1. What is Redux?

Answer: Redux is a predictable state management library for JavaScript apps, commonly used with React. It stores the entire application state in a single JavaScript object called the store. Components read from the store and dispatch actions to update it.

2. What are the core principles of Redux?

Answer:

1. Single Source of Truth: State is stored in a single object.
2. State is Read-Only: You can’t directly modify state—only through actions.
3. Pure Functions: Reducers are pure functions that return new state based on action.

3. What is a store in Redux?

Answer: The store holds the entire app state and provides methods to access (getState()), update (dispatch()), and listen (subscribe()) to state changes.

import { createStore } from "redux";
const store = createStore(reducer);

4. What is an action in Redux?

Answer: An action is a plain JS object that has a type field and optionally a payload. It describes what happened, not how the state should change.

{ type: 'INCREMENT', payload: 1 }

5. What is a reducer?

Answer: A reducer is a pure function that takes the previous state and an action, then returns the new state. It must be pure (no side effects).

function counter(state = 0, action) {
  if (action.type === "INCREMENT") return state + 1;
  return state;
}

6. How do you update state in Redux?

Answer: By dispatching an action to the store. The reducer handles the action and returns a new state.

store.dispatch({ type: "INCREMENT" });

7. What is combineReducers?

Answer: Redux allows splitting reducers into smaller functions and combining them with combineReducers. Each reducer manages its own slice of state.

import { combineReducers } from "redux";
const rootReducer = combineReducers({ auth: authReducer, user: userReducer });

8. What is dispatch() in Redux?

Answer: dispatch() sends an action to the reducer to update the state. It’s the only way to trigger a state change in Redux.

store.dispatch({ type: "LOGIN_SUCCESS" });

9. How do you access state in Redux?

Answer: Use store.getState() or in React use useSelector() hook.

const counter = useSelector((state) => state.counter);

10. What is middleware in Redux?

Answer: Middleware intercepts dispatched actions before they reach reducers. Useful for logging, async operations, or modifying actions. Example: redux-thunk, redux-logger.