Redux Interview Questions

Dive into the world of state management with 'Redux Interview Questions.' This blog is your ultimate resource for preparing for Redux-related interviews, featuring a comprehensive collection of questions and detailed answers. Whether you're a front-end developer, a React enthusiast, or a Redux user, our guide covers Redux fundamentals, actions, reducers, and best practices. Prepare with confidence and explore the power of Redux in managing state and data flow in your web applications.

1. What is Redux?

Redux is a predictable state container for JavaScript applications. It helps manage the state of an application in a predictable way by enforcing a unidirectional data flow pattern.

2. Explain the core principles of Redux.

Redux is based on three core principles: single source of truth, state is read-only, and changes are made with pure functions. The single state tree makes it easier to debug and understand the application's state.

3. Difference between Redux and Flux.

The main differences in the comparison: Redux vs Flux are as follows:

Number of stores per application Redux includes a single Store per application. Rather than placing state information in multiple Stores across the app, Redux keeps everything in one region of the application Flux includes multiple Stores per application.
Architecture Redux is an open-source JavaScript library used for creating User Interfaces. Flux\'s architecture is designed to build client-side web apps.
Place where Business Logic of the Application Resides In Redux, the business logic of the application resides in the Reducer. In Flux, the business logic of the application resides in the Store.

4. What is Redux in React js?

Redux in React is the official React binding for Redux which allows the components in React to read data from a Redux Store, and dispatch Actions to the Store for updating the data. The purpose of Redux is to help applications scale well by providing means to manage the state via a unidirectional data flow model. 

5. State the core principles of Redux.

The core principles of Redux are as follows:

6. What are the advantages of using Redux?

Some of the advantages of using Redux are as follows:

7. Is it true that Redux can only be used with React?

No, it is not true that Redux can only be used with React. Redux is being used as a data store for lots of UI layers. There are bindings available in Redux for React, Angular, Angular 2, Vue, etc. 

8. What do you understand about Redux Toolkit?

Redux Toolkit is Redux\'s official, opinionated, batteries included toolset for efficient Redux development. It also consists of the most widely used Redux add-ons, for instance, Redux Thunk for asynchronous logic,  Reselect for writing selector functions and many more for making development easy for developers and saving them time.

9. What are some of the major features of Redux DevTools?

Some of the major features of Redux DevTools are as follows:

10. Is it necessary to keep all the component states in the Redux store?

No, it is not necessary to keep all the component states in the Redux store. We have to keep your application state as small as possible and therefore, we should do it only if it makes a difference for us to keep something there or maybe if it makes the use of Dev Tools easier.

11. Highlight the key differences between mapStateToProps() and mapDispatchToProps()?

The key differences between mapStateToProps() and mapDispatchToProps() are given below:

mapStateToProps() mapDispatchToProps()
The mapStateToProps() method is used to render the stored data to the component. The mapDispatchToProps() method is used to render the action creators with props to the component.
The entirety of the results of the mapStateToProps() method is a plain object which is later merged into the component’s prop. In the mapDispatchToProps() method, each action creator is wrapped in the dispatcher call so that they can be called upon directly and later merged into the component’s prop.
This method\'s use is to connect the redux state to the props of the react component. This method\'s use is to connect redux actions to the react props.

12. What do you understand by an action in Redux\'s architecture?

In the Redux architecture, actions are nothing but the plain JavaScript objects which contain a type field. They can be thought of as an event that is used to describe something which has happened in the application. Actions contain only a tiny bit of information that is required to mention what has happened.

13. Give an example of the usage of Actions in Redux\'s architecture.

An example of the usage of Actions in Redux\'s architecture is given below:

const addingTodoAction = {     type: \'ADD\',     payload: \'Do-homework\'}

14. Where can we use Redux?

Redux is primarily being used along with React. However, we can also use it along with Angular, Vue, Meteor, etc. using the bindings it has to offer to us.

15. What are constants in Redux?

Constants in Redux help us in easily finding all the usages of a particular functionality across our entire project when we are using an Integrated Development Environment (IDE). Using constants, we can avoid silly bugs caused because of typing errors or typos as it shows a "ReferenceError" whenever a typo is made.

16. Show using code how constants can be used in Redux.

First of all, we can store all the constants in a single file in our project named constants.js or something else as follows:


After storing the constants in one place, we can use them in two ways in our project:

 import { DELETING_TODO } from \'./constants\';export function deletingTodo(text) {  return { type: DELETING_TODO, text };}
 import { EDITING_TODO } from \'./constants\';export default (state = [], action) => {  switch (action.type) {    case EDITING_TODO:      return [        ...state,        {          text: action.text,          completed: false        }      ];    default:      return state  }};

17. What are reducers in Redux\'s architecture?

Reducers in Redux\'s architecture are pure functions that are used to take the previous state and an action and return the next state. Its syntax is given below:

 (previous_state, action) => new_state

18. Show with an example how reducers are used in Redux.

An example of how reducers are used in Redux is given below:

const initial_state = { value: 0 }function countReducer(state = initial_state, action) { // Checking to see if the reducer cares about this action if (action.type === \'counter/incremented\') {   // If the action is of type "counter" or "incremented", we make a copy of `state`   return {     ...state,     // We also update the copy with the new value     value: state.value + 1   } } // If not, we return the original state unchanged return state}

19. What is the mental model of redux saga?

Redux Saga functions as a separate thread in our programme which is solely responsible for side effects. Redux Saga is a redux middleware. In other words, it means that it can be started, paused, and aborted from the main application using standard Redux actions, has access to the entire Redux application state, and can also dispatch Redux actions.

20. Describe what is meant by a "store" in Redux.

“Store” in Redux is used to carry together all the states, reducers, and actions which create the app. Some of the responsibilities of the store are as follows:

21. Name all the Redux Store methods.

All the Redux Store Methods are as follows:

22. Give an example depicting the usage of a Redux store.

An example depicting the usage of a Redux store is given below:

 import { createStore } from \'redux\'const store = createStore(todos, [\'Use Redux\'])function deletingTodo(text) { return {   type: \'DELETING_TODO\',   text }}store.dispatch(deletingTodo(\'Do the homework\'))store.dispatch(deletingTodo(\'Buy coffee\'))

23. Explain with an example how to set the initial state in Redux.

In order to set the initial state in Redux, we have to pass the initial state as the second argument to createStore as shown below:

 const rootReducer = combineReducers({  todos: todos,  visibilityFilter: visibilityFilter});const initialState = {  todos: [{id:100, name:\'ritik\', completed: true}]};const store = createStore(  rootReducer,  initialState);

24. What do you understand about Redux Thunk?

Using Redux Thunk middleware, we can write action creators returning a function instead of an action. This thunk can postpone the dispatch of an action, or do conditional dispatchment. The arguments passed to the inner function are the store methods dispatch and getState(). In the event of an action creator returning a function, the function gets executed by the Redux Thunk middleware and it does not have to be pure. In other words, the function is allowed to have side effects, including executing asynchronous API calls. It can even dispatch actions. Redux thunk is used to delay the dispatch of an action, or to dispatch in the event of a certain condition being met. At the time of dispatch of a function instead of an action object, if Redux Thunk middleware is enabled, the middleware will call that function with the dispatch method itself as the first argument.

25. What are the workflow features in Redux?

The workflow features in Redux are as follows:

26. Differentiate between Relay and Redux.

The key differences between Relay and Redux are given below:

Relay Redux
The state originating from the server is taken care of by Relay. All the states of the application are taken care of by Redux.
Relay can be used for caching and optimizing the data. Redux is not responsible for handling data fetching (it can be done manually though).

27. How can we use connect from react redux?

In order to use connect from React Redux, we will have to follow a couple of steps to use our store in our container:

A sample code for connect from react-redux is given below:

import React from \'react\';import { connect } from \'react-redux\'; class App extends React.Component {   render() {     return <div>{this.props.containerData}</div>;   } } function mapStateToProps(state) {   return { containerData: state.appData }; } export default connect(mapStateToProps)(App);function mapStateToProps(state) {  return { containerData: };}export default connect(mapStateToProps)(App);

28. What are Redux forms? What are its major features?

Redux Forms present in React and Redux help in enabling a form in React to use Redux for storing all of its states. They can be used with raw inputs in HTML5. Redux forms work extremely well with User Interface (UI) frameworks, for instance, Material UI, React Widgets, React Bootstrap and many more.

The major features of Redux forms are as follows:

29. How can we access a redux store outside a react component?

For accessing a redux store outside a react component, we can export the store from the module where it has been created with createStore as done in the following example:

store = createStore(reducer);export default store;

30. Differentiate between React Redux and React\'s Context API.

The key differences in the comparison: Context Api vs Redux are as follows:

React Redux React Context API
In order to use React-Redux in our application, we need to code it separately and then merge it into the main project. React Context can be used in the application directly.
The number of features provided by React-Redux is comparatively more than React Context. The number of features provided by React Context is comparatively less than React-Redux.

31. What do you understand about the Redux Saga?

Redux Saga is a middleware library that can be useful for allowing a Redux store to interact with the resources outside of itself in an asynchronous manner, for example, making HTTP requests to external services, accessing browser storage, executing Input/Output operations and many more. These operations are also called side effects.

32. What are the things which we should never do inside a reducer?

The things which we should never do inside a reducer are as follows:

33. Code Snippet: Redux Store Configuration

import { createStore } from 'redux';
import rootReducer from './reducers';

const store = createStore(rootReducer);

34. Online Resources: