Building a Dark Mode Toggle in React with Context API

Dark mode is a must-have feature in modern web apps. It enhances user experience and can reduce eye strain. In this post, we'll walk through how to implement a Dark Mode Toggle in a React app using the Context API to manage state globally.

We'll create a simple app where users can toggle between dark and light modes, with their preference stored in localStorage so it persists even after they leave or reload the page.

Step 1: Set up the Context

The first step is to create a ThemeContext that will provide the dark mode state and the toggle function to any component in the app.

// src/context/ThemeContext.js
import React, { createContext, useState, useEffect } from 'react';

export const ThemeContext = createContext();

export const ThemeProvider = ({ children }) => {
  const [darkMode, setDarkMode] = useState(() => {
    const savedMode = localStorage.getItem('dark-mode');
    return savedMode === 'true' || false;
  });

  useEffect(() => {
    localStorage.setItem('dark-mode', darkMode);
    document.body.className = darkMode ? 'dark-mode' : '';
  }, [darkMode]);

  const toggleDarkMode = () => {
    setDarkMode((prevMode) => !prevMode);
  };

  return (
    <ThemeContext.Provider value={{ darkMode, toggleDarkMode }}>
      {children}
    </ThemeContext.Provider>
  );
};

Here, we're using useState to initialize the theme based on localStorage. useEffect ensures that whenever the theme changes, it updates localStorageand applies the appropriate class to the body element.

---

Step 2: Create the Toggle Component

Here, we use useContext to consume the darkModevalue and toggleDarkMode function from the ThemeContext.

// src/components/ThemeToggle.js
import React, { useContext } from 'react';
import { ThemeContext } from '../context/ThemeContext';

const ThemeToggle = () => {
  const { darkMode, toggleDarkMode } = useContext(ThemeContext);

  return (
    <button onClick={toggleDarkMode}>
      {darkMode ? 'Switch to Light Mode' : 'Switch to Dark Mode'}
    </button>
  );
};

export default ThemeToggle;

---

Step 3: Apply Dark Mode Styles

To see the dark mode in action, you'll need to add some CSS styles. For simplicity, we'll apply a dark theme to the bodyelement.

/* src/styles.css */
body {
  margin: 0;
  font-family: sans-serif;
  transition: background-color 0.3s ease;
}

body.dark-mode {
  background-color: #121212;
  color: white;
}

---

Step 4: Set up the App Component

Here, we wrap the entire app inside the ThemeProvider, which allows the dark mode state and toggle function to be available globally.

// src/App.js
import React from 'react';
import { ThemeProvider } from './context/ThemeContext';
import ThemeToggle from './components/ThemeToggle';
import './styles.css';

function App() {
  return (
    <ThemeProvider>
      <div className="App">
        <h1>Dark Mode Toggle with Context API</h1>
        <ThemeToggle />
      </div>
    </ThemeProvider>
  );
}

export default App;

---

By using React's Context API, we made the dark mode state easily accessible across the app without prop-drilling. Adding localStorage ensures the theme preference persists, even after a page reload or revisit.

Feel free to tweak this basic implementation by adding more components and styles as per your needs.

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