React Hooks tutorial: Build a to-do list with React Hooks

With the release of React 16.8 in 2019, React Hooks finally became available for use in production applications. This allows React developers to make functional components stateful. Instead of using a class component to hold stateful logic, we can use functional components.

Have you ever struggled with managing state in React class components or found your code cluttered with life cycle methods? React Hooks simplifies state management and streamlines the component-building process. They are a powerful tool; we’ll start by building a to-do list to better understand them, specifically focusing on the useState hook.

Note: It is assumed you already know at least the basics of React. If you’re new to learning React, that’s okay. Check out our React tutorial for beginners before continuing here.

Overview of React Hooks#

In React, hooks allow you to hook into React state and life cycle features from function components. This allows you to use React without classes.

When you take an initial look at the React Hooks documentation, you’ll see that there are several hooks that we can use for our applications. You can even create your own. Some of the popular ones include:

• useState: Adds state to functional components.

• useEffect: Performs side effects in function components.

• useContext: Accepts a context object and returns the current context value.

• useCallback: Returns a memoized callback.

Benefits of using hooks#

React Hooks offers several advantages that can improve the structure and maintainability of our application. Here are some of the key benefits:

• Hooks enable you to manage state and side effects in functional components, eliminating the need for class components.

• Stateful logic implemented with hooks is easier to isolate and test, as it doesn’t depend on the React life cycle or class-based structure.

• You can share logic between components without using props or higher-order components.

• Hooks separate logic based on its purpose (e.g., state, side effects) rather than splitting it by life cycle methods, leading to cleaner and more maintainable code.

The only hook we’ll need for this to-do list project is the useState hook. This hook replaces the need for a state object in a class component structure.

The class component in React #

When looking at older React legacy code, you will see something like the following:

The class component structure describes an instance of an App object with a state that is an array of movies. We render that array of movies by mapping over the state object and returning every movie within its own <div> element.

Functional components in React #

Stateful functional components are very similar in that they hold state but are much simpler. Look at the following example:

The useState hook is deconstructed into an array with two items in it:

• The variable that holds our state (movies)

• A method that is used to update that state if you need to (setMovies)

The useState hook creates and initializes a local state, movies, within the App component and ensures that the App component will rerender whenever setMovies is called. This way, any changes to movies will immediately appear in the component’s output.

Now that you have the basic idea behind the useState React Hook, let’s see how to use it when creating a to-do list application.

React to-do list#

Our goal is to create a to-do list UI with the following components:

1. Header: Labels the to-do list.

2. To-do items list: Displays each to-do item. We’ll also create two additional capabilities for the list:

   1. Ability to strike through a task that indicates completion.

   2. Remove all completed tasks from the list with a button click.

3. Form: Adds new to-do task item to the list.

The final layout of the application that we’ll create will look something like this:

Let’s start with a step-by-step guide on creating a to-do list in React using the useState hook.

Step 1: Create a React application#

The first step is to create a React application. You can use either Yarn or npm to set up your React project:

Navigate into the todo-list folder and start the application. Your project should now be running on http://localhost:3000.

Step 2: Set up the App component#

Navigate to the App.js file and clear the existing content inside the <div> tags. We won’t need any of the prepopulated codes. The App.js file should look something like this:

Step 3: Create the Header component#

A header enhances the application’s UI by clearly indicating its purpose. We’ll create a reusable Header component.

Create a new file, Header.js, in the src directory. Inside this file, create a functional component, Header, that returns JSX to render the header section. The JSX should display a header identifying your application’s name. Finally, export your Header component and import it to App.js.

Step 4: Add the mock data#

To ensure our app behaves as expected before connecting to a real API, we’ll use mock data to simulate tasks and test our application. This helps us focus on the core functionality without worrying about backend integration.

For this, create a file, data.json, in the src directory. Populate the data.json file with sample tasks using the JSON data given below:

Each task is an object with id, task, and complete properties.

• id: It is a unique identifier for each task, crucial for React’s list rendering.

• task: It is the description of the to-do item.

• complete: It is a boolean indicating whether the task is completed.

You also need to import the mock data from the data.json file in the App.js file.

Step 5: Read the list of to-do items and display them#

Now that we have our data and header set up, we’ll create components to display the list of tasks. The first thing to do here is initializing a new state in the App component using the useState hook. This state will store our mock data for the component.

The basic syntax for the useState() hook#

We’ll create a new state, toDoList, and initialize it with the imported mock data. It will hold the current list of tasks, and setToDoList will be used to update this state.

Now, we need to map over the toDoList state to render each to-do item in our application. We’ll create two components to display the list of tasks.

Create two new files, ToDoList.js and ToDo.js in the src directory. The ToDoList.js file will have a component—ToDoList—that will serve as the container that holds all of our todos, and the ToDo.js file will have a component—ToDo— that will render an individual to-do item in our To-do list.

Let’s first look at the ToDoList.js file. In this file, we have the ToDoList component that receives toDoList as a prop from the parent component—App.js. It then iterates over the toDoList array and renders a ToDo component for each task. It also assigns a unique key to each ToDo component using the task’s id to help React optimize rendering.

Now, let’s look at the ToDo.js file. In this file, we have the ToDo component, which receives a single todo object as a prop and renders the task property of the todo object.

Now that both the components are set, we must import and use the ToDoList component in the App.js file.

Run the code above, and you should now see the “To Do List” header followed by a list of tasks, each displayed within its own row.

Step 6: Toggle task completion#

We’ll allow users to mark tasks as complete or incomplete by clicking on them. Completed tasks will be visually distinguished with a strike-through.

We’ll update the ToDo.js file to conditionally apply a CSS class based on the task’s completion status. We add the attribute className that conditionally applies the strike class if todo.complete is true, otherwise applies no class.

Note: Anything in between curly braces when using JSX signals that we are using JavaScript functions.

In the styles.css file, we add the strike class which applies a line-through to indicate completion, and changes the text color to gray for better visibility.

If you were to look at your React application, you would see some tasks with a line indicating that a project or task has been completed.

Next, we have to create a function, handleToggle, that will toggle the complete status of a task. As our state resides there, we’ll implement this function in the App.js file.

The handleToggle function accepts an id, maps through the toDoList, and toggles the complete status of the matching task, marking that task as complete or incomplete. We’ll use setToDoList to update the state with the modified task list, triggering a rerender.

Note: setToDoList(updatedList) is analogous to this.setState({ toDoList: updatedList }) would have been used if we had worked with the state in class components.

We now need to pass handleToggle function to ToDoList and ToDo components. Once done, click any task to toggle its completion status. Completed tasks should display with a strike-through and gray color, while incomplete tasks remain normal. If you double-click the task, it will be marked as incomplete, depicting the change in the toggle state.

Step 7: Clear completed tasks#

What will we do with all those crossed-off, completed tasks? Let’s remove them from the list. We’ll create a button with an onClick handler that filters out all of the completed items.

This functionality is similar to the toggle functionality we just did. We’ll create a function, handleFilter that will filter out tasks where complete is true, effectively removing all completed tasks from the list. It will then update the toDoList state with the filtered list, triggering a rerender.

We’ll then pass the handleFilter function to the ToDoList component.

Note: The JavaScript filter method returns a new array, so we are not in danger of mutating the state and can proceed without copying the array before we play with it.

Then, in the ToDoList component, we’ll add a button labeled “Clear Completed” below the list of tasks and set an onClick to fire the handleFilter function.

To test the functionality, mark a few tasks as complete by clicking on them. Then click the “Clear Completed” button to remove all completed tasks from the list.

Step 8: Add new tasks with a form#

The final step in our list is to create a form component for adding tasks to our to-do list. We’ll create a new file, ToDoForm.js, in the src directory for this.

In this file, a ToDoForm component will create a basic form allowing a user to input a task name and click a button to add the new task to the list. For a form to work correctly, we must keep track of the changes as we go, so logically, we have to handle what happens as the input changes.

The ToDoForm component will have the following:

1. A state, userInput, will track any input the user types into their form.

2. A function, handleChange, will handle the local state’s changes. When a user types in the input box, the state will reflect the most recent input.

3. A function, handleSubmit, is the default form submission behavior. It also checks if the input is not empty or has white space. It then calls an addTask function passed via props to add the new task (discussed later). Finally, it resets the input field to an empty string after submission.

Note: Remember to use e.preventDefault() when we use forms because we don’t want the default action to occur. In this case, it would reload the page, and everything changed will return to how it was initially rendered.

4. A form container with an input field should have a value associated with it that matches the name of your state variable. It will also have a button that will call the relevant event handler to create the task.

With the ToDoForm component setup, we need to create the addTask function in the App component since that is where our toDoList state is. We need to be able to set the new array on state using setToDoList, and we can only do that when the addTask function has access to that state.

This function takes in userInput that we gathered from our form component’s current state. It then creates a new task object with a unique id and the task description from user input and sets complete to false. It uses the spread operator (...) to add the new task to the existing toDoList array, ensuring immutability.

Lastly, we’ll import the ToDoForm component in the App component and pass the addTask function as a prop.

Complete application#

Here is the complete to-do application with the functionality of creating and adding a new task to the to-do list.

What to learn next#

Congrats! You’ve now made a to-do list using the useState hooks. If you found this fairly straightforward, play around with the code and try to implement more functionality.

Here are some extra things you can do to give you some ideas:

• Add the ability to create a due date for each task or a priority rating.

• Give the ability to sort the list by the due date or priority.

• Create a backend so your to-do list can persist.

• Create a frontend interface for your own custom React app.

• Style application using React-Bootstrap or CSS-in-JS.

• Employ the Context API using the useContext hook instead of local state and props.

Continue learning the useState hook#

Explore these projects for hands-on practice on the useState hook to better understand managing state within functional components.

• Create a Trello Clone with React

• Build the Frontend of a Financial Application Using React

• Build a Location Tracker Using Leaflet, ReactJS, and Express.js