Explain the flow of data in React-Redux

💡 Concept Name

React-Redux Data Flow describes how data moves in a React application using Redux for predictable state management with a unidirectional flow.

📘 Quick Intro

In React-Redux, data flows in one direction: from the Redux store to React components and back via dispatched actions. This ensures predictable state updates and easy debugging.

🧠 Analogy / Short Story

Imagine a post office system where you send letters (actions) to a central sorting center (store). The sorting center updates the mailboxes (state) and notifies houses (components) to update their information. You can only send letters through official mail (dispatch actions) ensuring everyone gets the right info in an orderly way.

🔧 Technical Explanation

📦 The store holds the entire application state.
📢 Components dispatch actions to signal changes.
⚙️ Reducers receive actions and return a new state based on the action type.
🔄 The store updates state and notifies subscribed components.
🧩 React components read state from the store via connect() or useSelector().

💻 Real Code Example


// action.js
export const increment = () => ({ type: 'INCREMENT' });

// reducer.js
const initialState = { count: 0 };
export function counterReducer(state = initialState, action) {
  switch(action.type) {
    case 'INCREMENT':
      return { count: state.count + 1 };
    default:
      return state;
  }
}

// store.js
import { createStore } from 'redux';
import { counterReducer } from './reducer';
export const store = createStore(counterReducer);

// Counter.js
import React from 'react';
import { useSelector, useDispatch } from 'react-redux';
import { increment } from './action';

function Counter() {
  const count = useSelector(state => state.count);
  const dispatch = useDispatch();

  return (
    <div>
      <p>Count: {count}</p>
      <button onClick={() => dispatch(increment())}>Increment</button>
    </div>
  );
}

❓ Interview Q&A

Q1: What is the Redux store?
A: The store holds the entire state of the application in one place.

Q2: How do components update the state?
A: By dispatching actions to the store.

Q3: What role do reducers play?
A: Reducers handle actions and return a new state.

Q4: What does dispatching an action mean?
A: It sends an object describing a change to the store.

Q5: How do components access the Redux state?
A: Using connect() or useSelector() hook.

Q6: Is Redux synchronous or asynchronous?
A: Redux core is synchronous but middleware like thunk can handle async operations.

Q7: Can Redux be used without React?
A: Yes, Redux is a standalone library for state management.

Q8: What is the benefit of unidirectional data flow?
A: It makes the app predictable and easier to debug.

Q9: How does React know to re-render components?
A: When the store state changes and components subscribe to updates.

Q10: Can you have multiple reducers?
A: Yes, combined using combineReducers().

📝 MCQs

Q1. What holds the entire Redux state?

Reducer
Store
Action
Dispatch

Q2. How do you update Redux state?

Changing state directly
Dispatching actions
Using useState
Calling setState

Q3. What does a reducer do?

Updates UI
Returns new state
Dispatches actions
Creates store

Q4. What is dispatch in Redux?

Updates state
Sends action to store
Calls reducer
Subscribes components

Q5. How do React components access Redux state?

Props
useState
useSelector or connect
Context API

Q6. Is Redux synchronous?

Always async
Core is synchronous
Never async
Depends on React

Q7. Can Redux be used without React?

No
Yes
Only with React
Only with Angular

Q8. What benefit does unidirectional flow provide?

Performance
Predictability
Complexity
Flexibility

Q9. How does React know when to re-render?

User input
Store state changes
Timer
Component load

Q10. Can you combine multiple reducers?

No
Yes
Sometimes
Only one allowed

💡 Bonus Insight

Middleware like Redux Thunk or Saga extends Redux to handle asynchronous actions, making the data flow more flexible for real-world applications.

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