Advanced React
Concepts: Enhancing Your Application

As React evolves, developers need to utilize advanced patterns to create efficient, maintainable applications. This guide explores key concepts including Higher-Order Components (HOCs), Render Props, the Context API, and performance optimization techniques.

A Higher-Order Component is a function that takes a component and returns a new component. It can provide additional props or features to the wrapped component.

const withExtraFunctionality = (WrappedComponent) => {
  return (props) => {
    // Logic to add extra functionality

    return <WrappedComponent {...props} />;
  };
};

Render Props is a technique for sharing code between components using a function that returns a React element.

Example:

Here’s a simple example using a toggle button.

import React, { useState } from 'react';

const Toggle = ({ render }) => {
  const [isOn, setIsOn] = useState(false);

  const toggle = () => {
    setIsOn((prevState) => !prevState);
  };

  return render({ isOn, toggle });
};

export default Toggle;

The Context API is a way to share values (like state) between components without having to pass props manually at every level.

Example:

Let’s use context to provide user info globally.

// UserContext.js
import React, { createContext, useState } from 'react';

// Create the context
const UserContext = createContext();

// Create the provider component
export const UserProvider = ({ children }) => {
  const [user, setUser] = useState({
    username: 'JohnDoe',
    email: 'johndoe@example.com',
  });

  const updateUser = (newUserData) => {
    setUser((prevUser) => ({
      ...prevUser,
      ...newUserData,
    }));
  };

  return (
    <UserContext.Provider value={{ user, updateUser }}>
      {children}
    </UserContext.Provider>
  );
};

export default UserContext;
// index.js or App.js
import React from 'react';
import ReactDOM from 'react-dom';
import App from './App';
import { UserProvider } from './UserContext';

ReactDOM.render(
  <UserProvider>
    <App />
  </UserProvider>,
  document.getElementById('root')
);
// Profile.js
import React, { useContext, useState } from 'react';
import UserContext from './UserContext';

const Profile = () => {
  const { user, updateUser } = useContext(UserContext);
  const [newUsername, setNewUsername] = useState('');

  const handleUpdate = () => {
    updateUser({ username: newUsername });
    setNewUsername(''); // Clear the input
  };

  return (
    <div>
      <h2>User Profile</h2>
      <p>Username: {user.username}</p>
      <p>Email: {user.email}</p>

      <input
        type="text"
        value={newUsername}
        onChange={(e) => setNewUsername(e.target.value)}
        placeholder="New Username"
      />
      <button onClick={handleUpdate}>Update Username</button>
    </div>
  );
};

export default Profile;

React.memo is a way to optimize functional components by preventing them from re-rendering if their props haven’t changed.

Example:

Let’s create a simple component that only re-renders when the count changes.
In this example, CounterDisplay will only render when count changes, improving performance by avoiding unnecessary renders.

import React, { useState } from 'react';

// CounterDisplay component wrapped with React.memo
const CounterDisplay = React.memo(({ count }) => {
  console.log('CounterDisplay rendered');
  return <h2>Count: {count}</h2>;
});

const App = () => {
  const [count, setCount] = useState(0);
  const [name, setName] = useState('');

  const incrementCount = () => {
    setCount(count + 1);
  };

  const handleNameChange = (e) => {
    setName(e.target.value);
  };

  return (
    <div>
      <CounterDisplay count={count} />
      <button onClick={incrementCount}>Increment Count</button>

      <div>
        <input
          type="text"
          value={name}
          onChange={handleNameChange}
          placeholder="Enter your name"
        />
        <p>Your name is: {name}</p>
      </div>
    </div>
  );
};

export default App;

These simplified examples show how to use Higher-Order Components, Render Props, the Context API, and React.memo for optimization in React. By understanding and applying these concepts, you can build more efficient and maintainable React applications.