Why Go Beyond Components?

Until now we said state should be as close as possible to where it's used. But imagine a shopping cart in an online store. It's needed:

1. In the site header (product counter).
2. On the product page ( " Add " button).
3. In the cart sidebar.
4. On the checkout page.

If you try to " thread " the product list through props from the very top to the very bottom, your code will turn into a tangled knot of threads.

1. Analogy: Global Cloud

• Local State (useState): These are your personal thoughts. No one knows about them until you say.
• Global State: This is a common chat in Telegram or cloud storage. Any component (any " employee " ) can at any moment look into this cloud, take data or update it. And everyone else will instantly see changes.

2. Zustand: Modern Standard

For a long time, Redux dominated React — powerful but very complex and cumbersome. Zustand (German for " state " ) replaced it.

• Simplicity: You create a store in literally 10 lines of code.
• Scalability: It works equally well in small business cards and huge CRM systems.
• Performance: Only components that read a specific field ( " product count " ) will be updated. The rest of the site will continue " sleeping " .

3. Golden Rule: Where to Store Data?

Don't shove everything into global state. This is a typical beginner mistake.

1. Local State (useState): Data needed only here and now (text in input field, is dropdown open).
2. Server State (React Query): Data that came from the database (post list, user profile).
3. Global State (Zustand): Purely client data needed by the entire application (theme, cart, auth token).

Global state is your application's coordination center. It makes architecture predictable and clean.