {Helmet} from 'react-helmet';
 
-function Head(props) {
+function Head(props): JSX.Element {
   return <Helmet {...props} />;
 }
 
diff --git a/packages/docusaurus/src/client/exports/Link.tsx b/packages/docusaurus/src/client/exports/Link.tsx
index 4d35824895b1..3a87a83742b6 100644
--- a/packages/docusaurus/src/client/exports/Link.tsx
+++ b/packages/docusaurus/src/client/exports/Link.tsx
@@ -23,7 +23,7 @@ interface Props {
   readonly href: string;
 }
 
-function Link({isNavLink, ...props}: Props) {
+function Link({isNavLink, ...props}: Props): JSX.Element {
   const {to, href} = props;
   const targetLink = to || href;
   const isInternal = isInternalUrl(targetLink);
diff --git a/packages/docusaurus/src/client/exports/Noop.ts b/packages/docusaurus/src/client/exports/Noop.ts
index 07795ed84903..385b71927fe7 100644
--- a/packages/docusaurus/src/client/exports/Noop.ts
+++ b/packages/docusaurus/src/client/exports/Noop.ts
@@ -5,4 +5,4 @@
  * LICENSE file in the root directory of this source tree.
  */
 
-export default () => null;
+export default (): null => null;
diff --git a/packages/docusaurus/src/client/exports/__tests__/useBaseUrl.ts b/packages/docusaurus/src/client/exports/__tests__/useBaseUrl.ts
index 98e96e4c4282..2529bd842647 100644
--- a/packages/docusaurus/src/client/exports/__tests__/useBaseUrl.ts
+++ b/packages/docusaurus/src/client/exports/__tests__/useBaseUrl.ts
@@ -7,6 +7,7 @@
 
 import useBaseUrl from '../useBaseUrl';
 import useDocusaurusContext from '../useDocusaurusContext';
+
 jest.mock('../useDocusaurusContext', () => jest.fn(), {virtual: true});
 
 const mockedContext = <jest.Mock>useDocusaurusContext;
diff --git a/packages/docusaurus/src/client/exports/useDocusaurusContext.ts b/packages/docusaurus/src/client/exports/useDocusaurusContext.ts
index a25bc1767d01..7dea1515aba6 100644
--- a/packages/docusaurus/src/client/exports/useDocusaurusContext.ts
+++ b/packages/docusaurus/src/client/exports/useDocusaurusContext.ts
@@ -7,8 +7,9 @@
 
 import {useContext} from 'react';
 import context from './context';
+import {DocusaurusContext} from '@docusaurus/types';
 
-function useDocusaurusContext() {
+function useDocusaurusContext(): DocusaurusContext {
   return useContext(context);
 }
 
diff --git a/packages/docusaurus/src/client/prefetch.ts b/packages/docusaurus/src/client/prefetch.ts
index fe6cc5ea67d5..4952c3431876 100644
--- a/packages/docusaurus/src/client/prefetch.ts
+++ b/packages/docusaurus/src/client/prefetch.ts
@@ -22,7 +22,7 @@ function support(feature) {
   return false;
 }
 
-function linkPrefetchStrategy(url) {
+function linkPrefetchStrategy(url: string) {
   return new Promise((resolve, reject) => {
     if (typeof document === 'undefined') {
       reject();
@@ -43,7 +43,7 @@ function linkPrefetchStrategy(url) {
   });
 }
 
-function xhrPrefetchStrategy(url) {
+function xhrPrefetchStrategy(url: string) {
   return new Promise((resolve, reject) => {
     const req = new XMLHttpRequest();
     req.open('GET', url, true);
@@ -67,7 +67,7 @@ const supportedPrefetchStrategy = support('prefetch')
 
 const preFetched = {};
 
-function prefetch(url) {
+function prefetch(url: string): Promise<void> {
   return new Promise((resolve) => {
     if (preFetched[url]) {
       resolve();
@@ -79,6 +79,7 @@ function prefetch(url) {
         resolve();
         preFetched[url] = true;
       })
+      // eslint-disable-next-line @typescript-eslint/no-empty-function
       .catch(() => {}); // 404s are logged to the console anyway.
   });
 }
diff --git a/packages/docusaurus/src/client/preload.ts b/packages/docusaurus/src/client/preload.ts
index fad0b85cbe86..092ab71a493f 100644
--- a/packages/docusaurus/src/client/preload.ts
+++ b/packages/docusaurus/src/client/preload.ts
@@ -15,7 +15,7 @@ import {matchRoutes} from 'react-router-config';
  * @param {string} pathname the route pathname, example: /docs/installation
  * @returns {Promise} Promise object represents whether pathname has been preloaded
  */
-export default function preload(routes, pathname) {
+export default function preload(routes, pathname: string) {
   const matches = matchRoutes(routes, pathname);
 
   return Promise.all(
diff --git a/packages/docusaurus/src/commands/build.ts b/packages/docusaurus/src/commands/build.ts
index 139b950037e0..29b8d6f2a558 100644
--- a/packages/docusaurus/src/commands/build.ts
+++ b/packages/docusaurus/src/commands/build.ts
@@ -36,7 +36,7 @@ function compile(config: Configuration[]): Promise<any> {
       }
       if (stats.hasWarnings()) {
         // Custom filtering warnings (see https://github.com/webpack/webpack/issues/7841).
-        let warnings = stats.toJson('errors-warnings').warnings;
+        let {warnings} = stats.toJson('errors-warnings');
         const warningsFilter = ((config[0].stats as Stats.ToJsonOptionsObject)
           ?.warningsFilter || []) as any[];
 
@@ -142,7 +142,9 @@ export async function build(
   ) {
     const serverBundle = path.join(outDir, serverConfig.output.filename);
     fs.pathExists(serverBundle).then((exist) => {
-      exist && fs.unlink(serverBundle);
+      if (exist) {
+        fs.unlink(serverBundle);
+      }
     });
   }
 
@@ -162,6 +164,8 @@ export async function build(
       relativeDir,
     )}.\n`,
   );
-  forceTerminate && !cliOptions.bundleAnalyzer && process.exit(0);
+  if (forceTerminate && !cliOptions.bundleAnalyzer) {
+    process.exit(0);
+  }
   return outDir;
 }
diff --git a/packages/docusaurus/src/commands/start.ts b/packages/docusaurus/src/commands/start.ts
index 52eb6ca8fd6e..ebe17107b720 100644
--- a/packages/docusaurus/src/commands/start.ts
+++ b/packages/docusaurus/src/commands/start.ts
@@ -5,7 +5,7 @@
  * LICENSE file in the root directory of this source tree.
  */
 
-import {normalizeUrl} from '@docusaurus/utils';
+import {normalizeUrl, posixPath} from '@docusaurus/utils';
 import chalk = require('chalk');
 import chokidar from 'chokidar';
 import express from 'express';
@@ -22,7 +22,6 @@ import merge from 'webpack-merge';
 import HotModuleReplacementPlugin from 'webpack/lib/HotModuleReplacementPlugin';
 import {load} from '../server';
 import {StartCLIOptions} from '@docusaurus/types';
-import {posixPath} from '@docusaurus/utils';
 import {CONFIG_FILE_NAME, STATIC_DIR_NAME, DEFAULT_PORT} from '../constants';
 import {createClientConfig} from '../webpack/client';
 import {applyConfigureWebpack} from '../webpack/utils';
diff --git a/packages/docusaurus/src/server/client-modules/__tests__/index.test.ts b/packages/docusaurus/src/server/client-modules/__tests__/index.test.ts
index 6964f1f3bff5..350513b56e33 100644
--- a/packages/docusaurus/src/server/client-modules/__tests__/index.test.ts
+++ b/packages/docusaurus/src/server/client-modules/__tests__/index.test.ts
@@ -7,9 +7,9 @@
 
 import {loadClientModules} from '../index';
 
-const pluginEmpty = require('./__fixtures__/plugin-empty');
-const pluginFooBar = require('./__fixtures__/plugin-foo-bar');
-const pluginHelloWorld = require('./__fixtures__/plugin-hello-world');
+import pluginEmpty from './__fixtures__/plugin-empty';
+import pluginFooBar from './__fixtures__/plugin-foo-bar';
+import pluginHelloWorld from './__fixtures__/plugin-hello-world';
 
 describe('loadClientModules', () => {
   test('empty', () => {
diff --git a/packages/docusaurus/src/server/client-modules/index.ts b/packages/docusaurus/src/server/client-modules/index.ts
index e04dba7fd54b..fc17bd57e406 100644
--- a/packages/docusaurus/src/server/client-modules/index.ts
+++ b/packages/docusaurus/src/server/client-modules/index.ts
@@ -7,7 +7,7 @@
 
 import {Plugin} from '@docusaurus/types';
 
-export function loadClientModules(plugins: Plugin<any>[]): string[] {
+export function loadClientModules(plugins: Plugin<unknown>[]): string[] {
   return ([] as string[]).concat(
     ...plugins
       .map<any>(
diff --git a/packages/docusaurus/src/server/config.ts b/packages/docusaurus/src/server/config.ts
index 1284f8ac3a46..53356f428f6d 100644
--- a/packages/docusaurus/src/server/config.ts
+++ b/packages/docusaurus/src/server/config.ts
@@ -32,10 +32,10 @@ const DEFAULT_CONFIG: {
   plugins: PluginConfig[];
   themes: PluginConfig[];
   customFields: {
-    [key: string]: any;
+    [key: string]: unknown;
   };
   themeConfig: {
-    [key: string]: any;
+    [key: string]: unknown;
   };
 } = {
   plugins: [],
diff --git a/packages/docusaurus/src/server/html-tags/__tests__/index.test.ts b/packages/docusaurus/src/server/html-tags/__tests__/index.test.ts
index 91b67dc06e79..751368320b94 100644
--- a/packages/docusaurus/src/server/html-tags/__tests__/index.test.ts
+++ b/packages/docusaurus/src/server/html-tags/__tests__/index.test.ts
@@ -7,10 +7,10 @@
 
 import {loadHtmlTags} from '../index';
 
-const pluginEmpty = require('./__fixtures__/plugin-empty');
-const pluginPreBodyTags = require('./__fixtures__/plugin-preBodyTags');
-const pluginHeadTags = require('./__fixtures__/plugin-headTags');
-const pluginPostBodyTags = require('./__fixtures__/plugin-postBodyTags');
+import pluginEmpty from './__fixtures__/plugin-empty';
+import pluginPreBodyTags from './__fixtures__/plugin-preBodyTags';
+import pluginHeadTags from './__fixtures__/plugin-headTags';
+import pluginPostBodyTags from './__fixtures__/plugin-postBodyTags';
 
 describe('loadHtmlTags', () => {
   test('empty plugin', () => {
diff --git a/packages/docusaurus/src/server/html-tags/htmlTags.ts b/packages/docusaurus/src/server/html-tags/htmlTags.ts
index 2a51e441c9c9..84d6d019b422 100644
--- a/packages/docusaurus/src/server/html-tags/htmlTags.ts
+++ b/packages/docusaurus/src/server/html-tags/htmlTags.ts
@@ -23,7 +23,7 @@ function assertIsHtmlTagObject(val: any): asserts val is HtmlTagObject {
   }
 }
 
-export function htmlTagObjectToString(tagDefinition: any): string {
+export function htmlTagObjectToString(tagDefinition: unknown): string {
   assertIsHtmlTagObject(tagDefinition);
   if (htmlTags.indexOf(tagDefinition.tagName) === -1) {
     throw new Error(
@@ -40,13 +40,9 @@ export function htmlTagObjectToString(tagDefinition: any): string {
       if (tagAttributes[attributeName] === true) {
         return attributeName;
       }
-      return attributeName + '="' + tagAttributes[attributeName] + '"';
+      return `${attributeName}="${tagAttributes[attributeName]}"`;
     });
-  return (
-    '<' +
-    [tagDefinition.tagName].concat(attributes).join(' ') +
-    '>' +
-    ((!isVoidTag && tagDefinition.innerHTML) || '') +
-    (isVoidTag ? '' : '</' + tagDefinition.tagName + '>')
-  );
+  return `<${[tagDefinition.tagName].concat(attributes).join(' ')}>${
+    (!isVoidTag && tagDefinition.innerHTML) || ''
+  }${isVoidTag ? '' : `</${tagDefinition.tagName}>`}`;
 }
diff --git a/packages/docusaurus/src/server/html-tags/index.ts b/packages/docusaurus/src/server/html-tags/index.ts
index 03c3f72ea3ec..f43e6c8d136e 100644
--- a/packages/docusaurus/src/server/html-tags/index.ts
+++ b/packages/docusaurus/src/server/html-tags/index.ts
@@ -31,13 +31,13 @@ export function loadHtmlTags(plugins: Plugin<any>[]): InjectedHtmlTags {
         plugin.injectHtmlTags() || {};
       return {
         headTags: headTags
-          ? acc.headTags + '\n' + createHtmlTagsString(headTags)
+          ? `${acc.headTags}\n${createHtmlTagsString(headTags)}`
           : acc.headTags,
         preBodyTags: preBodyTags
-          ? acc.preBodyTags + '\n' + createHtmlTagsString(preBodyTags)
+          ? `${acc.preBodyTags}\n${createHtmlTagsString(preBodyTags)}`
           : acc.preBodyTags,
         postBodyTags: postBodyTags
-          ? acc.postBodyTags + '\n' + createHtmlTagsString(postBodyTags)
+          ? `${acc.postBodyTags}\n${createHtmlTagsString(postBodyTags)}`
           : acc.postBodyTags,
       };
     },
diff --git a/packages/docusaurus/src/server/plugins/index.ts b/packages/docusaurus/src/server/plugins/index.ts
index 88c8df6dc9d8..f56eaf59eb91 100644
--- a/packages/docusaurus/src/server/plugins/index.ts
+++ b/packages/docusaurus/src/server/plugins/index.ts
@@ -17,7 +17,7 @@ import {
 } from '@docusaurus/types';
 import {initPlugins} from './init';
 
-export function sortConfig(routeConfigs: RouteConfig[]) {
+export function sortConfig(routeConfigs: RouteConfig[]): void {
   // Sort the route config. This ensures that route with nested
   // routes is always placed last.
   routeConfigs.sort((a, b) => {
@@ -55,11 +55,11 @@ export async function loadPlugins({
   pluginConfigs: PluginConfig[];
   context: LoadContext;
 }): Promise<{
-  plugins: Plugin<any>[];
+  plugins: Plugin<unknown>[];
   pluginsRouteConfigs: RouteConfig[];
 }> {
   // 1. Plugin Lifecycle - Initialization/Constructor.
-  const plugins: Plugin<any>[] = initPlugins({pluginConfigs, context});
+  const plugins: Plugin<unknown>[] = initPlugins({pluginConfigs, context});
 
   // 2. Plugin Lifecycle - loadContent.
   // Currently plugins run lifecycle methods in parallel and are not order-dependent.
@@ -71,7 +71,7 @@ export async function loadPlugins({
         return null;
       }
 
-      return await plugin.loadContent();
+      return plugin.loadContent();
     }),
   );
 
@@ -116,7 +116,7 @@ export async function loadPlugins({
         return null;
       }
 
-      return await plugin.routesLoaded(pluginsRouteConfigs);
+      return plugin.routesLoaded(pluginsRouteConfigs);
     }),
   );
 
diff --git a/packages/docusaurus/src/server/presets/index.ts b/packages/docusaurus/src/server/presets/index.ts
index 9f45f0efe2cf..7aa3ce09e536 100644
--- a/packages/docusaurus/src/server/presets/index.ts
+++ b/packages/docusaurus/src/server/presets/index.ts
@@ -29,8 +29,7 @@ export function loadPresets(
     if (typeof presetItem === 'string') {
       presetModuleImport = presetItem;
     } else if (Array.isArray(presetItem)) {
-      presetModuleImport = presetItem[0];
-      presetOptions = presetItem[1] || {};
+      [presetModuleImport, presetOptions = {}] = presetItem;
     } else {
       throw new Error('Invalid presets format detected in config.');
     }
@@ -41,8 +40,12 @@ export function loadPresets(
       presetOptions,
     );
 
-    preset.plugins && unflatPlugins.push(preset.plugins);
-    preset.themes && unflatThemes.push(preset.themes);
+    if (preset.plugins) {
+      unflatPlugins.push(preset.plugins);
+    }
+    if (preset.themes) {
+      unflatThemes.push(preset.themes);
+    }
   });
 
   return {
diff --git a/packages/docusaurus/src/server/routes.ts b/packages/docusaurus/src/server/routes.ts
index 11cb325a79ec..72abb7d8e1e3 100644
--- a/packages/docusaurus/src/server/routes.ts
+++ b/packages/docusaurus/src/server/routes.ts
@@ -18,7 +18,7 @@ import {
   ChunkNames,
 } from '@docusaurus/types';
 
-function isModule(value: any): value is Module {
+function isModule(value: unknown): value is Module {
   if (isString(value)) {
     return true;
   }
@@ -111,12 +111,11 @@ export async function loadRoutes(
       return newValue;
     }
 
-    routesChunkNames[routePath] = Object.assign(
-      {},
-      routesChunkNames[routePath],
-      genRouteChunkNames({component}, 'component', component),
-      genRouteChunkNames(modules, 'module', routePath),
-    );
+    routesChunkNames[routePath] = {
+      ...routesChunkNames[routePath],
+      ...genRouteChunkNames({component}, 'component', component),
+      ...genRouteChunkNames(modules, 'module', routePath),
+    };
 
     const routesStr = routes
       ? `routes: [${routes.map(generateRouteCode).join(',')}],`
diff --git a/packages/docusaurus/src/webpack/base.ts b/packages/docusaurus/src/webpack/base.ts
index 37ab479b5e2e..c69c2d20cfc9 100644
--- a/packages/docusaurus/src/webpack/base.ts
+++ b/packages/docusaurus/src/webpack/base.ts
@@ -21,7 +21,7 @@ const CSS_REGEX = /\.css$/;
 const CSS_MODULE_REGEX = /\.module\.css$/;
 export const clientDir = path.join(__dirname, '..', 'client');
 
-export function excludeJS(modulePath: string) {
+export function excludeJS(modulePath: string): boolean {
   // always transpile client dir
   if (modulePath.startsWith(clientDir)) {
     return false;
diff --git a/packages/docusaurus/src/webpack/plugins/ChunkAssetPlugin.ts b/packages/docusaurus/src/webpack/plugins/ChunkAssetPlugin.ts
index 8b6c0826b3e5..9876e7116db7 100644
--- a/packages/docusaurus/src/webpack/plugins/ChunkAssetPlugin.ts
+++ b/packages/docusaurus/src/webpack/plugins/ChunkAssetPlugin.ts
@@ -10,7 +10,7 @@ import {Template, Compiler} from 'webpack';
 const pluginName = 'chunk-asset-plugin';
 
 class ChunkAssetPlugin {
-  apply(compiler: Compiler) {
+  apply(compiler: Compiler): void {
     compiler.hooks.thisCompilation.tap(pluginName, ({mainTemplate}) => {
       /* We modify webpack runtime to add an extra function called "__webpack_require__.gca"
       that will allow us to get the corresponding chunk asset for a webpack chunk.
@@ -20,20 +20,21 @@ class ChunkAssetPlugin {
       mainTemplate.hooks.requireExtensions.tap(pluginName, (source, chunk) => {
         const chunkIdToName = chunk.getChunkMaps(false).name;
         const chunkNameToId = Object.create(null);
-        for (const chunkId of Object.keys(chunkIdToName)) {
+        Object.keys(chunkIdToName).forEach((chunkId) => {
           const chunkName = chunkIdToName[chunkId];
           chunkNameToId[chunkName] = chunkId;
-        }
+        });
         const buf = [source];
         buf.push('');
         buf.push('// function to get chunk assets');
         buf.push(
-          mainTemplate.requireFn +
-            // If chunkName is passed, we convert it to chunk id
-            // Note that jsonpScriptSrc is an internal webpack function
-            `.gca = function(chunkId) { chunkId = ${JSON.stringify(
-              chunkNameToId,
-            )}[chunkId]||chunkId; return jsonpScriptSrc(chunkId); };`,
+          // If chunkName is passed, we convert it to chunk id
+          // Note that jsonpScriptSrc is an internal webpack function
+          `${
+            mainTemplate.requireFn
+          }.gca = function(chunkId) { chunkId = ${JSON.stringify(
+            chunkNameToId,
+          )}[chunkId]||chunkId; return jsonpScriptSrc(chunkId); };`,
         );
         return Template.asString(buf);
       });
diff --git a/packages/docusaurus/src/webpack/plugins/CleanWebpackPlugin.ts b/packages/docusaurus/src/webpack/plugins/CleanWebpackPlugin.ts
index d5c397c718fc..2c34d4f92bda 100644
--- a/packages/docusaurus/src/webpack/plugins/CleanWebpackPlugin.ts
+++ b/packages/docusaurus/src/webpack/plugins/CleanWebpackPlugin.ts
@@ -180,7 +180,7 @@ class CleanWebpackPlugin {
     this.removeFiles = this.removeFiles.bind(this);
   }
 
-  apply(compiler: Compiler) {
+  apply(compiler: Compiler): void {
     if (!compiler.options.output || !compiler.options.output.path) {
       // eslint-disable-next-line no-console
       console.warn(
@@ -197,7 +197,7 @@ class CleanWebpackPlugin {
      *
      * Check for hooks in-order to support old plugin system
      */
-    const hooks = compiler.hooks;
+    const {hooks} = compiler;
 
     if (this.cleanOnceBeforeBuildPatterns.length !== 0) {
       if (hooks) {
@@ -229,7 +229,7 @@ class CleanWebpackPlugin {
    *
    * Warning: It is recommended to initially clean your build directory outside of webpack to minimize unexpected behavior.
    */
-  handleInitial() {
+  handleInitial(): void {
     if (this.initialClean) {
       return;
     }
@@ -239,7 +239,7 @@ class CleanWebpackPlugin {
     this.removeFiles(this.cleanOnceBeforeBuildPatterns);
   }
 
-  handleDone(stats: Stats) {
+  handleDone(stats: Stats): void {
     /**
      * Do nothing if there is a webpack error
      */
@@ -304,7 +304,7 @@ class CleanWebpackPlugin {
     }
   }
 
-  removeFiles(patterns: string[]) {
+  removeFiles(patterns: string[]): void {
     try {
       const deleted = delSync(patterns, {
         force: this.dangerouslyAllowCleanPatternsOutsideProject,
diff --git a/packages/docusaurus/src/webpack/utils.ts b/packages/docusaurus/src/webpack/utils.ts
index 111e40998009..b6c5a747a190 100644
--- a/packages/docusaurus/src/webpack/utils.ts
+++ b/packages/docusaurus/src/webpack/utils.ts
@@ -53,6 +53,7 @@ export function getStyleLoaders(
         // https://github.com/facebook/create-react-app/issues/2677
         ident: 'postcss',
         plugins: () => [
+          // eslint-disable-next-line @typescript-eslint/no-var-requires
           require('postcss-preset-env')({
             autoprefixer: {
               flexbox: 'no-2009',
@@ -76,12 +77,10 @@ export function getCacheLoader(
 
   return {
     loader: require.resolve('cache-loader'),
-    options: Object.assign(
-      {
-        cacheIdentifier: `cache-loader:${cacheLoaderVersion}${isServer}`,
-      },
-      cacheOptions,
-    ),
+    options: {
+      cacheIdentifier: `cache-loader:${cacheLoaderVersion}${isServer}`,
+      ...cacheOptions,
+    },
   };
 }
 
diff --git a/packages/lqip-loader/src/__tests__/index.test.ts b/packages/lqip-loader/src/__tests__/index.test.ts
index 8f9e416d8434..b48f08b801e7 100644
--- a/packages/lqip-loader/src/__tests__/index.test.ts
+++ b/packages/lqip-loader/src/__tests__/index.test.ts
@@ -32,8 +32,8 @@ describe('lqip-loader', () => {
       const vibrant = new Vibrant(imgPath, {});
 
       return vibrant.getPalette().then((palette) => {
-        correctTestSwatch = Object.assign({}, palette);
-        testSwatchWithNull = Object.assign({}, palette, {Vibrant: null});
+        correctTestSwatch = {...palette};
+        testSwatchWithNull = {...palette, Vibrant: null};
       });
     });