Typing state

What this means

TypeScript can infer many useState types from the initial value. Sometimes you provide a type when the initial value is empty or nullable.

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

Typed state helps prevent impossible UI states, like treating a missing user as if it always exists.

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

const [user, setUser] = useState<User | null>(null);

Common mistake

Do not pretend nullable data is always present. Check for null before reading properties.

Practice task

Type a state value that starts as null and later stores a selected lesson.

Remember this

Types should match what can really happen.