RivoCode

React Essentials · Hooks · Lesson 9 of 26

useEffect for Side Effects

Concept

useEffect for Side Effects

useEffect runs code after render, which is perfect for data fetching, subscriptions, or syncing with something outside React.

By the end of this lesson
  • Explain the core idea behind useEffect for Side Effects.
  • Predict output before running a change.
  • Test one realistic and one unusual input.
  • Use the result to make the next decision.
How to study this page
  1. 1. Read one concept.
  2. 2. Change the example.
  3. 3. Run, compare, and explain.
  4. 4. Complete the challenge below.
ExampleRunnable
useEffect(() => {
  document.title = "RivoCode - " + count;
}, [count]);
Try it Yourself »
Self-check before continuing

Without looking at the example, describe what changes when you modify one input in useEffect for Side Effects. Then reopen the editor and prove your explanation with a small test.

You are ready to continue when you can predict, test, and explain the result.

Your turn

Use useEffect to log a message every time a count value changes.

Loading editor…

Console

Output will appear here...