1. Introduction to State Management

State is one of the most essential concepts in React. It defines how an application's UI updates in response to user interactions over time.

State management involves:

1. Deciding when to create state

2. Determining what type of state is needed (local or global).

3. Deciding where to place state in the component hierarchy

4. Ensuring that data flows efficiently through the app.

Analogy: State management is like giving each piece of state a proper home within the React component tree.

2. Understanding Local vs. Global State

Each piece of state in React falls into one of two categories: Local State or Global State.

🔹 Local State

• Exists only within a single component or a few related components (child or sibling components).

• It is created using the appropriate React hooks inside a component.

• The local state is accessible only to the component where it was created unless passed down via props.

Example Use Case: Search Input Field

• The state managing a search term in a search bar remains local, as no other component needs access.

🔹 Global State

• Used when multiple components need access to the same state. It is stored at a higher level in the component tree. Global state can be managed using.

• React's Context API or state management libraries like Redux

  .

Example Use Case: Shopping Cart

• The shopping cart state must be accessible by multiple components (cart page, navbar, checkout page).

• Instead of lifting state up repeatedly, we store it in a global provider.

📌 Best Practice: Always start with local state and only use global state if multiple components require access to the same data.

3. When and Where to Create State

Step-by-Step Flow for State Creation

1. Do you need to store some data?

   • If NO, use a regular variable.

   • If YES, proceed to the next step.

2. Does this data change over time?

   • If NO, store it as a constant.

   • If YES, it needs to be stored in state.

3. Can the data be derived from existing state or props?

   • If YES, use the derived state(computed from the existing state).

   • If NO, create a new state variable.

4. Does the state need to trigger a re-render?

   • If NO, store it using a reference instead of state.

   • If YES, create state accordingly.

📌 Key Concept: Avoid storing unnecessary state—only create state if it cannot be computed from existing values.

4. Where to Place State in the Component Tree

1️⃣ State Belongs in the Component That Uses It

• If only one component needs the state, define it inside that component.

• Example: A modal’s isOpenstate should be stored inside the modal component.

2️⃣ If a Child Component Needs the State → Pass It Down as Props

• If a child component needs access to the state, pass it via props.

• Example: A counter where the parent component manages state and passes it down to the child component for display and interaction.

3️⃣ If Sibling or Parent Components Need the State → Lift It Up

• If multiple components need access to the same state, lift it to the first common parent. Example: A shared theme setting applied across multiple components.

📌 Key Concept: If multiple components need state, move it to their closest shared parent.

4️⃣ If Many Components Need the State → Use Global State

• If many unrelated components need access to the same state, store it in a global state management system like Context API or Redux.

• Example: User authentication state used across an entire application

5. Best Practices for State Management

• Always start with the local state before making it global.

• Keep state as close to where it’s used as possible.

• Only lift state up when necessary to avoid unnecessary re-renders.

• Use derived state whenever possible to avoid redundant state variables.

• Minimize unnecessary re-renders by structuring state efficiently.