diff --git a/packages/docusaurus-types/src/index.d.ts b/packages/docusaurus-types/src/index.d.ts
index 28eddd1963..2dbdc89b1c 100644
--- a/packages/docusaurus-types/src/index.d.ts
+++ b/packages/docusaurus-types/src/index.d.ts
@@ -45,6 +45,7 @@ export interface DocusaurusConfig {
 
 export interface DocusaurusContext {
   siteConfig?: DocusaurusConfig;
+  isClient?: boolean;
 }
 
 export interface Preset {
diff --git a/packages/docusaurus/copyUntypedFiles.js b/packages/docusaurus/copyUntypedFiles.js
index 3f814cf099..e5555c5536 100644
--- a/packages/docusaurus/copyUntypedFiles.js
+++ b/packages/docusaurus/copyUntypedFiles.js
@@ -15,6 +15,6 @@ const srcDir = path.resolve(__dirname, 'src');
 const libDir = path.resolve(__dirname, 'lib');
 fs.copySync(srcDir, libDir, {
   filter(filepath) {
-    return !/__tests__/.test(filepath) && !/\.ts$/.test(filepath);
+    return !/__tests__/.test(filepath) && !/\.tsx?$/.test(filepath);
   },
 });
diff --git a/packages/docusaurus/package.json b/packages/docusaurus/package.json
index e659101a16..deaf509391 100644
--- a/packages/docusaurus/package.json
+++ b/packages/docusaurus/package.json
@@ -23,7 +23,7 @@
     "docusaurus": "bin/docusaurus.js"
   },
   "scripts": {
-    "tsc": "tsc && node copyUntypedFiles.js"
+    "tsc": "tsc && tsc -p tsconfig.client.json && node copyUntypedFiles.js"
   },
   "bugs": {
     "url": "https://github.com/facebook/docusaurus/issues"
diff --git a/packages/docusaurus/src/client/App.js b/packages/docusaurus/src/client/App.tsx
similarity index 88%
rename from packages/docusaurus/src/client/App.js
rename to packages/docusaurus/src/client/App.tsx
index abf2bae837..40d4f42491 100644
--- a/packages/docusaurus/src/client/App.js
+++ b/packages/docusaurus/src/client/App.tsx
@@ -9,8 +9,8 @@ import React, {useEffect, useState} from 'react';
 
 import routes from '@generated/routes';
 import siteConfig from '@generated/docusaurus.config';
-import renderRoutes from '@docusaurus/renderRoutes';
-import DocusaurusContext from '@docusaurus/context';
+import renderRoutes from './exports/renderRoutes';
+import DocusaurusContext from './exports/context';
 import PendingNavigation from './PendingNavigation';
 
 import './client-lifecycles-dispatcher';
diff --git a/packages/docusaurus/src/client/PendingNavigation.js b/packages/docusaurus/src/client/PendingNavigation.tsx
similarity index 92%
rename from packages/docusaurus/src/client/PendingNavigation.js
rename to packages/docusaurus/src/client/PendingNavigation.tsx
index f5316d8b64..63f623eadf 100644
--- a/packages/docusaurus/src/client/PendingNavigation.js
+++ b/packages/docusaurus/src/client/PendingNavigation.tsx
@@ -17,8 +17,20 @@ import 'nprogress/nprogress.css';
 
 nprogress.configure({showSpinner: false});
 
-class PendingNavigation extends React.Component {
-  constructor(props) {
+interface Props {
+  routes: any[];
+  delay: number;
+  location: any;
+}
+interface State {
+  nextRouteHasLoaded: boolean;
+}
+
+class PendingNavigation extends React.Component<Props, State> {
+  previousLocation: any;
+  progressBarTimeout: any;
+
+  constructor(props: Props) {
     super(props);
 
     // previousLocation doesn't affect rendering, hence not stored in state.
diff --git a/packages/docusaurus/src/client/__tests__/flat.test.js b/packages/docusaurus/src/client/__tests__/flat.test.ts
similarity index 100%
rename from packages/docusaurus/src/client/__tests__/flat.test.js
rename to packages/docusaurus/src/client/__tests__/flat.test.ts
diff --git a/packages/docusaurus/src/client/__tests__/normalizeLocation.test.js b/packages/docusaurus/src/client/__tests__/normalizeLocation.test.ts
similarity index 100%
rename from packages/docusaurus/src/client/__tests__/normalizeLocation.test.js
rename to packages/docusaurus/src/client/__tests__/normalizeLocation.test.ts
diff --git a/packages/docusaurus/src/client/client-lifecycles-dispatcher.js b/packages/docusaurus/src/client/client-lifecycles-dispatcher.ts
similarity index 87%
rename from packages/docusaurus/src/client/client-lifecycles-dispatcher.js
rename to packages/docusaurus/src/client/client-lifecycles-dispatcher.ts
index 942dd3c2af..376b228664 100644
--- a/packages/docusaurus/src/client/client-lifecycles-dispatcher.js
+++ b/packages/docusaurus/src/client/client-lifecycles-dispatcher.ts
@@ -16,7 +16,12 @@ function dispatchLifecycleAction(lifecycleAction, ...args) {
   });
 }
 
-function createLifecyclesDispatcher() {
+interface Dispatchers {
+  onRouteUpdate: Function;
+  onRouteUpdateDelayed: Function;
+}
+
+function createLifecyclesDispatcher(): Dispatchers {
   // TODO: Not sure whether it's better to declare an explicit object
   // with all the lifecycles. It's better for typing but quite verbose.
   // On the other hand, there's some runtime cost generating this object
@@ -30,7 +35,7 @@ function createLifecyclesDispatcher() {
       return lifecycles;
     },
     {},
-  );
+  ) as Dispatchers;
 }
 
 export default createLifecyclesDispatcher();
diff --git a/packages/docusaurus/src/client/clientEntry.js b/packages/docusaurus/src/client/clientEntry.tsx
similarity index 91%
rename from packages/docusaurus/src/client/clientEntry.js
rename to packages/docusaurus/src/client/clientEntry.tsx
index 51e2a2ef3f..ce733a4e7a 100644
--- a/packages/docusaurus/src/client/clientEntry.js
+++ b/packages/docusaurus/src/client/clientEntry.tsx
@@ -10,11 +10,17 @@ import {hydrate, render} from 'react-dom';
 import {BrowserRouter} from 'react-router-dom';
 
 import routes from '@generated/routes';
-import ExecutionEnvironment from '@docusaurus/ExecutionEnvironment';
+import ExecutionEnvironment from './exports/ExecutionEnvironment';
 import App from './App';
 import preload from './preload';
 import docusaurus from './docusaurus';
 
+declare global {
+  interface NodeModule {
+    hot?: any;
+  }
+}
+
 // Client-side render (e.g: running in browser) to become single-page application (SPA).
 if (ExecutionEnvironment.canUseDOM) {
   window.docusaurus = docusaurus;
diff --git a/packages/docusaurus/src/client/docusaurus.js b/packages/docusaurus/src/client/docusaurus.ts
similarity index 95%
rename from packages/docusaurus/src/client/docusaurus.js
rename to packages/docusaurus/src/client/docusaurus.ts
index 17ca22ae77..2bbe88de34 100644
--- a/packages/docusaurus/src/client/docusaurus.js
+++ b/packages/docusaurus/src/client/docusaurus.ts
@@ -14,6 +14,13 @@ import flat from './flat';
 const fetched = {};
 const loaded = {};
 
+declare global {
+  const __webpack_require__: any;
+  interface Navigator {
+    connection: any;
+  }
+}
+
 const isSlowConnection = () => {
   // If user is on slow or constrained connection.
   if (`connection` in navigator) {
diff --git a/packages/docusaurus/src/client/exports/BrowserOnly.js b/packages/docusaurus/src/client/exports/BrowserOnly.tsx
similarity index 84%
rename from packages/docusaurus/src/client/exports/BrowserOnly.js
rename to packages/docusaurus/src/client/exports/BrowserOnly.tsx
index ddae8bb3eb..5c39340b12 100644
--- a/packages/docusaurus/src/client/exports/BrowserOnly.js
+++ b/packages/docusaurus/src/client/exports/BrowserOnly.tsx
@@ -6,7 +6,7 @@
  */
 
 import React from 'react';
-import ExecutionEnvironment from '@docusaurus/ExecutionEnvironment';
+import ExecutionEnvironment from './ExecutionEnvironment';
 
 function BrowserOnly({children}) {
   return (
diff --git a/packages/docusaurus/src/client/exports/ComponentCreator.js b/packages/docusaurus/src/client/exports/ComponentCreator.tsx
similarity index 95%
rename from packages/docusaurus/src/client/exports/ComponentCreator.js
rename to packages/docusaurus/src/client/exports/ComponentCreator.tsx
index 485c86651f..1ee17d0315 100644
--- a/packages/docusaurus/src/client/exports/ComponentCreator.js
+++ b/packages/docusaurus/src/client/exports/ComponentCreator.tsx
@@ -12,7 +12,7 @@ import routesChunkNames from '@generated/routesChunkNames';
 import registry from '@generated/registry';
 import flat from '../flat';
 
-function ComponentCreator(path) {
+function ComponentCreator(path: string) {
   // 404 page
   if (path === '*') {
     return Loadable({
@@ -22,8 +22,8 @@ function ComponentCreator(path) {
   }
 
   const chunkNames = routesChunkNames[path];
-  const optsModules = [];
-  const optsWebpack = [];
+  const optsModules: string[] = [];
+  const optsWebpack: string[] = [];
   const optsLoader = {};
 
   /* Prepare opts data that react-loadable needs
diff --git a/packages/docusaurus/src/client/exports/ExecutionEnvironment.js b/packages/docusaurus/src/client/exports/ExecutionEnvironment.ts
similarity index 91%
rename from packages/docusaurus/src/client/exports/ExecutionEnvironment.js
rename to packages/docusaurus/src/client/exports/ExecutionEnvironment.ts
index 91867c8aa9..9509054616 100644
--- a/packages/docusaurus/src/client/exports/ExecutionEnvironment.js
+++ b/packages/docusaurus/src/client/exports/ExecutionEnvironment.ts
@@ -15,6 +15,7 @@ const ExecutionEnvironment = {
   canUseDOM,
 
   canUseEventListeners:
+    // @ts-ignore
     canUseDOM && !!(window.addEventListener || window.attachEvent),
 
   canUseIntersectionObserver: canUseDOM && 'IntersectionObserver' in window,
@@ -22,4 +23,4 @@ const ExecutionEnvironment = {
   canUseViewport: canUseDOM && !!window.screen,
 };
 
-module.exports = ExecutionEnvironment;
+export default ExecutionEnvironment;
diff --git a/packages/docusaurus/src/client/exports/Head.js b/packages/docusaurus/src/client/exports/Head.tsx
similarity index 100%
rename from packages/docusaurus/src/client/exports/Head.js
rename to packages/docusaurus/src/client/exports/Head.tsx
diff --git a/packages/docusaurus/src/client/exports/Link.js b/packages/docusaurus/src/client/exports/Link.tsx
similarity index 87%
rename from packages/docusaurus/src/client/exports/Link.js
rename to packages/docusaurus/src/client/exports/Link.tsx
index f3a978f7ff..ec970aa43c 100644
--- a/packages/docusaurus/src/client/exports/Link.js
+++ b/packages/docusaurus/src/client/exports/Link.tsx
@@ -6,11 +6,24 @@
  */
 
 import React, {useEffect, useRef} from 'react';
-import {NavLink, Link as RRLink} from 'react-router-dom';
-import isInternalUrl from '@docusaurus/isInternalUrl';
-import ExecutionEnvironment from '@docusaurus/ExecutionEnvironment';
 
-function Link({isNavLink, ...props}) {
+import {NavLink, Link as RRLink} from 'react-router-dom';
+import isInternalUrl from './isInternalUrl';
+import ExecutionEnvironment from './ExecutionEnvironment';
+
+declare global {
+  interface Window {
+    docusaurus: any;
+  }
+}
+
+interface Props {
+  readonly isNavLink?: boolean;
+  readonly to?: string;
+  readonly href: string
+}
+
+function Link({isNavLink, ...props}: Props) {
   const {to, href} = props;
   const targetLink = to || href;
   const isInternal = isInternalUrl(targetLink);
diff --git a/packages/docusaurus/src/client/exports/Noop.js b/packages/docusaurus/src/client/exports/Noop.ts
similarity index 100%
rename from packages/docusaurus/src/client/exports/Noop.js
rename to packages/docusaurus/src/client/exports/Noop.ts
diff --git a/packages/docusaurus/src/client/exports/context.js b/packages/docusaurus/src/client/exports/context.ts
similarity index 66%
rename from packages/docusaurus/src/client/exports/context.js
rename to packages/docusaurus/src/client/exports/context.ts
index b979a7f1f7..d5b4f3c5c2 100644
--- a/packages/docusaurus/src/client/exports/context.js
+++ b/packages/docusaurus/src/client/exports/context.ts
@@ -6,5 +6,6 @@
  */
 
 import React from 'react';
+import {DocusaurusContext} from '@docusaurus/types';
 
-export default React.createContext({});
+export default React.createContext<DocusaurusContext>({});
diff --git a/packages/docusaurus/src/client/exports/isInternalUrl.js b/packages/docusaurus/src/client/exports/isInternalUrl.ts
similarity index 80%
rename from packages/docusaurus/src/client/exports/isInternalUrl.js
rename to packages/docusaurus/src/client/exports/isInternalUrl.ts
index 9e7acfc818..c68ce38be6 100644
--- a/packages/docusaurus/src/client/exports/isInternalUrl.js
+++ b/packages/docusaurus/src/client/exports/isInternalUrl.ts
@@ -5,6 +5,6 @@
  * LICENSE file in the root directory of this source tree.
  */
 
-export default function isInternalUrl(url) {
+export default function isInternalUrl(url: string): boolean {
   return /^(https?:|\/\/|mailto:|tel:)/.test(url) === false;
 }
diff --git a/packages/docusaurus/src/client/exports/renderRoutes.js b/packages/docusaurus/src/client/exports/renderRoutes.ts
similarity index 100%
rename from packages/docusaurus/src/client/exports/renderRoutes.js
rename to packages/docusaurus/src/client/exports/renderRoutes.ts
diff --git a/packages/docusaurus/src/client/exports/router.js b/packages/docusaurus/src/client/exports/router.ts
similarity index 100%
rename from packages/docusaurus/src/client/exports/router.js
rename to packages/docusaurus/src/client/exports/router.ts
diff --git a/packages/docusaurus/src/client/exports/useBaseUrl.js b/packages/docusaurus/src/client/exports/useBaseUrl.ts
similarity index 90%
rename from packages/docusaurus/src/client/exports/useBaseUrl.js
rename to packages/docusaurus/src/client/exports/useBaseUrl.ts
index aed661096b..a27d87813c 100644
--- a/packages/docusaurus/src/client/exports/useBaseUrl.js
+++ b/packages/docusaurus/src/client/exports/useBaseUrl.ts
@@ -7,7 +7,7 @@
 
 import useDocusaurusContext from './useDocusaurusContext';
 
-export default function useBaseUrl(url) {
+export default function useBaseUrl(url: string): string {
   const {siteConfig} = useDocusaurusContext();
   const {baseUrl = '/'} = siteConfig || {};
 
diff --git a/packages/docusaurus/src/client/exports/useDocusaurusContext.js b/packages/docusaurus/src/client/exports/useDocusaurusContext.ts
similarity index 100%
rename from packages/docusaurus/src/client/exports/useDocusaurusContext.js
rename to packages/docusaurus/src/client/exports/useDocusaurusContext.ts
diff --git a/packages/docusaurus/src/client/flat.js b/packages/docusaurus/src/client/flat.ts
similarity index 94%
rename from packages/docusaurus/src/client/flat.js
rename to packages/docusaurus/src/client/flat.ts
index 04173df589..b1f320b3ab 100644
--- a/packages/docusaurus/src/client/flat.js
+++ b/packages/docusaurus/src/client/flat.ts
@@ -9,7 +9,7 @@ function flat(target) {
   const delimiter = '.';
   const output = {};
 
-  function step(object, prev) {
+  function step(object, prev?: string) {
     Object.keys(object).forEach((key) => {
       const value = object[key];
       const type = typeof value;
diff --git a/packages/docusaurus/src/client/normalizeLocation.js b/packages/docusaurus/src/client/normalizeLocation.ts
similarity index 100%
rename from packages/docusaurus/src/client/normalizeLocation.js
rename to packages/docusaurus/src/client/normalizeLocation.ts
diff --git a/packages/docusaurus/src/client/prefetch.js b/packages/docusaurus/src/client/prefetch.ts
similarity index 100%
rename from packages/docusaurus/src/client/prefetch.js
rename to packages/docusaurus/src/client/prefetch.ts
diff --git a/packages/docusaurus/src/client/preload.js b/packages/docusaurus/src/client/preload.ts
similarity index 100%
rename from packages/docusaurus/src/client/preload.js
rename to packages/docusaurus/src/client/preload.ts
diff --git a/packages/docusaurus/src/client/serverEntry.js b/packages/docusaurus/src/client/serverEntry.js
index 5cb7be8d57..b700e41aa6 100644
--- a/packages/docusaurus/src/client/serverEntry.js
+++ b/packages/docusaurus/src/client/serverEntry.js
@@ -18,7 +18,9 @@ import path from 'path';
 import fs from 'fs-extra';
 import routes from '@generated/routes';
 import packageJson from '../../package.json';
+// eslint-disable-next-line import/no-unresolved
 import preload from './preload';
+// eslint-disable-next-line import/no-unresolved
 import App from './App';
 import ssrTemplate from './templates/ssr.html.template';
 
diff --git a/packages/docusaurus/src/client/types.d.ts b/packages/docusaurus/src/client/types.d.ts
new file mode 100644
index 0000000000..4d019518ae
--- /dev/null
+++ b/packages/docusaurus/src/client/types.d.ts
@@ -0,0 +1,43 @@
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+declare module '@generated/client-modules' {
+  const clientModules: readonly any[];
+  export default clientModules;
+}
+
+declare module '@generated/docusaurus.config' {
+  const config: any;
+  export default config;
+}
+
+declare module '@generated/registry' {
+  const registry: {
+    readonly [key: string]: [() => Promise<any>, string, string];
+  };
+  export default registry;
+}
+
+declare module '@generated/routes' {
+  type Route = {
+    readonly path: string;
+    readonly component: any;
+    readonly exact?: boolean;
+  };
+  const routes: Route[];
+  export default routes;
+}
+
+declare module '@generated/routesChunkNames' {
+  const routesChunkNames: any;
+  export default routesChunkNames;
+}
+
+declare module '@theme/*' {
+  const component: any;
+  export default component;
+}
diff --git a/packages/docusaurus/tsconfig.client.json b/packages/docusaurus/tsconfig.client.json
new file mode 100644
index 0000000000..713d7753e9
--- /dev/null
+++ b/packages/docusaurus/tsconfig.client.json
@@ -0,0 +1,13 @@
+{
+  "extends": "../../tsconfig.json",
+  "compilerOptions": {
+    "incremental": true,
+    "lib": ["DOM"],
+    "module": "esnext",
+    "tsBuildInfoFile": "./lib/client/.tsbuildinfo",
+    "outDir": "lib/client",
+    "noImplicitAny": false,
+    "jsx": "react",
+  },
+  "include": ["src/client"]
+}
diff --git a/packages/docusaurus/tsconfig.json b/packages/docusaurus/tsconfig.json
index ef724a2c34..5276f6f4d1 100644
--- a/packages/docusaurus/tsconfig.json
+++ b/packages/docusaurus/tsconfig.json
@@ -2,10 +2,12 @@
   "extends": "../../tsconfig.json",
   "compilerOptions": {
     "incremental": true,
+    "lib": ["DOM"],
     "tsBuildInfoFile": "./lib/.tsbuildinfo",
     "rootDir": "src",
     "outDir": "lib",
     "noImplicitAny": false,
     "jsx": "react",
   },
+  "exclude": ["node_modules", "**/__tests__/**/*", "**/lib/**/*", "src/client"]
 }