diff --git a/javascript-practice/src/js/constants/constant.js b/javascript-practice/src/js/constants/constant.js
index 08aa875..397a4ef 100644
--- a/javascript-practice/src/js/constants/constant.js
+++ b/javascript-practice/src/js/constants/constant.js
@@ -3,10 +3,7 @@ export const MESSAGE = {
   PASSWORD_NOT_STRONG:
     'Password must at least one uppercase, one lowercase letter, one number and one special character!',
   ERROR_MESSAGE_DEFAULT: 'Something went wrong!',
+  TIME_OUT_ERROR: 'Connection time out! Please try again!',
 };
-export const TIME_OUT_ERROR = {
-  status: 408,
-  message: 'Connection time out! Please try again!',
-};
-export const TYPE_FORM = { success: 'success', error: 'error' };
+export const TYPE_POPUP = { success: 'success', error: 'error' };
 export const MARK_ICON = { success: 'check', error: 'error' };
diff --git a/javascript-practice/src/js/controller.js b/javascript-practice/src/js/controller.js
index a420803..e69de29 100644
--- a/javascript-practice/src/js/controller.js
+++ b/javascript-practice/src/js/controller.js
@@ -1 +0,0 @@
-console.log('Hello World!');
diff --git a/javascript-practice/src/js/helpers/helpers.js b/javascript-practice/src/js/helpers/helpers.js
index ab8e3a7..c6adaf1 100644
--- a/javascript-practice/src/js/helpers/helpers.js
+++ b/javascript-practice/src/js/helpers/helpers.js
@@ -1,29 +1,37 @@
-import {
-  TIME_OUT_SEC,
-  TIME_OUT_ERROR,
-  REGEX_PASSWORD,
-} from '../constants/constant';
+import { MESSAGE } from '../constants/constant';
+import { REGEX_PASSWORD, TIME_OUT_SEC } from '../constants/config';
 import FirebaseService from '../services/firebaseService';
 
+/**
+ * Validate password
+ * @param {string} password Password input
+ * @returns {boolean} Return true if validate password success, otherwise return false
+ */
 export const validatePassword = (password) => {
   return REGEX_PASSWORD.test(password);
 };
 
+/**
+ * A waiting function with s second
+ * @param {number} s The time will be waiting
+ * @returns {Promise} A Promise will be only reject after s second
+ */
 export const timeout = (s) => {
-  return new Promise((reject) => {
+  return new Promise((_, reject) => {
     setTimeout(() => {
-      reject(TIME_OUT_ERROR);
+      FirebaseService.disconnect();
+      reject(MESSAGE.TIME_OUT_ERROR);
     }, s * 1000);
   });
 };
 
+/**
+ * A function waiting the action need to be perform and throw error after s second.
+ * @param {Function} action The action need to be perform.
+ * @returns { Object || Error } Return the any object from Firebase or Error
+ */
 export const timeOutConnect = async (action) => {
   const result = await Promise.race([action, timeout(TIME_OUT_SEC)]);
 
-  if (result && result.status === TIME_OUT_ERROR.status) {
-    FirebaseService.disconnect();
-    throw new Error(`${result.message}`);
-  }
-
   return result;
 };
diff --git a/javascript-practice/src/js/services/firebaseService.js b/javascript-practice/src/js/services/firebaseService.js
index 8e8ebef..700e5ad 100644
--- a/javascript-practice/src/js/services/firebaseService.js
+++ b/javascript-practice/src/js/services/firebaseService.js
@@ -12,24 +12,43 @@ import { DATABASE_URL } from '../constants/config';
 class FirebaseService {
   constructor() {
     const firebaseConfig = {
-      DATABASE_URL,
+      databaseURL: DATABASE_URL,
     };
     this.app = initializeApp(firebaseConfig);
     this.db = getDatabase(this.app);
   }
 
+  /**
+   * Save data in database
+   * @param {Object} data The object need to save into database
+   * @param {string} path The path of database need to be save
+   * @returns {Promise} Return the relsoves when write to database completed
+   */
   save(data, path) {
     return set(ref(this.db, path), data);
   }
 
+  /**
+   * Disconnect to database
+   */
   disconnect() {
     goOffline(this.db);
   }
 
+  /**
+   * Reconnect to database
+   */
   reconnect() {
     goOnline(this.db);
   }
 
+  /**
+   * Find the key of value by property in database
+   * @param {string} path The path of database to be found
+   * @param {string} property The property of the value need to be found
+   * @param {value} value The value to compare in database
+   * @returns {Promise} Return the relsoves when find completed
+   */
   findKeyByPropery(path, property, value) {
     return new Promise((resolve) => {
       onValue(
diff --git a/javascript-practice/src/js/services/service.js b/javascript-practice/src/js/services/service.js
new file mode 100644
index 0000000..dd10508
--- /dev/null
+++ b/javascript-practice/src/js/services/service.js
@@ -0,0 +1,7 @@
+import UserService from './userService';
+
+export default class Service {
+  constructor() {
+    this.userService = new UserService();
+  }
+}
diff --git a/javascript-practice/src/js/services/userService.js b/javascript-practice/src/js/services/userService.js
new file mode 100644
index 0000000..65341ba
--- /dev/null
+++ b/javascript-practice/src/js/services/userService.js
@@ -0,0 +1,39 @@
+import { timeOutConnect } from '../helpers/helpers';
+import FirebaseService from './firebaseService';
+import User from '../models/userModel';
+
+export default class UserService {
+  constructor() {
+    this.path = 'users/';
+  }
+
+  /**
+   * Save user into database
+   * @param {Object} user The user object need to be saved into databae
+   */
+  async saveUser(user) {
+    FirebaseService.reconnect();
+    const saveUser = FirebaseService.save(
+      user,
+      this.path + User.createIdUser(),
+    );
+    await timeOutConnect(saveUser);
+  }
+
+  /**
+   * Check user exist in database by email
+   * @param {string} email Email need to be check
+   * @returns {boolean} Return true if email exist and otherwise is false
+   */
+  async checkExistUserByEmail(email) {
+    FirebaseService.reconnect();
+    const existUser = FirebaseService.findKeyByPropery(
+      this.path,
+      'email',
+      email,
+    );
+    const result = await timeOutConnect(existUser);
+
+    return result;
+  }
+}
diff --git a/javascript-practice/src/js/view/view.js b/javascript-practice/src/js/view/view.js
deleted file mode 100644
index 70b786d..0000000
--- a/javascript-practice/src/js/view/view.js
+++ /dev/null
@@ -1 +0,0 @@
-// TODO
diff --git a/javascript-practice/src/js/views/commonView.js b/javascript-practice/src/js/views/commonView.js
new file mode 100644
index 0000000..083f01f
--- /dev/null
+++ b/javascript-practice/src/js/views/commonView.js
@@ -0,0 +1,113 @@
+import { MARK_ICON, TYPE_POPUP } from '../constants/constant';
+
+export default class CommonView {
+  constructor() {
+    this.overlayMarkup = '<div class="overlay"></div>';
+
+    this.initPopup();
+    this.initElementPopup();
+    this.initLoader();
+    this.handleEventBtnPopupAndOverlay();
+  }
+
+  /**
+   * Implement popup in site
+   */
+  initPopup() {
+    this.rootElement = document.querySelector('body');
+
+    const markup = `
+      ${this.overlayMarkup}
+      <div class="modal-box">
+        <div class="mark"></div>
+        <h2 class="modal-box__title"></h2>
+        <p class="modal-box__message"></p>
+
+        <button class="modal-box__redirect-btn"></button>
+      </div>
+    `;
+
+    this.rootElement.insertAdjacentHTML('afterbegin', markup);
+  }
+
+  /**
+   * Assgign element in popup to property
+   */
+  initElementPopup() {
+    this.modalBox = document.querySelector('.modal-box');
+    this.popupIcon = document.querySelector('.mark');
+    this.popupBtn = document.querySelector('.modal-box__redirect-btn');
+    this.popupTitle = document.querySelector('.modal-box__title');
+    this.popupContent = document.querySelector('.modal-box__message');
+    this.overlay = document.querySelector('.overlay');
+  }
+
+  /**
+   * Show or hide loader screen
+   */
+  toogleLoaderSpinner() {
+    this.spinner.classList.toggle('hidden');
+  }
+
+  /**
+   * Show or hide popup
+   */
+  tooglePopupForm() {
+    this.overlay.classList.toggle('active');
+    this.modalBox.classList.toggle('active');
+  }
+
+  /**
+   * Add popup content
+   * @param {TYPE_POPUP} typePopup Type of the popup
+   * @param {string} title Title of popup
+   * @param {string} content Content of popup
+   * @param {string} btnContent Content of button
+   */
+  initPopupContent(typePopup, title, content, btnContent) {
+    // Remove old typePopup class if haved
+    this.modalBox.classList.forEach((classItem) =>
+      classItem === TYPE_POPUP.success || classItem === TYPE_POPUP.error
+        ? this.modalBox.classList.remove(classItem)
+        : '',
+    );
+
+    // Remove old icon popup if haved
+    this.popupIcon.classList.forEach((classItem) =>
+      classItem === MARK_ICON.success || classItem === MARK_ICON.error
+        ? this.popupIcon.classList.remove(classItem)
+        : '',
+    );
+
+    // Init content popup
+    this.modalBox.classList.add(
+      typePopup === TYPE_POPUP.success ? TYPE_POPUP.success : TYPE_POPUP.error,
+    );
+    this.popupIcon.classList.add(
+      typePopup === TYPE_POPUP.success ? MARK_ICON.success : MARK_ICON.error,
+    );
+    this.popupTitle.textContent = title;
+    this.popupContent.textContent = content;
+    this.popupBtn.textContent = btnContent;
+  }
+
+  /**
+   * Add event listener for popup and overlay
+   */
+  handleEventBtnPopupAndOverlay() {
+    this.popupBtn.addEventListener('click', this.tooglePopupForm.bind(this));
+    this.overlay.addEventListener('click', this.tooglePopupForm.bind(this));
+  }
+
+  /**
+   * Implement loader screen
+   */
+  initLoader() {
+    const markup = `<div class="loader hidden"></div>`;
+
+    this.rootElement.insertAdjacentHTML('afterbegin', markup);
+
+    // Init element
+    this.spinner = document.querySelector('.loader');
+  }
+}
diff --git a/javascript-practice/src/js/views/registerView.js b/javascript-practice/src/js/views/registerView.js
new file mode 100644
index 0000000..aa0576e
--- /dev/null
+++ b/javascript-practice/src/js/views/registerView.js
@@ -0,0 +1,163 @@
+import { validatePassword } from '../helpers/helpers';
+import * as CONSTANT from '../constants/constant';
+import CommonView from './commonView';
+import User from '../models/userModel';
+
+export default class RegisterView extends CommonView {
+  constructor() {
+    super();
+
+    this.parentElement = document.querySelector('.form');
+    this.inputField = document.querySelectorAll('.form__input');
+
+    this.messageDefault = CONSTANT.MESSAGE.ERROR_MESSAGE_DEFAULT;
+  }
+
+  /**
+   * Get data from user input
+   * @returns {Object || null} Return user object or null
+   */
+  getDataFromForm() {
+    const { registerForm } = document.forms;
+    const formData = new FormData(registerForm);
+    const email = formData.get('email');
+    const password = formData.get('password');
+    const passwordConfirm = formData.get('password_confirm');
+
+    const account = { email, password, passwordConfirm };
+
+    if (this.validateForm(account)) {
+      const user = new User(account);
+      return user;
+    }
+    return null;
+  }
+
+  /**
+   * Validate user input data
+   * @param {Object} account The account object with email, password, passwordConfirm field
+   * @returns {boolean} Return true if validate success and return false if validate not success
+   */
+  validateForm(account) {
+    if (account.password === account.passwordConfirm) {
+      if (validatePassword(account.passwordConfirm)) {
+        return true;
+      }
+      this.showError(CONSTANT.MESSAGE.PASSWORD_NOT_STRONG);
+      return false;
+    }
+    this.showError(CONSTANT.MESSAGE.PASSWORD_NOT_MATCH);
+    return false;
+  }
+
+  /**
+   * Add event listener for form input
+   * @param {Function} handler The function need to be set event
+   */
+  addHandlerForm(handler) {
+    this.parentElement.addEventListener('submit', (e) => {
+      e.preventDefault();
+      this.clearErrorMessage();
+      handler();
+    });
+  }
+
+  /**
+   * Show error style input password
+   */
+  changeToStyleErrorInputPassword() {
+    // Index = 1 because it should skip email input field
+    for (let index = 1; index < this.inputField.length; index += 1) {
+      this.inputField[index].style.background = '#ffc3c3';
+      this.inputField[index].style.borderColor = '#ce1414';
+    }
+  }
+
+  /**
+   * Clear error style input password
+   */
+  clearStyleErrorInputPassword() {
+    for (let index = 1; index < this.inputField.length; index += 1) {
+      this.inputField[index].style.background = '#f5f5f5';
+      this.inputField[index].style.borderColor = '#f5f5f5';
+    }
+  }
+
+  /**
+   * Reassign again to check error message element haved on page or not
+   */
+  reassignVariableErrorMessage() {
+    this.errorMessage = document.querySelector('.form__error-message');
+  }
+
+  /**
+   * Clear error message at form
+   */
+  clearErrorMessage() {
+    this.reassignVariableErrorMessage();
+
+    // If have error message on page, remove it
+    if (this.errorMessage) {
+      this.errorMessage.remove();
+      this.clearStyleErrorInputPassword();
+    }
+  }
+
+  /**
+   * Add event listener for input field at form
+   */
+  addHandlerInputFormChange() {
+    this.parentElement.addEventListener('input', () => {
+      this.clearErrorMessage();
+    });
+  }
+
+  /**
+   * Show error message with error style input password.
+   * @param {string} message The error message you want show in form.
+   */
+  showError(message) {
+    this.renderError(message);
+    this.changeToStyleErrorInputPassword();
+  }
+
+  /**
+   * Implement register success popup in site
+   */
+  initRegisterSuccessPopup() {
+    const typePopup = CONSTANT.TYPE_POPUP.success;
+    const title = 'Register Commpleted';
+    const content = 'Please login to continue!';
+    const btnContent = 'OK';
+
+    this.initPopupContent(typePopup, title, content, btnContent);
+  }
+
+  /**
+   * Implement error popup in site
+   * @param {string} content The content will show in error popup
+   */
+  initErrorPopup(content) {
+    const typePopup = CONSTANT.TYPE_POPUP.error;
+    const title = 'Error';
+    const btnContent = 'Got it!';
+
+    this.initPopupContent(typePopup, title, content, btnContent);
+  }
+
+  /**
+   * Show error message in form
+   * @param {*} message The message will show in form
+   */
+  renderError(message) {
+    const markup = `
+      <p class="form__error-message">${
+        !message ? this.messageDefault : message
+      }</p>
+    `;
+
+    document
+      .querySelector('.form__title')
+      .insertAdjacentHTML('afterend', markup);
+  }
+}
diff --git a/javascript-practice/src/js/views/view.js b/javascript-practice/src/js/views/view.js
new file mode 100644
index 0000000..a2a1675
--- /dev/null
+++ b/javascript-practice/src/js/views/view.js
@@ -0,0 +1,7 @@
+import RegisterView from './registerView';
+
+export default class View {
+  constructor() {
+    this.registerView = new RegisterView();
+  }
+}