Level Up React: Mastering useEffect for performant React applications

The useEffect hook is deceptively simple. Most React developers learn to use it early on, but few truly understand its inner workings. This knowledge gap can lead to subtle bugs, performance issues, and code that's difficult to maintain as your applications grow.

In my latest article in the "Level Up React" series, I dive deep into the complexities of useEffect and explore how to use it effectively in real-world scenarios.

What You'll Learn

✅ The actual execution cycle of useEffect (it's not when you might think!)

✅ How the dependency array works under the hood

✅ Common pitfalls that even experienced developers encounter

✅ When you should not use useEffect (and what to use instead)

✅ Practical techniques for synchronizing with external systems

✅ Testing components that use useEffect

A Glimpse Into the Article

One common mistake developers make is creating infinite loops with useEffect, especially when fetching data:

// ❌ Creating an infinite loop
function NotificationCenter() {
  const [notifications, setNotifications] = useState<Notification[]>([]);

  useEffect(() => {
    // Fetching notifications from the API
    fetchNotifications().then(newNotifications => {
      // This update triggers a new render
      setNotifications([...notifications, ...newNotifications]);
    });
  }, [notifications]); // notifications is a dependency

  return (
    <div className="notification-center">
      {notifications.map(notification => (
        <NotificationItem key={notification.id} data={notification} />
      ))}
    </div>
  );
}

In the article, I explain why this happens and show you how to fix it:

// ✅ Solution: Using the functional updater
function NotificationCenter() {
  const [notifications, setNotifications] = useState<Notification[]>([]);

  useEffect(() => {
    fetchNotifications().then(newNotifications => {
      // This form of setState doesn't need to depend on the current state
      setNotifications(prevNotifications => [
        ...prevNotifications,
        ...newNotifications
      ]);
    });
  }, []); // One-time execution at mounting
}

I also cover less obvious scenarios, like when you actually shouldn't use useEffect at all - something that even experienced React developers often miss.

Ready to Level Up?

This article is designed for React developers who want to go beyond the basics and truly understand how useEffect works under the hood. Whether you're dealing with complex data fetching, managing subscriptions, or synchronizing with external systems, mastering useEffect will help you write more predictable, performant, and maintainable React code.

👉 Read the full article here: https://www.56kode.com/posts/level-up-react-mastering-useeffect-for-performant-applications/