REACT.js Workshop


  • Presentation slides and example code
  • My implementation of the exercises
  • Feedback form


Exercise 1 - Components

In this exercise we are going to create a new React app and some components.

  1. Create a new React app by using the React create-react-template on CodeSandbox or locally using the create-react-app CLI command.

I recommend you use CodeSandbox ( because that does not require any setup so you can start right away.

  1. Create the following component hierarchy:
  • App
    • Header
    • Timeline
      • Post (1..n)

Note how these bullets resemble the parent-child relation between the components.

I recommend placing each component in a separate file.

  1. Let each component render a text or something so you can verify all components are there.
Exercise 2 - Props

In this exercise we will pass props between components.

  1. In the App component, define an array of post objects:
const posts = [ 
  { user: 'Bouwe', content: 'Hello World' }, 
  { user: 'Bouwe', content: 'My second tweet :)' } 

Although not necessary, feel free to change the user to your username (see the table at the bottom of this page) and enter your own content.

  1. Pass the array of post objects as props from App to Timeline.

  2. In the Timeline component, render a Post component for each post in the posts array using the function. Pass each post object as props to the Post component.

  3. In Post, render (display) the user and content of the post object from props

What we have now is an app that passes data to components using props. Each component only receives the data it needs to render its own piece of UI.

Exercise 3 - State

In this exercise we make the App component stateful so it can manage all posts on your timeline. Also we create a dummy button that adds random posts to state.

NOTE: We only update the App component in this exercise.

  1. Call useState and pass in an empty array as the initial state.

  2. Make sure you initialize the two variables useState returns.

  3. Remove the posts array we made in the previous exercise.

  4. Pass the posts variable useState returns as props to Timeline. (Although this might already be the case depending on how you named things.)

  5. Create a function within the App component: addPost(content)

  6. In this function create a post object containing the provided content and your username.

  7. Then call setPosts and provide an array containing both the new post object and the current posts.

TIP You might want to check the example code if you're not sure how to do this.

  1. For testing purposes, add a dummy button in the App component's JSX with an onClick to call the addPost function.
<button onClick={() => addPost("Hello World")}>Dummy</button>

What we have now is an app that is ready for adding posts.

Exercise 4 - Forms

In this exercise we'll create a new component, Compose, which contains a form that allows the user to create a new post.

  1. Create the Compose component that returns something to indicate it's the Compose component.

  2. Render the Compose component inside the App component

In the Compose component:

  1. Introduce a content variable with useState.

  2. In Compose, render the following form:

  <textarea value={content} />

Replace steps 3 and 4 by uncontrolled inputs if you prefer.

  1. For the textarea, implement an onChange event handler that calls setContent and passes the content state variable.

In the App component:

  1. Pass a reference to the addPost function as props to Compose

  2. Remove the dummy button

In the Compose component:

  1. Add an onSubmit event handler to the form which calls the addPost function from props and passes the content.

  2. Clear the textarea value after submitting

What we have now is an app that works! You can add posts that are rendered on the timeline. However, it's all local state... We need to communicate to a backend to persist the posts.

Exercise 5 - API calls

In this exercise we are going to communicate to the REST API so we can persist posts and retrieve the timeline.

TIP I recommend you use the axios library so you can use the example code I've shown you. However, any other HTTP client library will also suffice.

NOTE: the :userId is your username, check the table at the bottom of this page.

  1. In the App component, use the useEffect hook to retrieve the timeline by performing an HTTP GET on /users/:userId/timeline

Please do not forget the 2nd argument for useEffect: an empty array!

  1. Update the App's addPost function so it performs an HTTP POST on /users/:userId/posts.

TIP Check the example code for error handling, although you might also skip error handling to keep it simple.

EXERCISE 6 - Follow/unfollow users

In this exercise we are creating functionality for following and unfollowing other users.

Possible functionality:

  1. Show all users

  2. Indicate per user whether or not you are following him/her

  3. Add toggle button per user

  4. Toggling the button calls API to follow or unfollow the user

  5. Check the API documentation:

Implementation hints:

You could consider starting with refactoring the current code to avoid an even bigger and more complex App component. If you don't want that, skip to step 3 below.

Another optional step is to either display the following functionality next to the timeline on the same page or in a separate page. For the latter you need to implement some kind of conditional rendering or you could even use a routing library like React Router. If you don't want that, skip to step 6.

  1. Refactor all timeline related code and rendering the Compose and Timeline components into a new component: TimelineContainer

  2. Now App only renders the Header and TimelineContainer components.

  3. Create a placeholder FollowingContainer component.

  4. Add navigation to the Header component for either selecting the Timeline or Following page.

  5. Let App conditionally render either the TimelineContainer or the FollowingContainer.

  6. Implement the follow/unfollow functionality itself as described above or do it your own way.

User accounts for the API