diff --git a/src/shared/blacklists.ts b/src/shared/blacklists.ts
index 61720c3..61ee4de 100644
--- a/src/shared/blacklists.ts
+++ b/src/shared/blacklists.ts
@@ -1,6 +1,6 @@
-import * as re from 'shared/utils/re';
+import * as re from './utils/re';
 
-const includes = (blacklist, url) => {
+const includes = (blacklist: string[], url: string): boolean => {
   let u = new URL(url);
   return blacklist.some((item) => {
     if (!item.includes('/')) {
diff --git a/src/shared/messages.ts b/src/shared/messages.ts
index ddf3368..2bc12d8 100644
--- a/src/shared/messages.ts
+++ b/src/shared/messages.ts
@@ -1,5 +1,8 @@
-const onWebMessage = (listener) => {
-  window.addEventListener('message', (event) => {
+type WebMessageSender = Window | MessagePort | ServiceWorker | null;
+type WebMessageListener = (msg: any, sender: WebMessageSender | null) => void;
+
+const onWebMessage = (listener: WebMessageListener) => {
+  window.addEventListener('message', (event: MessageEvent) => {
     let sender = event.source;
     let message = null;
     try {
@@ -12,11 +15,15 @@ const onWebMessage = (listener) => {
   });
 };
 
-const onBackgroundMessage = (listener) => {
+const onBackgroundMessage = (
+  listener: (msg: any, sender: browser.runtime.MessageSender,
+) => void) => {
   browser.runtime.onMessage.addListener(listener);
 };
 
-const onMessage = (listener) => {
+const onMessage = (
+  listener: (msg: any, sender: WebMessageSender | browser.runtime.MessageSender,
+) => void) => {
   onWebMessage(listener);
   onBackgroundMessage(listener);
 };
diff --git a/src/shared/operations.ts b/src/shared/operations.ts
index 8674f4d..d59723e 100644
--- a/src/shared/operations.ts
+++ b/src/shared/operations.ts
@@ -1,4 +1,4 @@
-export default {
+const operations: { [key: string]: string } = {
   // Hide console, or cancel some user actions
   CANCEL: 'cancel',
 
@@ -76,3 +76,5 @@ export default {
   MARK_SET_PREFIX: 'mark.set.prefix',
   MARK_JUMP_PREFIX: 'mark.jump.prefix',
 };
+
+export default operations;
diff --git a/src/shared/settings/properties.ts b/src/shared/settings/properties.ts
index f8e61a0..7d037df 100644
--- a/src/shared/settings/properties.ts
+++ b/src/shared/settings/properties.ts
@@ -2,20 +2,20 @@
 //    mystr: 'string',
 //    mynum: 'number',
 //    mybool: 'boolean',
-const types = {
+const types: { [key: string]: string } = {
   hintchars: 'string',
   smoothscroll: 'boolean',
   complete: 'string',
 };
 
 // describe default values of a property
-const defaults = {
+const defaults: { [key: string]: string | number | boolean } = {
   hintchars: 'abcdefghijklmnopqrstuvwxyz',
   smoothscroll: false,
   complete: 'sbh',
 };
 
-const docs = {
+const docs: { [key: string]: string } = {
   hintchars: 'hint characters on follow mode',
   smoothscroll: 'smooth scroll',
   complete: 'which are completed at the open page',
diff --git a/src/shared/settings/storage.ts b/src/shared/settings/storage.ts
index 5dce3b0..90a3a66 100644
--- a/src/shared/settings/storage.ts
+++ b/src/shared/settings/storage.ts
@@ -1,12 +1,12 @@
 import DefaultSettings from './default';
 import * as settingsValues from './values';
 
-const loadRaw = async() => {
+const loadRaw = async(): Promise<any> => {
   let { settings } = await browser.storage.local.get('settings');
   if (!settings) {
     return DefaultSettings;
   }
-  return { ...DefaultSettings, ...settings };
+  return { ...DefaultSettings, ...settings as object };
 };
 
 const loadValue = async() => {
@@ -23,7 +23,7 @@ const loadValue = async() => {
   return { ...settingsValues.valueFromJson(DefaultSettings.json), ...value };
 };
 
-const save = (settings) => {
+const save = (settings: any): Promise<any> => {
   return browser.storage.local.set({
     settings,
   });
diff --git a/src/shared/settings/validator.ts b/src/shared/settings/validator.ts
index a800a52..0483931 100644
--- a/src/shared/settings/validator.ts
+++ b/src/shared/settings/validator.ts
@@ -1,4 +1,4 @@
-import operations from 'shared/operations';
+import operations from '../operations';
 import * as properties from './properties';
 
 const VALID_TOP_KEYS = ['keymaps', 'search', 'blacklist', 'properties'];
@@ -6,7 +6,7 @@ const VALID_OPERATION_VALUES = Object.keys(operations).map((key) => {
   return operations[key];
 });
 
-const validateInvalidTopKeys = (settings) => {
+const validateInvalidTopKeys = (settings: any): void => {
   let invalidKey = Object.keys(settings).find((key) => {
     return !VALID_TOP_KEYS.includes(key);
   });
@@ -15,7 +15,7 @@ const validateInvalidTopKeys = (settings) => {
   }
 };
 
-const validateKeymaps = (keymaps) => {
+const validateKeymaps = (keymaps: any): void => {
   for (let key of Object.keys(keymaps)) {
     let value = keymaps[key];
     if (!VALID_OPERATION_VALUES.includes(value.type)) {
@@ -24,7 +24,7 @@ const validateKeymaps = (keymaps) => {
   }
 };
 
-const validateSearch = (search) => {
+const validateSearch = (search: any): void => {
   let engines = search.engines;
   for (let key of Object.keys(engines)) {
     if ((/\s/).test(key)) {
@@ -49,7 +49,7 @@ const validateSearch = (search) => {
   }
 };
 
-const validateProperties = (props) => {
+const validateProperties = (props: any): void => {
   for (let name of Object.keys(props)) {
     if (!properties.types[name]) {
       throw new Error(`Unknown property name: "${name}"`);
@@ -60,7 +60,7 @@ const validateProperties = (props) => {
   }
 };
 
-const validate = (settings) => {
+const validate = (settings: any): void => {
   validateInvalidTopKeys(settings);
   if (settings.keymaps) {
     validateKeymaps(settings.keymaps);
diff --git a/src/shared/settings/values.ts b/src/shared/settings/values.ts
index 9828af6..cb6a668 100644
--- a/src/shared/settings/values.ts
+++ b/src/shared/settings/values.ts
@@ -1,6 +1,6 @@
 import * as properties from './properties';
 
-const operationFromFormName = (name) => {
+const operationFromFormName = (name: string): any => {
   let [type, argStr] = name.split('?');
   let args = {};
   if (argStr) {
@@ -9,7 +9,7 @@ const operationFromFormName = (name) => {
   return { type, ...args };
 };
 
-const operationToFormName = (op) => {
+const operationToFormName = (op: any): string => {
   let type = op.type;
   let args = { ...op };
   delete args.type;
@@ -20,12 +20,12 @@ const operationToFormName = (op) => {
   return op.type + '?' + JSON.stringify(args);
 };
 
-const valueFromJson = (json) => {
+const valueFromJson = (json: string): object => {
   return JSON.parse(json);
 };
 
-const valueFromForm = (form) => {
-  let keymaps = undefined;
+const valueFromForm = (form: any): object => {
+  let keymaps: any = undefined;
   if (form.keymaps) {
     keymaps = {};
     for (let name of Object.keys(form.keymaps)) {
@@ -34,7 +34,7 @@ const valueFromForm = (form) => {
     }
   }
 
-  let search = undefined;
+  let search: any = undefined;
   if (form.search) {
     search = { default: form.search.default };
 
@@ -54,12 +54,12 @@ const valueFromForm = (form) => {
   };
 };
 
-const jsonFromValue = (value) => {
+const jsonFromValue = (value: any): string => {
   return JSON.stringify(value, undefined, 2);
 };
 
-const formFromValue = (value, allowedOps) => {
-  let keymaps = undefined;
+const formFromValue = (value: any, allowedOps: any[]): any => {
+  let keymaps: any = undefined;
 
   if (value.keymaps) {
     let allowedSet = new Set(allowedOps);
@@ -73,7 +73,7 @@ const formFromValue = (value, allowedOps) => {
     }
   }
 
-  let search = undefined;
+  let search: any = undefined;
   if (value.search) {
     search = { default: value.search.default };
     if (value.search.engines) {
@@ -93,11 +93,11 @@ const formFromValue = (value, allowedOps) => {
   };
 };
 
-const jsonFromForm = (form) => {
+const jsonFromForm = (form: any): string => {
   return jsonFromValue(valueFromForm(form));
 };
 
-const formFromJson = (json, allowedOps) => {
+const formFromJson = (json: string, allowedOps: any[]): any => {
   let value = valueFromJson(json);
   return formFromValue(value, allowedOps);
 };
diff --git a/src/shared/urls.ts b/src/shared/urls.ts
index 94b1220..18349c8 100644
--- a/src/shared/urls.ts
+++ b/src/shared/urls.ts
@@ -1,11 +1,11 @@
-const trimStart = (str) => {
+const trimStart = (str: string): string => {
   // NOTE String.trimStart is available on Firefox 61
   return str.replace(/^\s+/, '');
 };
 
 const SUPPORTED_PROTOCOLS = ['http:', 'https:', 'ftp:', 'mailto:', 'about:'];
 
-const searchUrl = (keywords, searchSettings) => {
+const searchUrl = (keywords: string, searchSettings: any): string => {
   try {
     let u = new URL(keywords);
     if (SUPPORTED_PROTOCOLS.includes(u.protocol.toLowerCase())) {
@@ -28,7 +28,7 @@ const searchUrl = (keywords, searchSettings) => {
   return template.replace('{}', encodeURIComponent(query));
 };
 
-const normalizeUrl = (url) => {
+const normalizeUrl = (url: string): string => {
   try {
     let u = new URL(url);
     if (SUPPORTED_PROTOCOLS.includes(u.protocol.toLowerCase())) {
diff --git a/src/shared/utils/dom.ts b/src/shared/utils/dom.ts
index 974d534..c1f2190 100644
--- a/src/shared/utils/dom.ts
+++ b/src/shared/utils/dom.ts
@@ -1,16 +1,24 @@
-const isContentEditable = (element) => {
-  return element.hasAttribute('contenteditable') && (
-    element.getAttribute('contenteditable').toLowerCase() === 'true' ||
-    element.getAttribute('contenteditable').toLowerCase() === ''
-  );
+const isContentEditable = (element: Element): boolean => {
+  let value = element.getAttribute('contenteditable');
+  if (value === null) {
+    return false;
+  }
+  return value.toLowerCase() === 'true' || value.toLowerCase() === '';
 };
 
-const rectangleCoordsRect = (coords) => {
+interface Rect {
+  left: number;
+  top: number;
+  right: number;
+  bottom: number;
+}
+
+const rectangleCoordsRect = (coords: string): Rect => {
   let [left, top, right, bottom] = coords.split(',').map(n => Number(n));
   return { left, top, right, bottom };
 };
 
-const circleCoordsRect = (coords) => {
+const circleCoordsRect = (coords: string): Rect => {
   let [x, y, r] = coords.split(',').map(n => Number(n));
   return {
     left: x - r,
@@ -20,7 +28,7 @@ const circleCoordsRect = (coords) => {
   };
 };
 
-const polygonCoordsRect = (coords) => {
+const polygonCoordsRect = (coords: string): Rect => {
   let params = coords.split(',');
   let minx = Number(params[0]),
     maxx = Number(params[0]),
@@ -46,18 +54,24 @@ const polygonCoordsRect = (coords) => {
   return { left: minx, top: miny, right: maxx, bottom: maxy };
 };
 
-const viewportRect = (e) => {
+const viewportRect = (e: Element): Rect => {
   if (e.tagName !== 'AREA') {
     return e.getBoundingClientRect();
   }
 
-  let mapElement = e.parentNode;
-  let imgElement = document.querySelector(`img[usemap="#${mapElement.name}"]`);
+  let mapElement = e.parentNode as HTMLMapElement;
+  let imgElement = document.querySelector(
+    `img[usemap="#${mapElement.name}"]`
+  ) as HTMLImageElement;
   let {
     left: mapLeft,
     top: mapTop
   } = imgElement.getBoundingClientRect();
   let coords = e.getAttribute('coords');
+  if (!coords) {
+    return e.getBoundingClientRect();
+  }
+
   let rect = { left: 0, top: 0, right: 0, bottom: 0 };
   switch (e.getAttribute('shape')) {
   case 'rect':
@@ -81,7 +95,7 @@ const viewportRect = (e) => {
   };
 };
 
-const isVisible = (element) => {
+const isVisible = (element: Element): boolean => {
   let rect = element.getBoundingClientRect();
   let style = window.getComputedStyle(element);
 
@@ -94,7 +108,8 @@ const isVisible = (element) => {
   if (window.innerWidth < rect.left && window.innerHeight < rect.top) {
     return false;
   }
-  if (element.nodeName === 'INPUT' && element.type.toLowerCase() === 'hidden') {
+  if (element instanceof HTMLInputElement &&
+    element.type.toLowerCase() === 'hidden') {
     return false;
   }
 
diff --git a/src/shared/utils/keys.ts b/src/shared/utils/keys.ts
index f024069..d9abef7 100644
--- a/src/shared/utils/keys.ts
+++ b/src/shared/utils/keys.ts
@@ -1,4 +1,12 @@
-const modifiedKeyName = (name) => {
+interface Key {
+    key: string;
+    shiftKey: boolean | undefined;
+    ctrlKey: boolean | undefined;
+    altKey: boolean | undefined;
+    metaKey: boolean | undefined;
+}
+
+const modifiedKeyName = (name: string): string => {
   if (name === ' ') {
     return 'Space';
   }
@@ -10,7 +18,7 @@ const modifiedKeyName = (name) => {
   return name;
 };
 
-const fromKeyboardEvent = (e) => {
+const fromKeyboardEvent = (e: KeyboardEvent): Key => {
   let key = modifiedKeyName(e.key);
   let shift = e.shiftKey;
   if (key.length === 1 && key.toUpperCase() === key.toLowerCase()) {
@@ -28,7 +36,7 @@ const fromKeyboardEvent = (e) => {
   };
 };
 
-const fromMapKey = (key) => {
+const fromMapKey = (key: string): Key => {
   if (key.startsWith('<') && key.endsWith('>')) {
     let inner = key.slice(1, -1);
     let shift = inner.includes('S-');
@@ -55,8 +63,10 @@ const fromMapKey = (key) => {
   };
 };
 
-const fromMapKeys = (keys) => {
-  const fromMapKeysRecursive = (remainings, mappedKeys) => {
+const fromMapKeys = (keys: string): Key[] => {
+  const fromMapKeysRecursive = (
+    remainings: string, mappedKeys: Key[],
+  ): Key[] => {
     if (remainings.length === 0) {
       return mappedKeys;
     }
@@ -78,7 +88,7 @@ const fromMapKeys = (keys) => {
   return fromMapKeysRecursive(keys, []);
 };
 
-const equals = (e1, e2) => {
+const equals = (e1: Key, e2: Key): boolean => {
   return e1.key === e2.key &&
     e1.ctrlKey === e2.ctrlKey &&
     e1.metaKey === e2.metaKey &&
diff --git a/src/shared/utils/re.ts b/src/shared/utils/re.ts
index 7db9091..34f4fa6 100644
--- a/src/shared/utils/re.ts
+++ b/src/shared/utils/re.ts
@@ -1,4 +1,4 @@
-const fromWildcard = (pattern) => {
+const fromWildcard = (pattern: string): RegExp => {
   let regexStr = '^' + pattern.replace(/\*/g, '.*') + '$';
   return new RegExp(regexStr);
 };