Evaluating Remote Tech Candidates

Best Redux Interview Questions in 2022

Gabriela Molina
- 3 min. to read

Identifying the best Redux developers depends on how good your recruitment and interviewing processes are. We created a guide with the best Redux interview questions in 2022 that will not only help you choose the candidates with the best expertise and knowledge but also those who will successfully adapt to your company.

What is Redux Used For?

Redux is an open-source JavaScript library created by Dan Abramov and Andrew Clark in 2015. The main purpose of this library is to manage the application state. It’s primarily used with React or Angular libraries to build user interfaces (UI).

As explained above, Redux is a small library with a limited API designed to be a predictable container for the application state. In contrast to other libraries, Redux is not used for everything; It requires developers to have specific knowledge and skills because it is not a traditional library.

These are some of the reasons why to use Redux:

  • Developers can predict the outcome. With only one source of truth present (the store), there are almost no challenges in syncing the current state with actions and other aspects of an application.
  • It’s maintainable. Redux is strict in code organization, making the outcome predictable and the code easier to maintain.
  • It’s easier than other libraries to test. When developers code in Redux, it involves isolated functions, making testing or identifying possible mistakes/errors easier.

11 Best Redux Interview Questions (Answered)

These are the 11 most frequently asked Redux interview questions:

1. Explain what ‘actions’ are in Redux

Simply put, actions are events. Actions work by sending data from user interaction, API calls, or other internal events, and form submission, to the store. These are the only possible source of information for the store. You send them to the store with the method store. dispach().

Redux documentation gives a simple example of an action that represents adding a new todo item:

Const ADD_TODO = ‘ADD_TODO’

{

type: ADD_TODO,

text: ‘Build my first Redux app’

}

All actions are plain JavaScript objects and need to have a type property. This property should indicate the type of action being performed. 
Here´s another example where you can also show a function and a call to action:

{

type: LOGIN_FORM_SUBMIT,

payload: {username: ‘alex’, password: ‘123456’}

}

Actions are just created with ‘action creators,’ which are simply functions that return the actions.

function authUser(form) {

return {

type: LOGIN_FORM_SUBMIT,

payload: form

}

}

Then, to call the action somewhere in the app, you simply use the dispatch method:

dispatch(authUser(form));

2. What are ‘reducers’ used for in Redux?

Reducers specify how the application’s state changes in response to actions. It is a pure function that takes the previous state and an action, transforming it into the next state. 

Here’s an example of storing the currently selected visibility filter and the actual list of todos for a todo app:

{

visibilityFilter: ‘SHOW_ALL’,

todos: [

{
text: ‘Consider using Redux’,

Completed: true,

},

{

text: ‘Keep all state in a single tree’,

completed: false

}

]

}

3. Tell me the responsibility of the Store in Redux and give an example of how to create it

The Store brings the reducers and actions together. It accomplishes the following tasks, as noted in the Redux documentation:

  • Holds application state
  • Allows access to state via getState()
  • Allows state to be updated via dispatch(action)
  • Registers listeners via subscribe(listener)
  • Handles unregistering of listeners via the function returned by subscribe(listener)

Here’s an example of how to create a store importing and then passing the previous example of combineReducers():

import {createStore} from ‘redux’

import todoApp from ‘./reducers’

let store = createStore(todoApp)

Another way to accomplish this is by specifying “the initial state as the second argument to createStore(). This is useful for hydrating the state of the client to match the state of a Redux application running on the server.”

let store = createStore(todoApp, window.STATE_FROM_SERVER)

 4. How can we use connect from React Redux?

To use connect from React Redux, we need to follow certain steps to use our store in our  container: 

  1. Use the mapStateToProps(): This would map the state variables from our store to the props which we specify.
  2. Connect the above props to our container: The object returned by the mapStateToProps component is connected to the container.

Here´s an example:

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: state.data };
}

export default connect(mapStateToProps)(App);

5. How can you add multiple middlewares to Redux? 

For adding multiple middlewares to Redux, we can use applyMiddleware. You can pass each piece of middleware as the new or another argument, depending on your preferences. The purpose is to pass every single piece of middleware. 

Here´s an example: 

import { createStore, applyMiddleware } from 'redux'

const createStoreWithMiddleware = applyMiddleware(ReduxThunk, logger)(createStore);

6. What are the differences between mapStateToProps() and mapDispatchToProps()?

mapStateToProps() is a function used to provide the store data to your component. On the other hand, mapDispatchToProps() is used to provide the action creators as props to your component.

According to the documentation, if mapStateToProps() argument is specified, the new component will subscribe to Redux updates. So, anytime the store is updated mapStateToProps() will be called. And with mapDispatchToProps every action creator wrapped into a dispatch call so they may be invoked directly, will be merged into the component’s props.

Here´s an example: 

function mapStateToProps(state) { 
return { todos: state.todos }
} function mapDispatchToProps(dispatch) 
{ return { addTodo: bindActionCreators(addTodo, dispatch) } 
}
 export default connect(mapStateToProps, mapDispatchToProps)(Todos);

7. How do you select the initial state in Redux? 

To select the initial state in Redux, you need to exceed the initial state as a second dispute to “create store.”

Here´s an example:

const rootReducer = combineReducers({
  todos: todos,
  visibilityFilter: visibilityFilter
});

 
const initialState = {
  todos: [{id:123, name:'sudheer', completed: false}]
};

const store = createStore(
  rootReducer,
  initialState
);

8. What is the main difference between React Redux and React Context?

To use React-Redux in an application, you need to code it separately and then merge them. Redux is more powerful than React Context and it provides numerous features. React Context can be used directly in the application, and it’s best for passing the data to the deploy component nested components. However, it doesn’t include a great number of features. 

9. What is the purpose of the constants in Redux?

With constants, you can easily find all usages for that specific functionality across the project when you use an IDE. Constants also prevent you from introducing errors caused by typos (In such cases you’ll get a ReferenceError notification).

Normally we save constants in a single file (constants.js or action Types.js). Here’s an example: 


export const ADD_TODO = 'ADD_TODO';
export const DELETE_TODO = 'DELETE_TODO';
export const EDIT_TODO = 'EDIT_TODO';
export const COMPLETE_TODO = 'COMPLETE_TODO';
export const COMPLETE_ALL = 'COMPLETE_ALL';
export const CLEAR_COMPLETED = 'CLEAR_COMPLETED';

You can use them during actions creation (actions.js):

import { ADD_TODO } from './actionTypes';

export function addTodo(text) {
  return { type: ADD_TODO, text };
}

Or in reducers (reducer.js): 

import { ADD_TODO } from './actionTypes';

export default (state = [], action) => {
  switch (action.type) {
    case ADD_TODO:
      return [
        ...state,
        {
          text: action.text,
          completed: false
        }
      ];
    default:
      return state
  }
};

10. Explain what are Redux forms and its major features

Redux forms help to enable a form in React to use Redux for storing all of its states. They can be used with raw inputs in HTML5.

Its major features are:

  • Field values persistence through the Redux store
  • Validation and submission
  • Formating, parsing, and normalization of field values. 

11. How can you structure the top-level directories in Redux?

Redux applications have different top-level directories, such as: 

  • Components: Used for dumb components unfamiliar with Redux.
  • Containers: Used for smart components connected to Redux.
  • Actions: Used for all the action creators; the file name corresponds to the part of the app.
  • Reducers: Used for all the reducers; the file name corresponds to the state key.
  • Store: Stores are used for store initialization – this structure works best for small and medium-size applications. 

React Redux Interview Questions For Experienced

If you´re looking for experienced developers, these are common questions that we usually ask senior Redux developers:

  1. How to make Ajax request in Redux?
  2. What’s the purpose of at (@) symbol in the redux connect decorator?
  3. What are the differences between call and put in redux-saga?
  4. What are the similarities between Redux and RxJS?
  5. Explain how Relay is different from Redux?
  6. What is Redux DevTools? 
  7. What are the downsides of Redux over Flux?
  8. How to reset state in redux?
  9. What is the mental model of redux-saga?

Redux Interview Questions for Remote Candidates

One thing is hiring a developer, a completely different thing is hiring a remote one. 

If you’re interested in accessing a wider global pool of talent while lowering your costs, these are some of the best remote interview questions that will help you identify which candidates are great remote Redux developers: 

  • Have you worked remotely? If you have, what did you like the most, and what did you dislike? 
  • What are the best ways to perform remote code reviews?
  • How do you deal with the challenges of working with remote development teams?
  • What are your favorite working hours?
  • How do you schedule your workday? 
  • Tell me about a time you had a misunderstanding/conflict with remote coworker. How did you handle it?
  • Who´s the most difficult person you ever worked with, and why?
  • What do you do when you get stuck with a task?
  • What are your favorite tools/workflows to ensure quality control?

Choose the Right Redux Developer with DistantJob

As a remote recruitment agency with more than 10 years of experience, we know that great candidates are more than skills and experience. We´ve helped companies hire remote developers who, besides being fluent in English and living in time zone-friendly areas, also make the perfect match for their company´s culture. Hire developers remotely with DistantJob Today!

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