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Migrating from useState to useReducer, Building a Counter in a Next.js App

Updated: at 05:05 PM

Introduction

In this tutorial, we will demonstrate how to migrate from using useState to useReducer when creating a counter interface that allows you to increment, decrement, and reset the count value. This article is tailored for intermediate React developers looking to expand their knowledge of React hooks.

We will start by creating a new Next.js app using npx as our foundation.

Prerequisites

Step 1: Create a Next.js App

Open your terminal and run the following command to create a new Next.js app:

npx create-next-app counter-app

This will create a new directory called counter-app with a basic Next.js project structure. Navigate to the new directory:

cd counter-app

Step 2: Implement the Counter with useState

Before migrating to useReducer, let’s create a simple counter using useState. Open the pages/index.js file and replace its content with the following code:

import { useState } from 'react';

export default function Home() {
  const [count, setCount] = useState(0);

  const increment = () => setCount(count + 1);
  const decrement = () => setCount(count - 1);
  const reset = () => setCount(0);

  return (
    <div>
      <h1>Counter: {count}</h1>
      <button onClick={increment}>Increment</button>
      <button onClick={decrement}>Decrement</button>
      <button onClick={reset}>Reset</button>
    </div>
  );
}

Step 3: Migrate to useReducer

Now, we’ll migrate the code to use useReducer instead of useState. First, import useReducer at the top of the index.js file:

import { useReducer } from 'react';

Next, define the reducer function and the initial state:

const initialState = { count: 0 };

function reducer(state, action) {
  switch (action.type) {
    case 'increment':
      return { count: state.count + 1 };
    case 'decrement':
      return { count: state.count - 1 };
    case 'reset':
      return initialState;
    default:
      throw new Error('Unknown action type');
  }
}

Now, replace the useState hook with the useReducer hook:

const [state, dispatch] = useReducer(reducer, initialState);

Finally, update the event handlers to use dispatch:

const increment = () => dispatch({ type: 'increment' });
const decrement = () => dispatch({ type: 'decrement' });
const reset = () => dispatch({ type: 'reset' });

And update the count display to use state.count instead of count:

<h1>Counter: {state.count}</h1>

Here’s the complete code:

import { useReducer } from 'react';

const initialState = { count: 0 };

function reducer(state, action) {
  switch (action.type) {
    case 'increment':
      return { count: state.count + 1 };
    case 'decrement':
      return { count: state.count - 1 };
    case 'reset':
      return initialState;
    default:
      throw new Error('Unknown action type');
  }
}

export default function Home() {
  const [state, dispatch] = useReducer(reducer, initialState);

  const increment = () => dispatch({ type: 'increment' }); const decrement = () => dispatch({ type: 'decrement' }); const reset = () => dispatch({ type: 'reset' });

  return ( 
    <div> 
      <h1>Counter: {state.count}</h1>
      <button onClick={increment}>Increment</button> 
      <button onClick={decrement}>Decrement</button> 
      <button onClick={reset}>Reset</button> 
    </div>
  ); 
}

Step 4: Run the App

Start the development server by running the following command:

npm run dev

Open your browser and navigate to http://localhost:3000. You should now see the counter interface with buttons to increment, decrement, and reset the count value.

Conclusion

In this tutorial, we demonstrated how to migrate from useState to useReducer when creating a counter interface in a Next.js app.

Additional Tips

Now that you have successfully migrated from useState to useReducer, here are some additional tips to further enhance your React development skills.

  1. Extract the Reducer to a Separate File

As your application grows in complexity, it’s a good practice to keep your code modular by extracting the reducer function to a separate file. You can then import it in any component that requires it.

Create a new file called reducer.js in your counter-app directory and move the reducer function and the initial state to that file:

// reducer.js
export const initialState = { count: 0 };

export function reducer(state, action) {
  switch (action.type) {
    case 'increment':
      return { count: state.count + 1 };
    case 'decrement':
      return { count: state.count - 1 };
    case 'reset':
      return initialState;
    default:
      throw new Error('Unknown action type');
  }
}

Then, import the reducer and initialState in your index.js file:

import { useReducer } from 'react';
import { reducer, initialState } from './reducer';

// ... rest of the component code
  1. Use Context API for Global State

If you need to share the counter state across multiple components, consider using the Context API. It will allow you to provide and consume the state without the need to pass it down through props.

  1. Add Custom Middleware

When using useReducer, you can add custom middleware to handle side effects, logging, or any other functionality that should be triggered when dispatching actions. This can be particularly useful in more complex applications.

  1. Explore Other Hooks

React has a variety of built-in hooks that can help you manage state, side effects, and other aspects of your components. Some common hooks include useEffect, useMemo, and useRef. Familiarize yourself with these hooks and experiment with them to improve your components.

By applying these additional tips and exploring the capabilities of React hooks, you’ll be well-equipped to tackle more complex scenarios in your React applications.