## What is State Management?
State management is handling data that changes over time in your application - user input, API responses, authentication status, shopping cart items.
In small apps, local component state works fine. In complex apps with dozens of components sharing data, you need a better approach.
## Why It Matters
**The Problem**: In apps like Slack or e-commerce sites, many components need the same data. Without proper management:
- **Prop Drilling**: Passing data through 5 layers of components
- **Inconsistent State**: Same data stored in multiple places gets out of sync
- **Hard to Debug**: Cannot track where state changes happen
## Types of State
**Local State**: Data for a single component (form input, dropdown open/closed)
```javascript
const [count, setCount] = useState(0);
```
**Shared State**: Data multiple components need (user authentication, theme, shopping cart)
**Server State**: Data from APIs (products, user profiles). Special because it needs loading states, caching, error handling.
## The Main Solutions
**React Context** - Built into React, good for simple global state:
```javascript
const UserContext = createContext();
// Any component can access
const { user } = useContext(UserContext);
```
**Redux** - Popular for complex apps with lots of shared state. Centralizes everything in one place.
**Zustand** - Simpler than Redux, minimal boilerplate, easy to learn.
**React Query** - Specialized for API data. Handles caching, loading states, refetching automatically.
## Choosing the Right Tool
**Use Local State** when data is only needed in one component
**Use Context** for simple global data (theme, language, auth status)
**Use Redux** for large apps with complex state interactions
**Use React Query** when most state comes from APIs
Most real apps use **multiple approaches** depending on the type of data.
## Real-World Example: E-Commerce
- **Local State**: Image carousel index, filter dropdown state
- **Context**: User authentication, theme preference
- **Redux/Zustand**: Shopping cart, checkout process
- **React Query**: Product listings, order details from API
## Common Mistakes
**Global State Overuse**: Not everything needs global state. Keep state as local as possible.
**Wrong Tool**: Using Redux for simple apps leads to unnecessary complexity.
**No Server State Solution**: Manually managing API data with useState leads to bugs. Use React Query.
## The Modern Approach
**Use the simplest solution that solves your problem.** Do not reach for Redux because it is popular. Start simple, add complexity only when needed.
State management is not about choosing the "best" library - it is understanding your app needs and picking the right tool for each type of state.
