Form validation and errors

What this means

Validation checks whether input is acceptable. A beginner-friendly form shows what is wrong, where it is wrong, and how to fix it.

In beginner terms, this topic answers one practical question: "What should I write, and why does React care about it?" Do not try to memorize the syntax first. First understand the idea, then connect the syntax to that idea.

Why it matters

Good validation prevents confusion. Instead of silently failing, the UI can say Email is required or Password must be at least 8 characters.

When you build real React screens, this idea helps you decide where data should live, what the user should see, and what should happen after an interaction. That is why this lesson is part of the main path instead of being an optional detail.

Step by step

1. Notice the UI problem this topic solves. 2. Look at the smallest possible example. 3. Change one value and predict what should appear. 4. Run the example and compare the result with your prediction. 5. Use the practice task before moving on.

Small example

if (!email) {
  setError("Email is required");
}

Common mistake

Do not show vague errors like Invalid input when you can explain the exact problem.

Practice task

Create a form that shows Name is required when the name field is empty.

Remember this

Validation should guide the user, not blame them.