diff --git a/app/config.js b/app/config.ts
similarity index 87%
rename from app/config.js
rename to app/config.ts
index 06bb119d..dfb8d572 100644
--- a/app/config.js
+++ b/app/config.ts
@@ -6,9 +6,32 @@ import win from './config/windows';
 import {cfgPath, cfgDir} from './config/paths';
 import {getColorMap} from './utils/colors';
 
-const watchers = [];
-let cfg = {};
-let _watcher;
+const watchers: any[] = [];
+let cfg: Record<string, any> = {};
+let _watcher: fs.FSWatcher;
+
+export const getDeprecatedCSS = (config: Record<string, any>) => {
+  const deprecated: string[] = [];
+  const deprecatedCSS = ['x-screen', 'x-row', 'cursor-node', '::selection'];
+  deprecatedCSS.forEach(css => {
+    if ((config.css && config.css.includes(css)) || (config.termCSS && config.termCSS.includes(css))) {
+      deprecated.push(css);
+    }
+  });
+  return deprecated;
+};
+
+const checkDeprecatedConfig = () => {
+  if (!cfg.config) {
+    return;
+  }
+  const deprecated = getDeprecatedCSS(cfg.config);
+  if (deprecated.length === 0) {
+    return;
+  }
+  const deprecatedStr = deprecated.join(', ');
+  notify('Configuration warning', `Your configuration uses some deprecated CSS classes (${deprecatedStr})`);
+};
 
 const _watch = () => {
   if (_watcher) {
@@ -36,11 +59,10 @@ const _watch = () => {
       } else if (curr.mtime.getTime() !== prev.mtime.getTime()) {
         onChange();
       }
-    });
+    }) as any;
     return;
   }
   // macOS/Linux
-  setWatcher();
   function setWatcher() {
     try {
       _watcher = fs.watch(cfgPath, eventType => {
@@ -61,9 +83,10 @@ const _watch = () => {
       console.error('error watching config', error);
     });
   }
+  setWatcher();
 };
 
-export const subscribe = fn => {
+export const subscribe = (fn: Function) => {
   watchers.push(fn);
   return () => {
     watchers.splice(watchers.indexOf(fn), 1);
@@ -83,7 +106,7 @@ export const openConfig = () => {
   return _openConfig();
 };
 
-export const getPlugins = () => {
+export const getPlugins = (): {plugins: string[]; localPlugins: string[]} => {
   return {
     plugins: cfg.plugins,
     localPlugins: cfg.localPlugins
@@ -104,40 +127,16 @@ export const getWin = win.get;
 export const winRecord = win.recordState;
 export const windowDefaults = win.defaults;
 
-const getDeprecatedCSS = config => {
-  const deprecated = [];
-  const deprecatedCSS = ['x-screen', 'x-row', 'cursor-node', '::selection'];
-  deprecatedCSS.forEach(css => {
-    if ((config.css && config.css.includes(css)) || (config.termCSS && config.termCSS.includes(css))) {
-      deprecated.push(css);
-    }
-  });
-  return deprecated;
-};
-export {getDeprecatedCSS};
-
-const checkDeprecatedConfig = () => {
-  if (!cfg.config) {
-    return;
-  }
-  const deprecated = getDeprecatedCSS(cfg.config);
-  if (deprecated.length === 0) {
-    return;
-  }
-  const deprecatedStr = deprecated.join(', ');
-  notify('Configuration warning', `Your configuration uses some deprecated CSS classes (${deprecatedStr})`);
-};
-
-export const fixConfigDefaults = decoratedConfig => {
-  const defaultConfig = getDefaultConfig().config;
+export const fixConfigDefaults = (decoratedConfig: any) => {
+  const defaultConfig = getDefaultConfig()?.config;
   decoratedConfig.colors = getColorMap(decoratedConfig.colors) || {};
   // We must have default colors for xterm css.
   decoratedConfig.colors = Object.assign({}, defaultConfig.colors, decoratedConfig.colors);
   return decoratedConfig;
 };
 
-export const htermConfigTranslate = config => {
-  const cssReplacements = {
+export const htermConfigTranslate = (config: Record<string, any>) => {
+  const cssReplacements: Record<string, string> = {
     'x-screen x-row([ {.[])': '.xterm-rows > div$1',
     '.cursor-node([ {.[])': '.terminal-cursor$1',
     '::selection([ {.[])': '.terminal .xterm-selection div$1',
diff --git a/app/ext-modules.d.ts b/app/ext-modules.d.ts
index cbe6f667..443d58ee 100644
--- a/app/ext-modules.d.ts
+++ b/app/ext-modules.d.ts
@@ -1,3 +1,8 @@
 declare module 'git-describe' {
   export function gitDescribe(...args: any[]): void;
 }
+
+declare module 'default-shell' {
+  const val: string;
+  export default val;
+}
diff --git a/app/notifications.js b/app/notifications.ts
similarity index 84%
rename from app/notifications.js
rename to app/notifications.ts
index 0167489b..0a92cc36 100644
--- a/app/notifications.js
+++ b/app/notifications.ts
@@ -1,12 +1,13 @@
 import ms from 'ms';
 import fetch from 'electron-fetch';
-import {version} from './package';
+import {version} from './package.json';
+import {BrowserWindow} from 'electron';
 
 const NEWS_URL = 'https://hyper-news.now.sh';
 
-export default function fetchNotifications(win) {
+export default function fetchNotifications(win: BrowserWindow) {
   const {rpc} = win;
-  const retry = err => {
+  const retry = (err?: any) => {
     setTimeout(() => fetchNotifications(win), ms('30m'));
     if (err) {
       //eslint-disable-next-line no-console
diff --git a/app/notify.js b/app/notify.ts
similarity index 88%
rename from app/notify.js
rename to app/notify.ts
index b003397f..8c63a8e2 100644
--- a/app/notify.js
+++ b/app/notify.ts
@@ -2,14 +2,28 @@ import {resolve} from 'path';
 import {app, BrowserWindow} from 'electron';
 import isDev from 'electron-is-dev';
 
-let win;
+let win: BrowserWindow;
 
 // the hack of all hacks
 // electron doesn't have a built in notification thing,
 // so we launch a window on which we can use the
 // HTML5 `Notification` API :'(
 
-let buffer = [];
+let buffer: string[][] = [];
+
+function notify(title: string, body = '', details: any = {}) {
+  //eslint-disable-next-line no-console
+  console.log(`[Notification] ${title}: ${body}`);
+  if (details.error) {
+    //eslint-disable-next-line no-console
+    console.error(details.error);
+  }
+  if (win) {
+    win.webContents.send('notification', {title, body});
+  } else {
+    buffer.push([title, body]);
+  }
+}
 
 app.on('ready', () => {
   const win_ = new BrowserWindow({
@@ -25,22 +39,8 @@ app.on('ready', () => {
     buffer.forEach(([title, body]) => {
       notify(title, body);
     });
-    buffer = null;
+    buffer = [];
   });
 });
 
-function notify(title, body, details = {}) {
-  //eslint-disable-next-line no-console
-  console.log(`[Notification] ${title}: ${body}`);
-  if (details.error) {
-    //eslint-disable-next-line no-console
-    console.error(details.error);
-  }
-  if (win) {
-    win.webContents.send('notification', {title, body});
-  } else {
-    buffer.push([title, body]);
-  }
-}
-
 export default notify;
diff --git a/app/plugins.js b/app/plugins.ts
similarity index 87%
rename from app/plugins.js
rename to app/plugins.ts
index 98277929..da62f360 100644
--- a/app/plugins.js
+++ b/app/plugins.ts
@@ -1,4 +1,5 @@
-import {app, dialog} from 'electron';
+/* eslint-disable @typescript-eslint/no-use-before-define */
+import {app, dialog, BrowserWindow, App} from 'electron';
 import {resolve, basename} from 'path';
 import {writeFileSync} from 'fs';
 import Config from 'electron-store';
@@ -26,11 +27,11 @@ let paths = getPaths();
 let id = getId(plugins);
 let modules = requirePlugins();
 
-function getId(plugins_) {
+function getId(plugins_: any) {
   return JSON.stringify(plugins_);
 }
 
-const watchers = [];
+const watchers: Function[] = [];
 
 // we listen on configuration updates to trigger
 // plugin installation
@@ -50,9 +51,10 @@ config.subscribe(() => {
 // so plugins can `require` them without needing their own version
 // https://github.com/zeit/hyper/issues/619
 function patchModuleLoad() {
+  // eslint-disable-next-line @typescript-eslint/no-var-requires
   const Module = require('module');
   const originalLoad = Module._load;
-  Module._load = function _load(modulePath) {
+  Module._load = function _load(modulePath: string) {
     // PLEASE NOTE: Code changes here, also need to be changed in
     // lib/utils/plugins.js
     switch (modulePath) {
@@ -72,6 +74,7 @@ function patchModuleLoad() {
       case 'hyper/decorate':
         return Object;
       default:
+        // eslint-disable-next-line prefer-rest-params
         return originalLoad.apply(this, arguments);
     }
   };
@@ -95,7 +98,7 @@ function updatePlugins({force = false} = {}) {
   updating = true;
   syncPackageJSON();
   const id_ = id;
-  install(err => {
+  install((err: any) => {
     updating = false;
 
     if (err) {
@@ -185,7 +188,10 @@ if (cache.get('hyper.plugins') !== id || process.env.HYPER_FORCE_UPDATE) {
   const baseConfig = config.getConfig();
   if (baseConfig['autoUpdatePlugins']) {
     // otherwise update plugins every 5 hours
-    setInterval(updatePlugins, ms(baseConfig['autoUpdatePlugins'] === true ? '5h' : baseConfig['autoUpdatePlugins']));
+    setInterval(
+      updatePlugins,
+      ms(baseConfig['autoUpdatePlugins'] === true ? '5h' : (baseConfig['autoUpdatePlugins'] as string))
+    );
   }
 })();
 
@@ -210,15 +216,15 @@ function syncPackageJSON() {
   }
 }
 
-function alert(message) {
+function alert(message: string) {
   dialog.showMessageBox({
     message,
     buttons: ['Ok']
   });
 }
 
-function toDependencies(plugins_) {
-  const obj = {};
+function toDependencies(plugins_: {plugins: string[]}) {
+  const obj: Record<string, string> = {};
   plugins_.plugins.forEach(plugin => {
     const regex = /.(@|#)/;
     const match = regex.exec(plugin);
@@ -237,7 +243,7 @@ function toDependencies(plugins_) {
   return obj;
 }
 
-export const subscribe = fn => {
+export const subscribe = (fn: Function) => {
   watchers.push(fn);
   return () => {
     watchers.splice(watchers.indexOf(fn), 1);
@@ -263,11 +269,11 @@ export const getBasePaths = () => {
   return {path, localPath};
 };
 
-function requirePlugins() {
+function requirePlugins(): any[] {
   const {plugins: plugins_, localPlugins} = paths;
 
-  const load = path_ => {
-    let mod;
+  const load = (path_: string) => {
+    let mod: any;
     try {
       mod = require(path_);
       const exposed = mod && Object.keys(mod).some(key => availableExtensions.has(key));
@@ -304,7 +310,7 @@ function requirePlugins() {
     .filter(v => Boolean(v));
 }
 
-export const onApp = app_ => {
+export const onApp = (app_: App) => {
   modules.forEach(plugin => {
     if (plugin.onApp) {
       try {
@@ -318,7 +324,7 @@ export const onApp = app_ => {
   });
 };
 
-export const onWindowClass = win => {
+export const onWindowClass = (win: BrowserWindow) => {
   modules.forEach(plugin => {
     if (plugin.onWindowClass) {
       try {
@@ -332,7 +338,7 @@ export const onWindowClass = win => {
   });
 };
 
-export const onWindow = win => {
+export const onWindow = (win: BrowserWindow) => {
   modules.forEach(plugin => {
     if (plugin.onWindow) {
       try {
@@ -348,7 +354,7 @@ export const onWindow = win => {
 
 // decorates the base entity by calling plugin[key]
 // for all the available plugins
-function decorateEntity(base, key, type) {
+function decorateEntity(base: any, key: string, type: 'object' | 'function') {
   let decorated = base;
   modules.forEach(plugin => {
     if (plugin[key]) {
@@ -370,16 +376,16 @@ function decorateEntity(base, key, type) {
   return decorated;
 }
 
-function decorateObject(base, key) {
+function decorateObject(base: any, key: string) {
   return decorateEntity(base, key, 'object');
 }
 
-function decorateClass(base, key) {
+function decorateClass(base: any, key: string) {
   return decorateEntity(base, key, 'function');
 }
 
 export const getDeprecatedConfig = () => {
-  const deprecated = {};
+  const deprecated: Record<string, any> = {};
   const baseConfig = config.getConfig();
   modules.forEach(plugin => {
     if (!plugin.decorateConfig) {
@@ -404,11 +410,11 @@ export const getDeprecatedConfig = () => {
   return deprecated;
 };
 
-export const decorateMenu = tpl => {
+export const decorateMenu = (tpl: any) => {
   return decorateObject(tpl, 'decorateMenu');
 };
 
-export const getDecoratedEnv = baseEnv => {
+export const getDecoratedEnv = (baseEnv: Record<string, string>) => {
   return decorateObject(baseEnv, 'decorateEnv');
 };
 
@@ -427,19 +433,19 @@ export const getDecoratedKeymaps = () => {
   return decoratedKeymaps;
 };
 
-export const getDecoratedBrowserOptions = defaults => {
+export const getDecoratedBrowserOptions = <T>(defaults: T): T => {
   return decorateObject(defaults, 'decorateBrowserOptions');
 };
 
-export const decorateWindowClass = defaults => {
+export const decorateWindowClass = <T>(defaults: T): T => {
   return decorateObject(defaults, 'decorateWindowClass');
 };
 
-export const decorateSessionOptions = defaults => {
+export const decorateSessionOptions = <T>(defaults: T): T => {
   return decorateObject(defaults, 'decorateSessionOptions');
 };
 
-export const decorateSessionClass = Session => {
+export const decorateSessionClass = <T>(Session: T): T => {
   return decorateClass(Session, 'decorateSessionClass');
 };
 
diff --git a/app/session.js b/app/session.ts
similarity index 83%
rename from app/session.js
rename to app/session.ts
index 8397c8c8..7835795a 100644
--- a/app/session.js
+++ b/app/session.ts
@@ -2,15 +2,16 @@ import {EventEmitter} from 'events';
 import {StringDecoder} from 'string_decoder';
 import defaultShell from 'default-shell';
 import {getDecoratedEnv} from './plugins';
-import {productName, version} from './package';
+import {productName, version} from './package.json';
 import * as config from './config';
+import {IPty, IWindowsPtyForkOptions, spawn as npSpawn} from 'node-pty';
 
 const createNodePtyError = () =>
   new Error(
     '`node-pty` failed to load. Typically this means that it was built incorrectly. Please check the `readme.md` to more info.'
   );
 
-let spawn;
+let spawn: typeof npSpawn;
 try {
   spawn = require('node-pty').spawn;
 } catch (err) {
@@ -33,7 +34,11 @@ const BATCH_MAX_SIZE = 200 * 1024;
 // with the window ID which is then stripped on the renderer process and this
 // overhead is reduced with batching.
 class DataBatcher extends EventEmitter {
-  constructor(uid) {
+  uid: string;
+  decoder: StringDecoder;
+  data!: string;
+  timeout!: NodeJS.Timeout | null;
+  constructor(uid: string) {
     super();
     this.uid = uid;
     this.decoder = new StringDecoder('utf8');
@@ -46,7 +51,7 @@ class DataBatcher extends EventEmitter {
     this.timeout = null;
   }
 
-  write(chunk) {
+  write(chunk: Buffer) {
     if (this.data.length + chunk.length >= BATCH_MAX_SIZE) {
       // We've reached the max batch size. Flush it and start another one
       if (this.timeout) {
@@ -72,8 +77,20 @@ class DataBatcher extends EventEmitter {
   }
 }
 
+interface SessionOptions {
+  uid: string;
+  rows: number;
+  cols: number;
+  cwd: string;
+  shell: string;
+  shellArgs: string[];
+}
 export default class Session extends EventEmitter {
-  constructor(options) {
+  pty: IPty | null;
+  batcher: DataBatcher | null;
+  shell: string | null;
+  ended: boolean;
+  constructor(options: SessionOptions) {
     super();
     this.pty = null;
     this.batcher = null;
@@ -82,8 +99,9 @@ export default class Session extends EventEmitter {
     this.init(options);
   }
 
-  init({uid, rows, cols: columns, cwd, shell, shellArgs}) {
-    const osLocale = require('os-locale');
+  init({uid, rows, cols: columns, cwd, shell, shellArgs}: SessionOptions) {
+    // eslint-disable-next-line @typescript-eslint/no-var-requires
+    const osLocale = require('os-locale') as typeof import('os-locale');
     const baseEnv = Object.assign(
       {},
       process.env,
@@ -106,7 +124,7 @@ export default class Session extends EventEmitter {
 
     const defaultShellArgs = ['--login'];
 
-    const options = {
+    const options: IWindowsPtyForkOptions = {
       cols: columns,
       rows,
       cwd,
@@ -133,7 +151,7 @@ export default class Session extends EventEmitter {
       if (this.ended) {
         return;
       }
-      this.batcher.write(chunk);
+      this.batcher?.write(chunk as any);
     });
 
     this.batcher.on('flush', data => {
@@ -154,7 +172,7 @@ export default class Session extends EventEmitter {
     this.destroy();
   }
 
-  write(data) {
+  write(data: string) {
     if (this.pty) {
       this.pty.write(data);
     } else {
@@ -163,7 +181,7 @@ export default class Session extends EventEmitter {
     }
   }
 
-  resize({cols, rows}) {
+  resize({cols, rows}: {cols: number; rows: number}) {
     if (this.pty) {
       try {
         this.pty.resize(cols, rows);
diff --git a/app/system-context-menu.js b/app/system-context-menu.ts
similarity index 92%
rename from app/system-context-menu.js
rename to app/system-context-menu.ts
index 06b1b6e7..96419769 100644
--- a/app/system-context-menu.js
+++ b/app/system-context-menu.ts
@@ -8,7 +8,7 @@ const regParts = [
   {name: 'Icon', value: `${appPath}`}
 ];
 
-function addValues(hyperKey, commandKey, callback) {
+function addValues(hyperKey: Registry.Registry, commandKey: Registry.Registry, callback: Function) {
   hyperKey.set(regParts[1].name, Registry.REG_SZ, regParts[1].value, error => {
     if (error) {
       //eslint-disable-next-line no-console
@@ -30,7 +30,7 @@ function addValues(hyperKey, commandKey, callback) {
   });
 }
 
-export const add = callback => {
+export const add = (callback: Function) => {
   const hyperKey = new Registry({hive: 'HKCU', key: regKey});
   const commandKey = new Registry({
     hive: 'HKCU',
@@ -78,7 +78,7 @@ export const add = callback => {
   });
 };
 
-export const remove = callback => {
+export const remove = (callback: Function) => {
   new Registry({hive: 'HKCU', key: regKey}).destroy(err => {
     if (err) {
       //eslint-disable-next-line no-console
diff --git a/app/ui/window.ts b/app/ui/window.ts
index 99d45011..7bac1a0e 100644
--- a/app/ui/window.ts
+++ b/app/ui/window.ts
@@ -111,7 +111,7 @@ export function newWindow(
     }
   });
 
-  function createSession(extraOptions = {}) {
+  function createSession(extraOptions: any = {}) {
     const uid = uuid.v4();
 
     // remove the rows and cols, the wrong value of them will break layout when init create
diff --git a/package.json b/package.json
index 15cb4158..1bc376a3 100644
--- a/package.json
+++ b/package.json
@@ -67,6 +67,7 @@
     "@babel/preset-react": "7.7.4",
     "@babel/preset-typescript": "7.7.7",
     "@types/args": "3.0.0",
+    "@types/async-retry": "1.4.1",
     "@types/color": "3.0.0",
     "@types/columnify": "^1.5.0",
     "@types/electron-devtools-installer": "2.2.0",
diff --git a/yarn.lock b/yarn.lock
index f1adbad0..42963b04 100644
--- a/yarn.lock
+++ b/yarn.lock
@@ -596,6 +596,13 @@
   resolved "https://registry.yarnpkg.com/@types/args/-/args-3.0.0.tgz#2fd21cfbdaf5e1ed110bd239de42a82330d6ecf6"
   integrity sha512-2A817ZtVj1/nD44MV0/U/R6xe3GM2n1WDdni4ioCuLjay6dE0bLJd5RafHC/ddqwXL1xa2RQUdJhsGZKyr3vpA==
 
+"@types/async-retry@1.4.1":
+  version "1.4.1"
+  resolved "https://registry.yarnpkg.com/@types/async-retry/-/async-retry-1.4.1.tgz#3b136a707b7a850f4947a727eb0f7b473b601992"
+  integrity sha512-hDI5Ttk9SUmDLcD/Yl2VuWQRGYZjJ7aaJFeRlomUOz/iTKSE7yA55SwY87QwjiZgwhMlVAKoT1rl08UyQoheag==
+  dependencies:
+    "@types/retry" "*"
+
 "@types/cacheable-request@^6.0.1":
   version "6.0.1"
   resolved "https://registry.yarnpkg.com/@types/cacheable-request/-/cacheable-request-6.0.1.tgz#5d22f3dded1fd3a84c0bbeb5039a7419c2c91976"
@@ -773,6 +780,11 @@
   dependencies:
     "@types/node" "*"
 
+"@types/retry@*":
+  version "0.12.0"
+  resolved "https://registry.yarnpkg.com/@types/retry/-/retry-0.12.0.tgz#2b35eccfcee7d38cd72ad99232fbd58bffb3c84d"
+  integrity sha512-wWKOClTTiizcZhXnPY4wikVAwmdYHp8q6DmC+EJUzAMsycb7HB32Kh9RN4+0gExjmPmZSAQjgURXIGATPegAvA==
+
 "@types/seamless-immutable@7.1.11":
   version "7.1.11"
   resolved "https://registry.yarnpkg.com/@types/seamless-immutable/-/seamless-immutable-7.1.11.tgz#89250c3e2587a44c2a051f5798e6f29f0e91bbc9"