diff --git a/src/components/Add.jsx b/src/components/Add.tsx
similarity index 82%
rename from src/components/Add.jsx
rename to src/components/Add.tsx
index e0062e5..b1cf2d9 100644
--- a/src/components/Add.jsx
+++ b/src/components/Add.tsx
@@ -1,12 +1,17 @@
 import React from "react";
 
-import useForm from "../hooks/useForm";
-import useFirebase from "../hooks/useFirebase";
+import useForm, { InputInterface, ActionInterface } from "../hooks/useForm";
+import useFirebase, { WordInterface } from "../hooks/useFirebase";
+
+interface PropsInterface {
+  onAdd: Function;
+}
 
 const INITIAL_STATE = [
   {
     name: "type",
-    type: "select",
+    type: "select" as const,
+    value: "",
     placeholder: "Type",
     required: true,
     options: [
@@ -19,7 +24,7 @@ const INITIAL_STATE = [
   },
   {
     name: "article",
-    type: "select",
+    type: "select" as const,
     value: "",
     required: true,
     options: [
@@ -33,26 +38,26 @@ const INITIAL_STATE = [
   {
     name: "word",
     placeholder: "Word",
-    type: "text",
+    type: "text" as const,
     value: "",
     required: true
   },
   {
     name: "meaning",
     placeholder: "Meaning",
-    type: "text",
+    type: "text" as const,
     value: "",
     required: true
   },
   {
     name: "note",
     placeholder: "Note",
-    type: "text",
+    type: "text" as const,
     value: ""
   }
 ];
 
-function reducer(state, action) {
+function reducer(state: InputInterface[], action: ActionInterface) {
   const { type, name, value } = action;
 
   if (type === "edit" && name === "type") {
@@ -77,11 +82,11 @@ function reducer(state, action) {
   return state;
 }
 
-function validator(inputs) {
+function validator(inputs: InputInterface[]) {
   const inputMap = inputs.reduce((map, input) => {
     map[input.name] = input;
     return map;
-  }, {});
+  }, {} as { [key: string]: InputInterface });
 
   const requiredInputs = !inputs.some(input => {
     if (input.required && !input.value) {
@@ -103,7 +108,7 @@ function validator(inputs) {
   }
 }
 
-function Add({ onAdd }) {
+function Add({ onAdd }: PropsInterface) {
   const { state, isValid, change, reset } = useForm(INITIAL_STATE, {
     reducer,
     validator
@@ -116,7 +121,7 @@ function Add({ onAdd }) {
         ...prev,
         [property.name]: property.value
       };
-    }, {});
+    }, {} as WordInterface);
     addWordToFirebase(word).then(() => {
       reset();
       onAdd();
@@ -135,7 +140,7 @@ function Add({ onAdd }) {
               onChange={change}
               disabled={input.disabled}
             >
-              {input.options.map(option => (
+              {input.options?.map(option => (
                 <option key={option.value} value={option.value}>
                   {option.label}
                 </option>
diff --git a/src/components/App.jsx b/src/components/App.tsx
similarity index 69%
rename from src/components/App.jsx
rename to src/components/App.tsx
index 0206003..1ab025e 100644
--- a/src/components/App.jsx
+++ b/src/components/App.tsx
@@ -1,19 +1,23 @@
 import React, { useState, useEffect } from "react";
 import "./App.css";
 
-import useFirebase from "../hooks/useFirebase";
+import useFirebase, { WordInterface } from "../hooks/useFirebase";
 
 import Login from "./Login";
 import Add from "./Add";
 import View from "./View";
 
+interface Global {
+  logout?: Function;
+}
+
 function App() {
-  const [words, setWords] = useState([]);
+  const [words, setWords] = useState<WordInterface[]>([]);
   const { user, getAllWords, logout } = useFirebase();
-  window.logout = logout;
+  (window as Global).logout = logout;
 
   const getWords = () => {
-    getAllWords().then(setWords);
+    getAllWords().then(words => words && setWords(words));
   };
 
   useEffect(getWords, [getAllWords]);
diff --git a/src/components/Login.jsx b/src/components/Login.tsx
similarity index 89%
rename from src/components/Login.jsx
rename to src/components/Login.tsx
index 523d109..b8d3709 100644
--- a/src/components/Login.jsx
+++ b/src/components/Login.tsx
@@ -6,14 +6,14 @@ import useFirebase from "../hooks/useFirebase";
 const INITIAL_STATE = [
   {
     placeholder: "Email",
-    type: "email",
+    type: "email" as const,
     name: "email",
     value: "blessanm86@gmail.com",
     required: true
   },
   {
     placeholder: "Password",
-    type: "password",
+    type: "password" as const,
     name: "password",
     value: "",
     required: true
@@ -30,7 +30,7 @@ function Login() {
         ...prev,
         [property.name]: property.value
       };
-    }, {});
+    }, {} as { email: string; password: string });
     loginToFirebase(email, password);
     reset();
   };
diff --git a/src/components/View.jsx b/src/components/View.tsx
similarity index 77%
rename from src/components/View.jsx
rename to src/components/View.tsx
index 086e044..a1646cb 100644
--- a/src/components/View.jsx
+++ b/src/components/View.tsx
@@ -1,6 +1,11 @@
 import React from "react";
+import { WordInterface } from "../hooks/useFirebase";
 
-function View({ words = [] }) {
+interface PropsInterface {
+  words: WordInterface[];
+}
+
+function View({ words = [] }: PropsInterface) {
   return (
     <section className="wb-view">
       {words.map(({ word, article, meaning, note, type }, index) => (
diff --git a/src/hooks/useFirebase.js b/src/hooks/useFirebase.ts
similarity index 62%
rename from src/hooks/useFirebase.js
rename to src/hooks/useFirebase.ts
index c56f4ed..974f762 100644
--- a/src/hooks/useFirebase.js
+++ b/src/hooks/useFirebase.ts
@@ -3,6 +3,15 @@ import * as firebase from "firebase/app";
 import "firebase/auth";
 import "firebase/firestore";
 
+export interface WordInterface {
+  article: string;
+  meaning: string;
+  note: string;
+  timestamp: firebase.firestore.Timestamp;
+  type: string;
+  word: string;
+}
+
 const firebaseConfig = {
   apiKey: "AIzaSyAWznMXfEF-FMt9OUT10Twzxr382zfs3MU",
   authDomain: "mein-woerterbuch.firebaseapp.com",
@@ -14,7 +23,7 @@ const firebaseConfig = {
   measurementId: "G-06SEN5MFN2"
 };
 
-function loginToFirebase(email, password) {
+function loginToFirebase(email: string, password: string): void {
   firebase
     .auth()
     .signInWithEmailAndPassword(email, password)
@@ -34,7 +43,7 @@ function logout() {
   firebase.auth().signOut();
 }
 
-function addWordToFirebase(word) {
+function addWordToFirebase(word: WordInterface): Promise<string | Error> {
   word.timestamp = firebase.firestore.Timestamp.now();
 
   return firebase
@@ -42,39 +51,45 @@ function addWordToFirebase(word) {
     .collection("woerte")
     .add(word)
     .then(function(docRef) {
-      console.log("Document written with ID: ", docRef.id);
+      const result = `Document written with ID: ${docRef.id}`;
+      console.log(result);
+      return result;
     })
     .catch(function(error) {
-      console.error("Error adding document: ", error);
+      const result = `Error adding document: ${error}`;
+      console.error(result);
+      return result;
     });
 }
 
-function getAllWords() {
+function getAllWords(): Promise<WordInterface[] | void> {
   return firebase
     .firestore()
     .collection("woerte")
     .orderBy("timestamp", "desc")
     .get()
     .then(snapshot => {
-      const words = [];
-      snapshot.forEach(doc => words.push(doc.data()));
+      const words: WordInterface[] = [];
+      snapshot.forEach(doc => words.push(doc.data() as WordInterface));
       return words;
     })
-    .catch(err => console.log(err));
+    .catch(error => {
+      console.log(error);
+    });
 }
 
-let firbaseAuthStateListener;
-
 function useFirebase() {
-  const [user, setUser] = useState(null);
+  const [user, setUser] = useState<firebase.User | null>(null);
 
   !firebase.apps.length && firebase.initializeApp(firebaseConfig);
 
-  useEffect(() => {
-    firbaseAuthStateListener = firebase.auth().onAuthStateChanged(setUser);
-
-    return () => firbaseAuthStateListener();
-  }, []);
+  useEffect(
+    () =>
+      firebase.auth().onAuthStateChanged(user => {
+        user && setUser(user);
+      }),
+    []
+  );
 
   return {
     user,
diff --git a/src/hooks/useForm.ts b/src/hooks/useForm.ts
index 5ac90fe..2161c9b 100644
--- a/src/hooks/useForm.ts
+++ b/src/hooks/useForm.ts
@@ -1,8 +1,8 @@
-import { useReducer, ChangeEvent } from "react";
+import { useReducer, ChangeEventHandler, ChangeEvent } from "react";
 
-interface Input {
+export interface InputInterface {
   name: string;
-  type: string;
+  type: "text" | "password" | "email" | "select";
   placeholder?: string;
   required?: boolean;
   disabled?: boolean;
@@ -10,26 +10,31 @@ interface Input {
   value: string;
 }
 
-interface Options {
+interface OptionsInterface {
   reducer?: Function;
   validator?: Function;
 }
 
-interface State {
-  state: Array<Input>;
+interface FormInterface {
+  state: InputInterface[];
   isValid: boolean;
-  change: Function;
+  change: ChangeEventHandler;
   reset: Function;
 }
 
-interface Action {
+export interface ActionInterface {
   type: string;
   name?: string;
   value?: string;
 }
 
-function useForm(inputs: Array<Input>, options: Options = {}): State {
-  function change(evt: ChangeEvent<HTMLInputElement | HTMLSelectElement>) {
+function useForm(
+  inputs: InputInterface[],
+  options: OptionsInterface = {}
+): FormInterface {
+  function change(
+    evt: ChangeEvent<HTMLInputElement | HTMLSelectElement>
+  ): void {
     const {
       target: { name, value }
     } = evt;
@@ -40,7 +45,7 @@ function useForm(inputs: Array<Input>, options: Options = {}): State {
     dispatch({ type: "reset" });
   }
 
-  function validator(inputs: Array<Input>) {
+  function validator(inputs: InputInterface[]) {
     return !inputs.some(input => {
       if (input.required && !input.value) {
         return true;
@@ -50,7 +55,10 @@ function useForm(inputs: Array<Input>, options: Options = {}): State {
     });
   }
 
-  function reducer(state: State, action: Action): State {
+  function reducer(
+    state: FormInterface,
+    action: ActionInterface
+  ): FormInterface {
     const { state: inputs } = state;
     const { type, name, value } = action;