Top 50 React JS Interview Questions And Answers

React JS is a Facebook Framework developed to create Web Applications. ReactJS allows developers to create reusable UI components. It is presently one of the most popular and powerful JavaScript libraries and has a robust foundation and a large community of users behind it.  Complete a list of frequently asked to React JS Interview Questions and answers by NSCHOOL Academy. We hope these React JS Interview Questions and answers are useful for your interview The below explained queries will help Users (also developers) to have a strong ideology on ReactJS. If you are preparing for a Job Interview, you’ll find these ReactJS thoughts helpful. Hope you’ll feel firm by the end of the session working with ReactJS.

1. Mention the features of React?

The features of React are JSX, Components, Virtual DOM, One-way data binding, and High performance.

2. How will you use JSX?

By using JSX Functionality, we can inscribe HTML tags like adding the header and user-defined tags in the same file that contains JavaScript codes.

3. Is JSX directly readable by web browsers?

No. Web Browsers are unable and don’t read JSX directly. Because they are built-in with readable regular JS objects. But there is one step to make web browsers read JSX. It’s by transforming the Modern JavaScript into a regular JavaScript object.

4. What is DOM? Explain.

DOM means Document Object Model. This DOM is a normal HTML document with a logical tree structural representation. The tree branches end in a node, and each node holds the objects.

5. What is Virtual DOM?

React JS keeps the Real DOM in memory as a Lightweight representation. This is called Virtual DOM.

6. What Factors vary between ES5 and ES6 standards?

Function and its components, exports vs export, and require vs import are the important factors that vary between ES5 and ES6 standards.

7. Explain the advantages of React JS.

-Readability and writing codes becomes easier as it uses the JSX feature. -Improvement in application performance because of the usage of virtual DOM -Integrated frameworks provide simpler works. -Server-side and client-side scripting is easy because of shared performance (Integrated Frameworks). -JS advanced tools pace the Integration and Unit testing performance.

8. In what ways React is different from Angular JS?

React is different from Angular JS with the following features. -DOM usage -Programming Language -Data Binding -Structure and design of applications. 9. Is React JS using HTML? No, React JS doesn’t use HTML. It uses only JSX which is similar to HTML. 10.Mention the lifecycles in React JS? – Initialization – State/Property Updates – Destruction 11. When ReactJS was released? ReactJS initial release was in March 2013. 12. How ReactJS is different from AngularJS? The main and the primary difference between both of them is their code dependency. The next difference is React is furnished with Virtual Dom while Angular has a Regular and usual DOM. In ReactJS you’ll learn all about the components whereas AngularJS has detailed descriptions mainly on the Models, View as well as on Controllers. ReactJS is less dependent on code whereas AngularJS requires lengthy coding to be done. The Application package on React is pretty strong as compared to AngularJS. Facebook is the developer of ReactJS and AngularJS creator is Google. 13. Explain Redux. Redux is one of the most powerful and demanding libraries for front-end development in today’s app development market. Redux size is very smaller and has no dependencies. Redux is actually the most anticipated state container that is purposely designed for developing JavaScript applications and it manages the entire states of the application. It is used to build applications that are easy to deploy in diverse environments and makes testing very simple and efficient. 14. Mention the usage of Redux Thunk. Basically, Redux thunk acts as middleware which allows developers to modify actions that return functions inturn and instead of actions. Redux Thunk is also used as a delay function to delay action dispatch if any of the certain conditions are met. There are 2 vital store methods as getstate() and dispatch() to provide parameters to inner functions. If you want to activate Redux thunk, then you must first use applyMiddleware() method. 15. Explain Flux. Flux is a simple and fundamental depiction that helps to uphold the unidirectional data stream. It controls interpreted data fragments and makes them interact with the data with no issues. Flux structures are dull and vague. So it is not specific to react applications. Flux is basically an upfront idea, where you have to showcase an intense conception of its usage. 16. Tell the current ReactJS version.? The current stable version of ReactJS is 16.12.0 17. Mention the current repository URL of ReactJS. The currently used repository URL of React JS is https://github.com/facebook/react 18. Explain the State in React JS and its usages? In ReactJS, State is depicted as an object that denotes the component characterization and its behavior. States are defined as the foundation of data that allows you to generate dynamic and interactive components. They are accessible using this.state() method. This method is used to change the value of that particular state object.

19. Explain the component lifecycle in ReactJS?

Basically, the Component lifecycle acts as an important accessory in this ReactJS platform. They contain lifecycle events that are divided into three primary classifications which are property updates, Initialization, and Destruction. In general, they are considered as the method to manage the states and properties of all its components. 20. Explain Props in ReactJS. Props depict the properties of ReactJS and are simply used to pass information from one component to another. But the data the Props are passed is passed in a unidirectional flow only. That is in a one-way path from parent to child. Also, they are only Readable data, which means child components will not be able to change data that comes from the parent. 21. What is meant by the higher-order component? High order component in ReactJS can be defined as the function used to collect the mandatory components and returns a new component. These new components act as the arrays that are usually extracted from React’s compositional nature. One important feature to be noted in this component is that it is used as a recyclable component logic in React. It helps us in identifying the best way to share behavior among the different array of React components. 22. Tell us about the synthetic events in ReactJS. Synthetic events in ReactJS are introduced mainly to improve the consistency and performance of interfaces and applications. There is a term called Synthetic event that acts as a cross-browser enveloped around the browser’s native and natural event. It integrates the behavior and actions of several browsers into a single standalone API to ensure their events act with the same and actual properties across diverse platforms and browsers. 23. What do you mean by Event handling? The event handling approach is taken into consideration when developers record the user details (for official purpose) and their related content. It is usually carried out with the help of DOM elements present in the code. It’s a simple task to complete quickly because developers use 2-way communication in this approach. 24. Mention the demerits of these React JS that you feel? Yes. React JS do have few demerits. One such thing is its enormous library size. Developers may consider this to be complex. Inline templates are the mystifying concept that many fresher developers feel. Another demerit will be one layer cover of the app. Developers are Testers also feel this as a time-consuming concept. 25. Mention in which platform React and ReactJS work? React is used for creating mobile applications (Android, IOS) and React JS is a framework built to develop web applications. So, from the above explanations, you would have got an idea about ReactJS. These are considered to be the overall view of this ReactJS Framework. Let us see more additional questions for the experienced ReactJS developers face in the interview. 26. Mention the important difference between Props and State. One such primary difference is State is Mutable(Changeable) and Props are Immutable. 27. Explain the term polling. Any Kind of server must be monitored 24/7 with at most caution. Through this regular examining process, we can check if any new or the presence of any fake alerts or comments. This process is ultimately termed as polling. Polling checks and monitors alerts or updates every 5 seconds. Also, we can physically change (increase/decrease) this time limit easily. The polling process is actually interesting, where Developers/Support team can make sure that there is no presence of any negative information (alerts/comments/updates) present in servers. Actually, those negative alerts can lead to high concerns. So, Polling is considered to be important in application development areas. 28. When there would be a necessity to use the Class component and Functional component? If our used component contains a state or lifecycle method we can use the Class component or else the Function component could be used. 29. Explain the differences between MVC and Flux. Flux is a newly updated feature in ReactJS as it overtook the MVC performance. Though MVC has the capability to handle data alarms, UI, and controllers, many of our developers find it a little complex to work when the mobile application size becomes high. But Flux is designed to work with any platform irrespective of its size. But, In general, MVC was eliminating the shortage in data integrity. 30. Why do you feel React Js has become more popular nowadays? ReactJS can be considered as a right-hand technology that can be processed for complex tasks. While running codes through ReactJS, even freshers and developers don’t need to bother about the bugs. After coding and compilation, this technology always certifies error-free outcomes. The ultimate part is that it delivers the best and scalable apps in turn. It is an accelerating and striking technology and can honestly be trusted for quality results. 31. Mention the important functionality between createElement and cloneElement. createElement in React JS is used to make React Elements and cloneElement is applied as a part of request call to clone any component and pass it into new props. 32. How many outermost elements can you use in JSX expression? If you want to fasten the process, you can use one JSX element. Using more than 2 elements generally slows down the process. If you are a fresher in this technology, then you might get jumbled with the usage of more elements and expressions. 33. Explain the key features and uses in Flux? Applications built on the Flux model have essential components that can be tested very easily. By simply updating the storage, developers could manage, monitor, and test any react component. It brings down the rate of data affection. The flux makes our mobile applications highly scalable and they do not suffer from compatibility issues. 34. What is meant by controllable and uncontrollable components? The components which do NOT maintain any internal state are said to be controlled components in ReactJS. Uncontrolled components are those components in the ReactJS that manage and maintain their own internal state. Internal state management makes the main difference here. 35. Tell us about React Router. Representation of components is an important and foremost task in ReactJS. React router decides which components to render(represent) and which one should not render. During several activities, it performs the Transcription process too. 36. What will you do if your expression contains more than one line? If our expression contains more than one line, enclosing and adding the multi-line JSX expression will be an option. If you are a fresher, enclosing it might seem uncomfortable but later you can understand everything fits in for the purpose. But, make sure to avoid multiple lines to complete the task easily and to get the desired and reliable outputs efficiently. So, avoid unnecessary multiple lines. 37. Explain the possibilities to use the word “class” in JSX? It is not possible to use the word ‘class’ in JSX. Class word is a default used word in JSX protocols. But remember, you can create your own ClassName as usual depending on the project requirements. Using the word Class will convert your JSX document to an immediate JavaScript document. 38.Tell us one of the core types in React? React node is one of the core types in React. 39. Explain to us the possibilities to display props on a parent component? Displaying props on a parent component is possible. One of the consistent way to conduct this task is by the usage of the spread operator. You can also list the properties but that’s way more a complex and lengthy process.

40. Why do you capitalize on the components in ReactJS?

It becomes necessary to capitalize because components are not considered as the DOM element but they act as constructors. If components aren’t capitalized, it might confuse the developers with varied elements. 41. Tell us in detail about Node Diffing. When you render the components more than once, Virtual DOM automatically checks the updated and modified elements. Then, they represent and display that modified element on the page. But, we have to understand that some elements refuse to take up the modification changes. So, to eliminate or cut down those changes to DOM, Node Diffing is recommended. Node Diffing also enhances browser performance. 42. Why do you use Effect in React? ‘use side effect’ is the full form for use Effect. Effects are based on when our application reacts with the outside world, like working with an API and accessing its output. Use Effect allows developers to combine methods like componentDidMount and componentDidUpdate. 43. Explain how Hooks work in React Js? Hooks are said to be functions of React JS. This function allows you to get hooked into the React state and lifecycle methods from functional components. Hooks doesn’t let developers work inside classes. Developers can design their own Hooks for reusing functional behavior between different components.

44. Can you nest JSX elements into other JSX elements?

Yes, you can nest JSX elements into other JSX elements. The process is similar to that of nesting the HTML elements. When you want to apply this task, then you must be more accustomed to the source and destination elements to carry out this task easily and efficiently. 45. What do you mean by Prop Drilling? When you are developing an application in React, you have to always go for a deeply nested component to work on with the data provided by another component that has a top hierarchy and top priority. This is called Prop drilling. To avoid prop drilling, you have to use React Context. 46. Why do you use the strictmode component? Strictmode component is included in ReactJS to provide supplementary perception to view possible issues in components. Developers use Strictmode component to ensure ReactJS follows all the best standard rules in application development. 47. Tell us some approaches in styling a React application? Some commonly used approaches for styling React-based applications are, -CSS and Inline classes -Preprocessors like Sass, Less, and Stylus -CSS in JS modules such as Styled components, Styled JSX. 48. Mention us important features that ReactJS is built upon. The React JS framework is built in the Open-source, Component-based, and Front end library. 49. Tell us what do these 3 dots (…) specify in React js? These (…) dots are used to pass props to a React component. 50. List the basic and additional Hooks in React JS? Some of the basic and built-in hooks are useState(), useEffect() and useContext() And some additional hooks are useReducer(), useCallback(), useMemo(), useRef(), useLayoutEffect(), useDebugValue() FINAL THOUGHTS FROM NSCHOOL We tried to cover all the substantial questions and hope that this article has helped you to grasp the REACTJS interview questions right from basics (freshers) to advanced (experienced developer)level. The above series of interview questions on ReactJS will enable you to crack any ReactJS queries. To have detailed and in-depth training (Hands-on practice) consider taking ReactJS training with NSCHOOL. Our practical environment gives you the confidence to gather the tenured experience right from the training stage.