React Essentials · Data Fetching · Lesson 18 of 26
Loading and Error States
Concept
Loading and Error States
Real apps track loading and error state alongside the data itself, so the UI can respond to all three cases.
By the end of this lesson
- Explain the core idea behind Loading and Error States.
- 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. Read one concept.
- 2. Change the example.
- 3. Run, compare, and explain.
- 4. Complete the challenge below.
ExampleRunnable
const [loading, setLoading] = useState(true);
const [error, setError] = useState(null);Self-check before continuing
Without looking at the example, describe what changes when you modify one input in Loading and Error States. 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
Render "Loading...", an error message, or the data depending on state.
Loading editor…
Console