Top 50 React Interview Questions and Answers in 2022

16-Aug-2022

Knowing how much effort it takes to ace these interviews, we have created this list of the best React Interview questions that have the highest likelihood of appearing. You will have the best chance of completely responding to the majority of the questions presented in a React.js interview if you go over these top queries.

It's getting harder to choose the best technology while creating a website or application. React is regarded as the Javascript framework with the fastest growth rate out of everyone. The market for JavaScript tools is constantly gaining ground, and the need for React certification is rising exponentially. React is unquestionably a success for front-end developers all over the world thanks to its short learning curve, reusable components, and clean abstraction. Therefore, this blog on the best React Interview Questions is for you if you're an aspiring front-end developer and are getting ready for interviews. The following React interview question requires you to consider some of the key features that React provides.

Best React Interview Questions for your successful attempt

1. How is Real DOM distinct from Virtual DOM?

We may find the distinction between Real and Virtual DOM in the following points:

In a virtual DOM, one can make changes easily while with a Real DOM changes are expensive. 

Real DOM demands more memory and there occurs higher wastage while there is only minimal wastage of memory with virtual ROM.

In real DOM upon updating an element, a new DOM gets created. While with Virtual DOM, A JSX element gets updated if the element exists. 

Real DOM is capable of manipulating HTML directly while Virtual DOM cannot even update. 

Virtual DOM facilitates faster updates while updates are slow with Real DOM. 

2. Define React

A popular JavaScript library called React was introduced in 2011. It was developed by Facebook developers, and its main application is frontend development. React employs the component-based method, which guarantees to assist you in creating components with a high degree of reusability. For creating and designing intricate mobile user interfaces and web applications, React is well known.

3. What does the term "Virtual DOM" mean?

A straightforward JavaScript object that is a perfect replica of the matching real DOM is known as a virtual DOM. A node tree is made up of elements, those elements' attributes, and other aspects can be thought of as this. It builds a node tree using React's render function and updates it in response to changes made to the data model. Typically, people or system actions that result in these changes are what cause them.

4. What are some of React's key characteristics?

React offers a variety of features that are each used for a particular function. 

The following are the significant ones:

A single-direction data flow concept is used by React.

It handles all aspects of server-side data management and processing.

React makes use of the Virtual DOM, which has several benefits of its own.

5. What does the term "JSX" mean?

The acronym for JavaScript XML is JSX. It is a file that React uses to extract the JavaScript essence and utilize it to its full potential. Even bringing forth HTML and JavaScript's simple syntax is included. Because of the great readability of the generated HTML file, this ensures that the application will run more quickly.

6. Can a JSX file be read by browsers?

No, JSX files cannot be read directly by browsers. It can only read objects that JavaScript provides. Now, a JSX file needs to be converted using JSX transformers into a JavaScript object before it can be loaded into the browser and used in the pipeline.

7. What causes the popularity of React?

When developing an application, React offers users a plethora of benefits. Here are a few of them:

• UI testing is made simple with React.
• React is simple to connect with various frameworks, like Angular.
• The high readability index guarantees simple comprehension.
• Both client-side and server-side requirements can be met with React.
• It improves overall effectiveness and application performance.

8. Are there any drawbacks to React?

The following list of setbacks that occur while using React:

• Because JSX and inline template formatting are used, writing the code is challenging.
• Beginners may struggle to understand its syntaxes and approaches.
• A potentially overwhelming amount of information is available in the library.
• React requires dependencies because it is just a basic library and not a full-fledged framework.

9. What does React's component-based architecture actually mean?

Components in React serve as the building blocks for creating application user interfaces. All of the constituent entities become entirely reusable and independent of one another once the component-based system is in place. This indicates that rendering the application is simple and independent of other UI elements. 

10. Explain briefly the functioning of Rendering in React?

Since every component in React must be rendered, rendering is a key component. The render method is employed to perform this. A DOM component-representing element is returned by the method once it has been called. Additionally, by enclosing the HTML tags and running them through the render method, many HTML elements can be rendered at once. 

11. Define States in React?

One of the key components of React is state formation. It is regarded as a source of information or an object that regulated functions like component behavior and rendering. States are a simple way to construct dynamic and interactive components in React.

12. What do React props do?

In React, properties are referred to as "props." Props are immutable components that can only be read. Props adhere to a hierarchy in an application that is transmitted from parent components to child components. The opposite is not supported, though. This is done to make sure that there is always only one direction in which data can flow.

13. Explain the purpose of the Arrow function in React?

In React, an expression is written using an arrow function. It makes it simple for users to manually bind components. When working with higher-order functions, in particular, the functionality of arrow functions can be very helpful.

14. What in React is a higher-order component?

In React, higher-order components (HOCs) are a frequently used technique for implementing ideas involving the logic of component reusability. They enable users to reuse the code and bootstrap abstraction quickly while not being a native component of the React API. HOCs are also utilized to make it easy to share behaviors across all of React's components, further improving the application's functionality and effectiveness.

15. What does React's create-react-app command mean?

React has a straightforward command-line interface (CLI) called create-react app to construct applications with no build setup. When utilizing the CLI, all tools are already configured, allowing users to construct applications by concentrating more on the code and less on dependencies.

16. Mention a few of the benefits of utilizing React's create-react app?

By using create-react-app, one reaps the following benefits:

• Support for floe statements, JSX and ES6
• Produced and Available auto-prefixed CSS
• Quick Interactive testing elements 
• Debugging live development servers for JSS, CSS, and other file handling scripts

17. What does the term "Redux" mean?

The state of the application is kept in a single entity using Redux. Typically, this straightforward thing is a JavaScript object. By pushing out actions from the application and creating associated objects for them that are utilized to modify the states, it is possible to change states.

React Interview Questions and Answers for Intermediate Level

18. What are the three stages in the React component life cycle?

The three stages of a component life cycle are as follows:

Initial rendering: This stage marks the beginning of the component's trip toward the DOM.

Update: After being added to the DOM, the component can be modified and rendered once more if necessary.

Unmounting: The component is eventually removed from the DOM after it has been destroyed.

19. What do React events entail?

Events are triggered by any actions that are taken in React, such as moving the mouse or pushing a keyboard key. Events then respond to these triggers by carrying out predetermined actions. React's event handling is extremely similar to the DOM architectures.

20. What distinguishes React's routing from traditional routing?

The following aspects can be used to demonstrate how conventional routing and routing in React are distinct from each other:

Pages: In traditional routing, each view is treated as a separate file, however in React, each view is treated as a single HTML item.

Navigation: Traditional routing requires users to go between websites in order to view content. As objects are re-issued to build new views in React, the views are not refreshed.

21. Can React and AJAX be combined?

Yes, React can be used with any AJAX library, including Axios and jQuery AJAX, with ease. Maintaining the states of the components is one vital thing, and in this case, the props are handed from the parents to the child components. Even now, the inability of child components to return props to their parents significantly improves rendering efficiency when dynamic data is taken into account.

22. What do React's "synthetic events" mean?

React uses synthetic events, which are objects that serve as cross-browser wrappers for native events. This is done to guarantee that the API can be used by a range of browsers and that the event contains all properties.

23. What do React's stateful components do?

Entities that store changes and store them in memory are known as stateful components. Changes to the state can be made here, and information on past, present and future changes can also be stored.

24. What do React refs do?

In React, references are abbreviated as "Refs." Refs are used to keeping track of a reference to a certain React component or element. Later, using the render function, this is returned. They are primarily employed in the subsequent situations:

• To start Pressing animations
• To Integrate External DOM libraries
• Control focus and implement media playback

25. What do React's controlled components do?

In React, components that can preserve their state are referred to as controlled components. The parent component has complete control over the data, and props are used to obtain the most recent value. When employing callbacks, this is done to alert about each change that happens.

26. Why does React need a router?

In React, a router is absolutely necessary because it controls numerous routes whenever a user fills in a URL. The user is directed to the specific route if it is available for the matching URL in the router.

27. What elements makeup Redux in React?

Redux is made up of the following four parts:

The object that indicates the call in action

Reducer: The state change repository

Store: the object tree and state storage

View: Shows information supplied by the store

28. What are the drawbacks of utilizing MVC with React?

Using MVC in React has a tonne of benefits, but there are a few minor drawbacks, as listed below:

• Memory waste is prevalent.
• Manipulation of DOM is expensive.
• The program becomes sluggish.
• There are many dependencies established.
• Models become more intricate.

29. What applications involve higher-order components (HOCs)?

HOCs are employed for a number of tasks, including:

• Manipulating the settings
• Modification of the state and abstraction
• Make a hijacking.
• Reusing Bootstrap abstraction in code

30. Explain Pure Components in React?

In React, pure components are single-element objects. 

They can take the place of a component that just has the render() function and are quick and easy to develop. This is done to guarantee that the application performs well and that the code is kept straightforward at the same time.

31. Identify the distinction between React's Controlled and Uncontrolled components.

As the name implies, a controlled component is one that React has total control over. It serves as the only source of information for the forms. A component is considered uncontrolled if the DOM, rather than the React component, handles the form data. React's refs are typically used for this.

32. How do you instruct React to build in production mode? 

By setting the process.env.NODE ENV variable to production, React may be programmed to build directly into production.

33. What purpose do keys provide in React?

Unique Virtual DOM Elements along with their related data driving the UI are identified by keys. By recycling all of the already present items in the DOM, they aid React in rendering optimization. These keys, which React uses to simply reorder the elements rather than re-rendering them, must be a distinct number or string. Consequently, the performance of the application improves as a result.

34. Describe Flux?

The unidirectional data flow is enforced by the architectural pattern known as flux. Using a central Store with authority over all data, it manages derived data and facilitates communication between various components. The only place where data can be updated across the entire application is here. Flux gives the program stability and lowers run-time errors.

35. What three guiding principles does Redux adhere to?

• Only reliable source: An object/state tree within a single store contains the state of the entire application. The single state tree makes it simpler to debug or examine the application and keep track of changes over time.
• A read-only state: Only initiating action can change the status. A simple JS object that describes a change is called an action. The action is the minimal representation of the change to the data, just as the state is the minimal representation of the data.
• Pure functions are used to specify changes: Pure functions are required to specify how the state tree is altered by operations. Pure functions are ones whose output is solely determined by the values of their input parameters.

36. Explain One-Source-Of-truth?

Redux uses "Store" to keep track of all of the application's state in one location. As a result, the Store has all of the component's state information, and the Store itself provides updates. The single state tree makes it simpler to debug or examine the application and keep track of changes over time.

37. List the Redux's components.

These are the following parts of Redux:

• Action: A descriptive term for what transpired.
• Reducer: Here, it is decided how the state will alter.
• The complete application's state and object tree are preserved in the store.
• View - Simply shows the information supplied by the Store.

38. What does Redux describe as an action?

React requires that actions contain a type property that identifies the kind of action being taken. They must be specified as a String constant, and you can also give them additional characteristics. Redux uses functions referred to as Action Creators to produce actions.

39. Describe the Reducer's function?

Reducers are uncomplicated functions that describe how the state of the application changes in response to an ACTION. Reducers function by ingesting the prior state and action, then returning a new state. Based on the type of activity, it calculates what kind of update is required, and then it returns new values. If no work needs to be done, it returns the prior state exactly as it was.

40. What does the word "Store" mean in Redux?

The state of an application can be stored in a store, a JavaScript object that also offers a few helpful methods to access the state, send actions, and register listeners. The whole state/object tree of an application is saved in a single store. As a result, Redux is highly straightforward and dependable. To handle data processing and to preserve a record of different operations that alter the state of stores, we can pass middleware to the store. Through reducers, all operations return to a new state.

41. What distinguishes Redux from Flux?

• State and change logic is included in Flux The Store. Redux separates its store logic from its change logic.
• There are numerous stores in Flux. In Redux, there is just one shop.
• In Redux, all the stores are connected, while in Flux, they are all flat. One-storey reduction with hierarchical reducers
• Flux has a singleton dispatcher. In Redux, there is no concept of a dispatcher.
• React elements subscribe to the Flux store. Connect is used by container components in Redux.
• Flux's state is mutable. Redux has an immutable state.

42. What benefits does Redux offer?

Redux offers the following benefits:

• Predictability of Results- Since the store is always the only reliable source of information, there is no uncertainty over how to synchronize the current state with actions and other application components. 
• Maintainability- A predictable result and a rigid structure make the code easier to maintain. 
• Server-side Rendering- You only need to give the store built on the server to the client side to do the server-side rendering. This improves user experience while being very helpful for initial render and application speed. 
• Tools for developers — From actions to state changes, developers have access to real-time monitoring of everything occurring within the program.
• Community and ecosystem: Redux is supported by a sizable community, which adds to its allure as a tool. Many skilled people work together to improve the library and create many different applications using it.
• Easy Testing: Redux's code is largely made up of small, clean, isolated functions, making testing it simple. As a result, the code is independent and testable.
• Organization: Redux is quite specific about how code should be arranged, which makes it easier for a team to work with and more consistent.

43. Describe React Router?

React Router, a potent routing library developed on top of React, aids in expanding the application's screens and flows. By doing this, the URL is kept up to date with the information being presented on the website. It is used to create one-page web apps and maintains a uniform structure and behavior. React Router offers a straightforward API.

44. Why is a Router necessary in React?

When a user types a certain URL, the router checks to see whether the URL matches the path of any of the "routes" it has specified, and if it does, the user is forwarded to that particular route. Therefore, in order to add numerous routes, each of which leads to a different view, to our project, we need to install a Router library.

45. Give a list of React Router's benefits.

The following are some of the benefits of React Router:

React Router v4's API is "All About Components," much to how React is built on components. A Router can be seen as a single root component (BrowserRouter>) that contains the individual child routes (route>).

History value doesn't need to be manually set: All we have to do to use React Router v4 is wrap our routes in the BrowserRouter component.

The packages are divided into Each of the three packages is for Web, Native, and Core. This supports our application's small size. Based on similar coding styles, switching is simple.

46. What would you do if the rendering of your React application was slow?

The number of re-render operations, which are occasionally unneeded, is the primary cause of React's delayed rendering. React offers customers two key tools to assist them to achieve this:

memo(): This is employed to stop all pointless re-rendering by the function components.

Pure Component: In order to prevent the needless re-rendering of class components, PureComponent is employed.

47. What does React's StrictMode component do?

When employed, the StrictMode component would be of great assistance to users in building new codebases and comprehending the components.

It can, however, work effectively in debugging as well since, when wrapped with other components that might be the problem's source, it will speed up the resolution of the issue.

48. What distinguishes React's cloneElement and createElement commands?

CloneElement is largely used in React to copy an element and pass it directly to new props. CreateElement, on the other hand, is the entity into which JSX is translated. 

React elements are also created using this. 

49. Can you display props on a parent Component?

It is indeed feasible. The spread operator is the most effective approach to complete this operation. The properties can also be listed, although this is a complicated process.

50. Why is it necessary to capitalize on the components in ReactJS?

It is required since components are constructors and not DOM elements. They can cause a number of problems and confuse developers if they are not capitalized. The integration of some features and commands may also be a challenge.

These react interview Questions and answers will serve as a comprehensive guide to your interview.

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