Context performance

What this means

When a context value changes, components reading that context may render again. Large context values that change often can make updates harder to control.

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

Understanding this keeps you from putting everything into one giant app context. Smaller contexts or local state are often better.

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 value = React.useMemo(() => ({ user, logout }), [user]);

Common mistake

Do not store fast-changing local input state in a global context unless many distant components truly need it.

Practice task

Decide whether theme, search text, and current user should be local state or context.

Remember this

Use context for shared state, not all state.