Local state is like a private notebook kept by one small part of an app. Other parts of the app do not know about it and do not need to see it.

Your Personal Notebook

Global state acts like a shared bulletin board where every part of the app can read information. It is used for data that everyone needs to know.

A Public Bulletin Board

This happens when you have to pass a piece of information through many 'middlemen' who don't actually need it. Developers call this 'prop drilling,' and it can make an app messy.

The Relay Race Problem

Simple tasks like opening a menu or ticking a checkbox are usually local. These changes only matter to the specific button or box you are interacting with.

Small Private Changes

Important data like your username or a shopping cart is usually global. These details need to stay the same no matter which page you visit.

Information for Everyone

This means there is only one central place where the 'correct' version of data is kept. It ensures that if you change your name on one screen, it updates everywhere else too.

One Source of Truth

Keeping most things local prevents the global 'shared space' from becoming too cluttered. You should only share information that actually needs to be shared.

Avoiding Crowded Spaces

Local updates are very fast because only one tiny part of the app has to refresh. Updating global data can sometimes cause the entire app to 're-think' its layout.

The Speed of Updates

Use local state for temporary, small details that stay on one screen. Use global state for major information that follows the user throughout the whole app.