How to use context api with react router v4?

In React Router v4, using the Context API enables us to pass data through the component tree without explicitly passing props through each component layer. Below, I'll provide a detailed example to illustrate how to implement this in React Router v4 and Context API.

First, let's assume we have a user authentication state that needs to be shared across multiple components. We'll create a Context to store this state and methods for manipulating it.

Step 1: Create Context

First, we need to create a new Context object.

javascript
import React, { createContext, useState } from 'react';

const AuthContext = createContext(null);

export default AuthContext;

Step 2: Create Provider

Next, we'll create a Provider component that wraps the top-level of our application and passes the Context's value to all child components.

javascript
import React, { useState } from 'react';
import AuthContext from './AuthContext';

const AuthProvider = ({ children }) => {
    const [isLoggedIn, setIsLoggedIn] = useState(false);

    const login = () => setIsLoggedIn(true);
    const logout = () => setIsLoggedIn(false);

    return (
        <AuthContext.Provider value={{ isLoggedIn, login, logout }}>
            {children}
        </AuthContext.Provider>
    );
}

export default AuthProvider;

Step 3: Use Provider in the Application

In your main application component, wrap the rest of the application with the newly created AuthProvider.

javascript
import React from 'react';
import ReactDOM from 'react-dom';
import { BrowserRouter as Router } from 'react-router-dom';
import App from './App';
import AuthProvider from './AuthProvider';

ReactDOM.render(
  <Router>
    <AuthProvider>
      <App />
    </AuthProvider>
  </Router>,
  document.getElementById('root')
);

Step 4: Use Context

In any child component, you can now use the useContext hook to access the isLoggedIn state and the login and logout methods.

javascript
import React, { useContext } from 'react';
import AuthContext from './AuthContext';

const LoginPage = () => {
    const { isLoggedIn, login } = useContext(AuthContext);

    return (
        <div>
            <p>{isLoggedIn ? 'You are logged in' : 'You are not logged in'}</p>
            <button onClick={() => login()}>Log in</button>
        </div>
    );
}

export default LoginPage;

By doing this, we can easily access and manipulate the user's login state throughout the application without having to pass props through multiple component layers, resulting in clearer and more maintainable code.