React 16.3: What’s New?

strict

StrictMode

import React from 'react';

function WokeAlarm() {
  return (
    <div>
      <Header />
      <React.StrictMode>
        <div>
          <SetAlarm />
          <RingAlarm />
        </div>
      </React.StrictMode>
      <Footer />
    </div>
  );
}

getDerivedStateFromProps

getSnapshotBeforeUpdate

componentWillMount

componentWillReceiveProps

componentWillUpdate

getDerivedStateFromProps

class Speaker extends Component {
  static getDerivedStateFromProps() {
    if (nextProps.value !== prevState.value) {
      return ({ value: nextProps.value });
    }
  }
}

getSnapshotBeforeUpdate

componentDidUpdate

...
getSnapShotBeforeUpdate(prevProps, prevState) {
  return prevProps.list.length < this.props.list.length ? this.listRef.scrollHeight : null;
}

componentDidUpdate(prevProps, prevState, snapshot) {
  if (snapshot !== null) {
    const listRef = this.listRef;
    listRef.scrollTop += listRef.scrollHeight - snapshot;
  }
}
...

forwardRef

ref

ref

import React, { Component } from 'react';

const LoginButton = React.forwardRef((props, ref) => (
  <button ref={ref} class="Login"> {props.children} </button>
));


class Display extends Component {
  myRef = React.createRef();

  componentDidMount() {
    this.myRef.current.focus();
  }

  render() {
    return (
      <div className="container">
        <LoginButton ref={this.myRef}> Get In! </LoginButton>
      </div>
    )
  }
}

forwardRef

createRef

class SpeakerComponent extends React.Component {
  constructor(props) {
    super(props);
  }

  render() {
    return <input type="text" ref={(input) => {
      this.inputRef = input;
    }} />;
  }
}

class SpeakerComponent extends React.Component {
  constructor(props) {
    super(props);

    this.inputRef = React.createRef();
  }

  render() {
    return <input type="text" ref={this.inputRef} />;
  }

  componentDidMount() {
    this.inputRef.current.focus();
  }
}

Context

import React, { Component } from 'react';

const Dog = (props) => (
  <div>
    <Animal name={props.name} />
  </div>
);

}
class Animal extends Component {
  render() {
    return (
      <div>
        <p> Hey, I'm a {this.props.name} </p>
      </div>
    )
  }
}


class App extends Component {
  state = {
    name: 'Casanova',
    food: 'bone',
  }

  render() {
    return (
      <div>
        <Dog name={this.state.name} />
      </div>
    )
  }
}

export default App;

import React, { Component } from 'react';

// create a new context
const MyContext = React.createContext();

// create a provider component
class MyProvider extents Component {
  state = {
    name: 'Casanova',
    food: 'bone'
  }

  render() {
    return (
      
      <MyContext.Provider value={{ state: this.state }}>
        { this.props.children }
      </MyContext.Provider>
      
    )
  }
}

const Dog = (props) => (
  <div>
    <Animal />
  </div>
);

class Animal extends Component {
  render() {
    return (
      <div>
        <MyContext.Consumer>
          {(context) => (
            <React.Fragment>
              <h3> Food: { context.state.food } </h3>
              <h3> Name: { context.state.name } </h3>
            </React.Fragment>
          )}
        </MyContext.Consumer>
      </div>
    )
  }
}

class App extends Component {
  render() {
    return (
      <MyProvider>
        <div>
          <Dog />
        </div>
      </MyProvider>
    )
  }
}

export default App;

<MyProvider />

<App />

<MyContext.Consumer />

Aside: Securing React Apps with Auth0

As you will learn in this section, you can easily secure your React applications with Auth0, a global leader in Identity-as-a-Service (IDaaS) that provides thousands of enterprise customers with modern identity solutions. Alongside with the classic username and password authentication process, Auth0 allows you to add features like Social Login, Multifactor Authentication, Passwordless Login, and much more with just a few clicks.

To follow along the instruction describe here, you will need an Auth0 account. If you don't have one yet, now is a good time to sign up for a free Auth0 account.

Also, if you want to follow this section in a clean environment, you can easily create a new React application with just one command:

npx create-react-app react-auth0

Then, you can move into your new React app (which was created inside a new directory called

react-auth0

by the

create-react-app

tool), and start working as explained in the following subsections.

Setting Up an Auth0 Application

To represent your React application in your Auth0 account, you will need to create an Auth0 Application. So, head to the Applications section on your Auth0 dashboard and proceed as follows:

1. click on the Create Application button;
2. then define a Name to your new application (e.g., "React Demo");
3. then select Single Page Web Applications as its type.
4. and hit the Create button to end the process.

After creating your application, Auth0 will redirect you to its Quick Start tab. From there, you will have to click on the Settings tab to whitelist some URLs that Auth0 can call after the authentication process. This is a security measure implemented by Auth0 to avoid the leaking of sensitive data (like ID Tokens).

So, when you arrive at the Settings tab, search for the Allowed Callback URLs field and add

http://localhost:3000/callback

into it. For this tutorial, this single URL will suffice.

That's it! From the Auth0 perspective, you are good to go and can start securing your React application.

Dependencies and Setup

To secure your React application with Auth0, there are only three dependencies that you will need to install:

• auth0.js

  : This is the default library to integrate web applications with Auth0.

• react-router

  : This is the de-facto library when it comes to routing management in React.

• react-router-dom

  : This is the extension to the previous library to web applications.

To install these dependencies, move into your project root and issue the following command:

npm install --save auth0-js react-router react-router-dom

Note: As you want the best security available, you are going to rely on the Auth0 login page. This method consists of redirecting users to a login page hosted by Auth0 that is easily customizable right from your Auth0 dashboard. If you want to learn why this is the best approach, check the Universal vs. Embedded Login article.

After installing all three libraries, you can create a service to handle the authentication process. You can call this service

Auth

and create it in the

src/Auth/

directory with the following code:

// src/Auth/Auth.js
import auth0 from 'auth0-js';

export default class Auth {
  constructor() {
    this.auth0 = new auth0.WebAuth({
      // the following three lines MUST be updated
      domain: '<AUTH0_DOMAIN>',
      audience: 'https://<AUTH0_DOMAIN>/userinfo',
      clientID: '<AUTH0_CLIENT_ID>',
      redirectUri: 'http://localhost:3000/callback',
      responseType: 'token id_token',
      scope: 'openid profile',
    });

    this.getProfile = this.getProfile.bind(this);
    this.handleAuthentication = this.handleAuthentication.bind(this);
    this.isAuthenticated = this.isAuthenticated.bind(this);
    this.login = this.login.bind(this);
    this.logout = this.logout.bind(this);
    this.setSession = this.setSession.bind(this);
  }

  getProfile() {
    return this.profile;
  }

  handleAuthentication() {
    return new Promise((resolve, reject) => {
      this.auth0.parseHash((err, authResult) => {
        if (err) return reject(err);
        console.log(authResult);
        if (!authResult || !authResult.idToken) {
          return reject(err);
        }
        this.setSession(authResult);
        resolve();
      });
    });
  }

  isAuthenticated() {
    return new Date().getTime() < this.expiresAt;
  }

  login() {
    this.auth0.authorize();
  }

  logout() {
    // clear id token and expiration
    this.idToken = null;
    this.expiresAt = null;
  }

  setSession(authResult) {
    this.idToken = authResult.idToken;
    this.profile = authResult.idTokenPayload;
    // set the time that the id token will expire at
    this.expiresAt = authResult.expiresIn * 1000 + new Date().getTime();
  }
}

The

Auth

service that you just created contains functions to deal with different steps of the sign in/sign up process. The following list briefly summarizes these functions and what they do:

• getProfile

  : This function returns the profile of the logged-in user.

• handleAuthentication

  : This function looks for the result of the authentication process in the URL hash. Then, the function processes the result with the

  parseHash

  method from

  auth0-js

  .

• isAuthenticated

  : This function checks whether the expiry time for the user's ID token has passed.

• login

  : This function initiates the login process, redirecting users to the login page.

• logout

  : This function removes the user's tokens and expiry time.

• setSession

  : This function sets the user's ID token, profile, and expiry time.

Besides these functions, the class contains a field called

auth0

that is initialized with values extracted from your Auth0 application. It is important to keep in mind that you have to replace the

<AUTH0_DOMAIN>

and

<AUTH0_CLIENT_ID>

placeholders that you are passing to the

auth0

field.

Note: For the

<AUTH0_DOMAIN>

placeholders, you will have to replace them with something similar to

your-subdomain.auth0.com

, where

your-subdomain

is the subdomain you chose while creating your Auth0 account (or your Auth0 tenant). For the

<AUTH0_CLIENT_ID>

, you will have to replace it with the random string copied from the Client ID field of the Auth0 Application you created previously.

Since you are using the Auth0 login page, your users are taken away from the application. However, after they authenticate, users automatically return to the callback URL that you set up previously (i.e.,

http://localhost:3000/callback

). This means that you need to create a component responsible for this route.

So, create a new file called

Callback.js

inside

src/Callback

(i.e., you will need to create the

Callback

directory) and insert the following code into it:

// src/Callback/Callback.js
import React from 'react';
import { withRouter } from 'react-router';

function Callback(props) {
  props.auth.handleAuthentication().then(() => {
    props.history.push('/');
  });

  return <div>Loading user profile.</div>;
}

export default withRouter(Callback);

This component, as you can see, is responsible for triggering the

handleAuthentication

process and, when the process ends, for pushing users to your home page. While this component processes the authentication result, it simply shows a message saying that it is loading the user profile.

After creating the

Auth

service and the

Callback

component, you can refactor your

App

component to integrate everything together:

// src/App.js

import React from 'react';
import { withRouter } from 'react-router';
import { Route } from 'react-router-dom';
import Callback from './Callback/Callback';
import './App.css';

function HomePage(props) {
  const { authenticated } = props;

  const logout = () => {
    props.auth.logout();
    props.history.push('/');
  };

  if (authenticated) {
    const { name } = props.auth.getProfile();
    return (
      <div>
        <h1>Howdy! Glad to see you back, {name}.</h1>
        <button onClick={logout}>Log out</button>
      </div>
    );
  }

  return (
    <div>
      <h1>I don't know you. Please, log in.</h1>
      <button onClick={props.auth.login}>Log in</button>
    </div>
  );
}

function App(props) {
  const authenticated = props.auth.isAuthenticated();

  return (
    <div className="App">
      <Route
        exact
        path="/callback"
        render={() => <Callback auth={props.auth} />}
      />
      <Route
        exact
        path="/"
        render={() => (
          <HomePage
            authenticated={authenticated}
            auth={props.auth}
            history={props.history}
          />
        )}
      />
    </div>
  );
}

export default withRouter(App);

In this case, you are actually defining two components inside the same file (just for the sake of simplicity). You are defining a

HomePage

component that shows a message with the name of the logged-in user (that is, when the user is logged in, of course), and a message telling unauthenticated users to log in.

Also, this file is making the

App

component responsible for deciding what component it must render. If the user is requesting the home page (i.e., the

/

route), the

HomePage

component is shown. If the user is requesting the callback page (i.e.,

/callback

), then the

Callback

component is shown.

Note that you are using the

Auth

service in all your components (

App

,

HomePage

, and

Callback

) and also inside the

Auth

service. As such, you need to have a global instance for this service, and you have to include it in your

App

component.

So, to create this global

Auth

instance and to wrap things up, you will need to update your

index.js

file as shown here:

// src/index.js

import React from 'react';
import ReactDOM from 'react-dom';
import { BrowserRouter } from 'react-router-dom';
import Auth from './Auth/Auth';
import './index.css';
import App from './App';
import registerServiceWorker from './registerServiceWorker';

const auth = new Auth();

ReactDOM.render(
  <BrowserRouter>
    <App auth={auth} />
  </BrowserRouter>,
  document.getElementById('root'),
);
registerServiceWorker();

After that, you are done! You just finished securing your React application with Auth0. If you take your app for a spin now (

npm start

), you will be able to authenticate yourself with the help of Auth0, and you will be able to see your React app show your name (that is, if your identity provider does provide a name).

If you are interested in learning more, please, refer to the official React Quick Start guide to see, step by step, how to properly secure a React application. Besides the steps shown in this section, the guide also shows:

• How to manage profile information of authenticated users.
• How to properly call an API.
• How to control which routes users can see/interact with.
• How to deal with the expiry time of users' tokens.