Redux Interview Questions

Are you a novice, intermediate or advanced candidate preparing for a redux interview? First of all, congratulations on earning a slot among the shortlisted candidates. However, that’s not enough because you also want to clinch the job. What should you expect from the panelist? We have compiled some redux interview questions enough to assist you in convincing the employer that you are the match for the job.

Besides knowing the questions, you also need to answer them diligently. If that’s how you convince the interviewers that you have the skill set they are looking for, then you better rise to the occasion. These redux interview questions and their respective answers will let you do so. Check them out!

What is Redux?

It is an open-source library that Andrew Clark and Dan Abramov wrote using the JavaScript scripting language in 2015. It complements JavaScript libraries such as Angular and React to build responsive and user-friendly user interfaces (UIs). Its main role is to manage and centralize any application’s states and logic, whether running on a native, server, or client environment. It also simplifies testing, a crucial part of any application’s development. Redux is also suitable for unlocking state persistence, Redo or Undo and debugging. Additionally, it is compatible with various user interfaces and supports many add-ons.

What is Redux DevTools, and what are its main features?

Redux DevTools is a time travel environment that facilitates live editing in this library. It comprises a customized UI while coupling action replay and hot reloading. Its main features include the following;

• Thanks to the Redux DevTools, one can go back in time if they cancel related activities. It is also possible to check the action payload and all states.
• The persistState() store enhancer allows you to proceed with debug sessions across page reloads
• You can re-evaluate every stage action by updating the reducer’s code

Which are the basic principles of Redux?

Its basic principles include the following;

• There is only one source of truth: An application’s global state is stored in an object tree, usually inside a single store
• Read-only state: You need to emit an action to change an application’s state, usually an object explaining the happenings
• Changes occur through pure functions: Defining the transformation of a state tree and the respective actions requires writing pure reducers

What are the advantages of Redux?

Using redux translates to the following benefits;

• Predictable output: Redux applications have a store that’s the only source of truth. It eliminates any confusion arising from different parts of the app or syncing its current state with corresponding actions.
• Ease of testing: Most functions comprising redux code are small, pure, and isolated. These characteristics simplify the testing of such apps.
• Developer tools: It is important to track many things when developing applications. Redux developer tools simplify this process, thus allowing the developer to keep tabs on everything, state changes, and actions in real time.
• Great code organization: There is a certain way that one should organize redux code. Therefore, all developers end up with relatively similar code. Such consistency is suitable for a development team working on a certain application collectively.
• Server-side rendering: The initial render benefits from this advantage by forwarding stores created on the server to the client. The practice promotes search engine optimization (SEO) and improves user experience. That’s why Redux applications show great performance.
• Easy to maintain: Applications last for a long, and there is a need to maintain their code throughout. Thanks to the consistent structure and predictable output, expect it to be a breeze if you use redux.
• Substantive community: Redux community is already huge and also active. So, excellent contribution leads to a refine library that’s always growing for the better. Besides, you can also get ready-to-use apps amongst the community members.

What are the components of Redux?

They are three, namely;

• Reducer
• Action
• Store

What is a store in Redux?

The store is the single source of truth in redux applications. It puts together the actions, reducers, and states which are a crucial part of any application. Its responsibilities include;

• It stores the current application’s state from the inside
• The store also allows users to access the current state using store.getState()
• It allows one to update the state using the store.dispatch(action)
• It facilitates the registration of listener callbacks using the store.subscriber(listener)

Store methods include;

• replaceReducer(nextReducer)
• subscribe(listener)
• dispatch(action)
• getState()

What are the examples of frameworks compatible with Redux?

The most common one is React, which is most likely due to the common use of the pair by many developers. However, it also often works with many user interface layers as their data store. Besides React, other compatible frameworks are Vue, Angular, and Angular 2.

Which functional programming concepts structure redux?

They include;

• Treating functions like first-class objects
• It can control flow with arrays, recursions, and functions
• It is possible to link functions together
• No need to prioritize the order of code execution
• States don’t change
• It uses helper functions, including reduce and map filters
• It can also pass functions in arguments format

What is Flux?

It is an application design pattern similar to the Model View Controller design paradigm. This new architecture complements the Unidirectional Data Flow concept and React.

Are Redux and Flux different?

The answer to that question is affirmative, and the two are different in more than one way.

• Redux has one store for every application, whereas flux allows a single application to have more than one store
• Redux is an open-source library written in JavaScript, but flux is a design paradigm
• Developers use redux to create user interfaces and flux to create client-side web applications
• The business logic of a redux application is in a reducer, while that of s flux application is in a store

Highlight the features of a redux workflow.

They are four, and they are as follows

• Commit: Setting the current state right at the starting point
• Sweep: Deletion of any disabled action fired erroneously
• Revert: As the name suggests, it means reverting or rolling back to any state committed earlier
• Reset: It allows users to reset the state of a store

What are actions in redux?

They are JavaScript objects with a type field. Their role is to describe what has happened in the app. However, it doesn’t contain the details but highlights enough to explain what has happened.

What is a reducer in redux?

It is a pure function responsible for taking a previous state coupled with an action before it returns the next state.

What are the don’ts inside reducers?

There are things you shouldn’t do inside reducers to ensure that they remain pure such as;

• Modifying their arguments
• Performing certain side effects, including API calls and routing transitions
• Calling non-pure functions such as now() and Math.random().

What’s the role of constants in redux?

A constant helps a developer find the various uses of a particular functionality throughout a project when using an integrated development environment (IDE). Besides, it ensures that no typo translates to a bug later on by showing ReferenceError as soon as you make it. They come in handy in reducers and when creating actions.

Define a redux form

It works with redux and Reacts to allow a form in the latter to use the former to store its different states. A developer is at liberty to use it with typical user interface frameworks such as React Bootstrap, Material UI, and React Widgets. Alternatively, one can use it with simple HTML5 inputs.

Redux Form has several primary features. Name them.

• Field values persistence thanks to the redux store
• Validating either sync or async and submission
• Field values’ formatting, parsing as well as normalization

What would you do to access a redux store outside a react component?

Use the createStore function to export this store from its current module. As you do so, it is important not to pollute the global window object. The code is as simple as;

store = createStore(myReducer);

export default store;

What is a redux saga?

Redux saga is a library focusing on managing any side effect in a redux application. Common side effects include the interaction with your browser’s history, access to the browser’s local storage, and the creation of network requests. The library allows you to write a side effect as a saga while separating them from their counterparts, reducers. Consequently, you get a modular code that’s easy to test.

Do you have to use redux-saga in ReactJS applications?

No, it is not mandatory to use redux-saga in ReactJS applications. However, if you want to manage side effect logic which is usually complex, redux saga can be a lifesaver.

How does React Context differ from React Redux?

By design, using React Redux in an application requires you to code it first before merging the separate code into your main project. On the other hand, it is possible to use React Context in your application directly. It is also important to note that React Redux provides more features than React Context.

Explain the structure of redux top-level directories

These examples show how redux structures various directories

• Store: It is a directory suitable for medium and small apps used to initialize a store
• Reducers: The directory is used for the application’s reducers, and the name corresponds to the state key
• Actions: This one is for its action creators, and its file name corresponds to the app’s part
• Containers: This directory contains React components connected to redux and is usually called “smart.”
• Components: This directory contains React components strange to redux and are usually called “dumb.”

How can you differentiate mapStateToProps() from mapDispatchToProps()

As much as the two are methods, they differ in various ways. For instance, mapStateToProps render stored data, whereas mapDispatchToProps render action creators using props to the component. The mapStateToProps() results in a plain object, but you can call an action creator directly due to the dispatcher call wrap in the mapDispatchToProps() method.

That said and done, you merge these results into the prop of the component regardless of the method used. Last, mapStateToProps() connects the redux state to the react component’s props, while mapDispatchToProps() connects redux actions to the react props.

Do you have any idea about Redux Toolkit?

Yes, since it is hard to go unnoticed. It makes developers’ lives easy and saves them a lot of time. It contains common redux add-ons such as Reselect and Redux Thunk. Developers use the former to write selector functions and the latter for asynchronous logic.

What do you understand from the term Redux Thunk?

It is a middleware that allows one to write an action creator. However, instead of returning an action, it returns a function. It is suitable for delaying an action’s dispatch or allowing it only after meeting a particular condition. The parameters received by the inner function are store methods getState() and dispatch.

How can you add middleware to redux?

It involves using applyMiddleware and then passing every middleware as a different argument.

Is it necessary to keep all the component states in the redux store?

No, that’s unnecessary and good for ensuring that your application remains as small as possible. However, do not hesitate to keep those that simplify using DevTools or make any other difference to you as a programmer.

Tell us about Redux in ReactJS

First of all, it is redux’s official binding with React. The design ensures that React components can read data available in the redux store. It also instructs actions to the redux store for data updates. Its goal is to simplify app scaling by providing a state management method through the unidirectional data flow.

What’s the lifecycle of an application made with React and redux?

The data flow begins from the UI component, where a call back emanates, dispatching an action and a payload. Next, reducers generate a new app state after intercepting and receiving those dispatched actions. Finally, the components’ hierarchy facilitates the propagation of the actions from the redux store.

Is Redux different from Relay?

Yes, because redux doesn’t deal with data fetching unless done manually. On the other hand, Relay has what it takes by design to cache and optimize data. Redux takes care of all the application’s states, whereas Relay only takes care of the server’s state.