React Essentials · Forms & Events · Lesson 15 of 26
Validating Input
Concept
Validating Input
Simple validation checks values before allowing submission and shows an error message when something is wrong.
By the end of this lesson
- Explain the core idea behind Validating Input.
- 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.
Self-check before continuing
Without looking at the example, describe what changes when you modify one input in Validating Input. 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
Add validation that blocks submission if a password field is empty.
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Console