React is one of the fastest-growing JavaScript frameworks in the market today. If you are an aspiring front end developer, we have compiled some important React interview questions that will help you learn all the major concepts.
Building user interfaces for single-page or mobile applications becomes comfortable with React. And you are most likely to be quizzed about this tool in job interviews. React certifications and crash courses are also in high demand due to this very reason.
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So, here are the top React interview questions to help you make an excellent first impression.
Top React Interview Questions and Answers
1. Compare real DOM and virtual DOM
Although real DOM updates slow, it can update HTML directly. It creates a new DOM if an element updates. However, DOM manipulation is costly in this case and can cause substantial memory wastage.
Virtual DOM can update faster and updates the JSX if element updates. It cannot directly update the HTML. But DOM manipulation is easy in this programming concept. And there is no issue of memory wastage.
Refer to the below-mentioned table to understand the differences-
| Real DOM | Virtual DOM |
| Updates slow. | Updates faster. |
| Expensive manipulation | Less expensive manipulation. |
| Has the ability to directly update HTML. | Does not have the ability to directly update the HTML. |
| Creates a new DOM on element updates. | Updates JSX when element updates. |
| Memory wastage | No memory wastage |
| Represents the UI of the application. | Only a virtual representation of DOM. |
This is one of the most basic react interview questions. Make sure to prepare well, and it will be the most asked react js interview question 2024 too.
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2. Explain React in simple terms
This is one of the most common React js interview questions. React is a JavaScript library developed by Facebook in the year 2011. It became open-source in 2015, gaining popularity among a community of individual developers and companies. React comes handy in the development of complex and interactive mobile and web UI. It uses a component-based approach for building reusable components.
React is a declarative, flexible, and efficient Javascript library. It is used primarily to build composable user interfaces. It is a powerful JavaScript UI library for creating modern applications.
Reusability, smooth testing, virtual DOM, easy data flow, simple migration, performance boosts are some of the reasons behind React’s wide adaptability.
React features-
- It is declarative.
- It is simple and powerful.
- It is extensible.
- Supports server-side.
- It is component-based.
- Supports mobile- support.
While answering the react js interview questions, make sure to structure your answers in this way. Additionally, the interviewer could also ask you about react project ideas.
3. List some features of React
React uses virtual DOM and server-side rendering. Also, it follows the principle of data binding, which is a unidirectional data flow. These three features provide a clear overview of React.
Features to mention during reactjs interview questions are discussed below-
- Virtual DOM- Creates a virtual copy of the original DOM. It is much quicker as compared to the original DOM.
- JSX- Makes writing React components easier.
- Flexibility-
- Speed-
- Declarative UI- It makes the code more readable and easier to debug.
- One-way data binding- Follows a single direction sending of the information, thus giving authority over information transfer.
- Component-based architecture- It defines visuals and interactions in applications.
This is how you can respond to the react interview questions and answers.
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4. What are the advantages of React? Also, list some of its limitations.
React is not difficult to integrate with other JavaScript frameworks like Meteor, Angular, etc. Writing test cases of UI becomes convenient with this tool. It is an easy tool to use for both the client and on the server-side. Another advantage of React is that it improves app performance. Also, the code has high readability due to JSX.
Now let’s look at some disadvantages.
Firstly, React is a library and not a full-fledged framework. Inline templating and JSX can make the coding complex, which can be a task for novice programmers to grasp. Since the React library is vast, understanding it can be a time-consuming process.
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Refer to the below-mentioned table to understand the advantages and disadvantages of React-
| Advantages | Disadvantages |
| Reusable components | JSX acts as a barrier |
| Easy to learn and easy to use. | The higher pace of development. |
| Has virtual DOM. | Poor documentation |
| SEO friendly | Poses problem with SEO |
| Shorter development time. | Steep learning curve. |
| Third-party libraries | Has long loading times. |
5. What is React JSX?
JSX is the short form of JavaScript XML. It converts HTML tags into React elements, capturing the expressiveness of JavaScript with a syntax like HTML. JSX converts HTML tags into react elements. Such a type of file is easy to understand and results in robust and high-performance applications.
Benefits of using React JSX-
- SEO friendly
- React Hooks
- Virtual DOM
- Highly efficient
- Open- source
- Reusable components
- Enhance performance
- Code stability
- Easier to write with JSX
- Strong community support
This is how you can respond to react interview question by making a mention of features along with the definition.
6. Can browsers read JSX?
No, browsers can only read JavaScript objects. So, we need to enable the browser to read the JSX. This exercise involves converting the JSX file into a JavaScript object before passing it on to the browser. Transformers like Babel can be used for the same.
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7. Explain the working of virtual DOM
A virtual DOM is initially a lightweight copy of the real DOM. It is a JavaScript object in the form of a node tree. The render function in React creates a node tree from the React components containing the elements, attributes, and object properties. Various actions by the user or system cause mutations in the data model and update this tree. The three-step process in virtual DOM works in the following way:
- The entire UI gets re-rendered when the underlying data changes
- Then, the new virtual DOM representation is compared with the previous one, and the difference is calculated
- The real DOM is updated considering the actual change or difference
8. Differentiate between React and Angular.
Angular uses the real DOM and two-way data binding as compared to the virtual DOM and one-way data binding in React. It has run-time debugging and not compile time debugging like React. Also, Angular is maintained by Google, while React is a Facebook product.
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Refer to the below-mentioned table to understand the differences-
| React | Angular |
| It is simplified. | It is complex. |
| Written in JavaScript language. | Written in Microsoft’s typescript language. |
| Latest version is 16.7.0 | Latest version is 7.2.0 |
| Framework is used in web applications. | Framework is used in mobile applications. |
| Strong abstraction | Medium abstraction |
| Faster documentation | Slower documentation |
This is how you can respond to the react js interview questions and answers.
9. “Everything is a component in React.” Do you agree?
The user interface of a React application is made up of building blocks called components. The components break the entire UI into independent, reusable pieces. These fragments are then rendered independently of the rest of the UI.
10. What is the purpose of render() in React?
Each component in React has a render(), which returns a single element representing the native DOM component. Elements are grouped together when more than one HTML element has to be rendered. The elements are grouped inside closing tags like <group>, <form>, <div>, etc. Whenever invoked, this function must return the same result.
These were some general React interview questions and answers to assist you in your preparation. Let us cover some more to develop more understanding of the concepts.
11. What are props in React?
Properties are called ‘props’ in React. These are read-only, and immutable components passed down from the parent to the child throughout the application. It is integral to maintain the unidirectional flow of the data, especially when it is generated dynamically. Therefore, the child component cannot send props back to the parent component.
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12. Explain state in React
State is the heart of a component in React that is accessed using this.state(). States are basically the source of data that determine the components’ rendering and behavior. Unlike props, states are mutable objects that create interactive components.
Properties of State in React-
- Stores a component’s dynamic data.
- It is dynamic in nature.
- Keeps a track of changing information in between renders.
- It is private to a component.
- It is immutable in React.
- It should never be altered or changed.
This makes for a commonly asked reactjs interview questions and answers for experienced.
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13. What are the phases in the lifecycle of a React component?
The lifecycle of a React component has three main phases. These are:
- Initial Rendering: The component makes its way to the DOM.
- Updating: The component updates or re-renders as props or state changes occur.
- Unmounting: Component is destroyed and removed from the DOM.
14. How are refs used in React?
We can return references to a particular element returned by render(). Refs attribute makes this possible. So, refs store a reference to a React component to be returned by the render configuration function. We generally use refs to add methods to components or measurements to DOM.
15. Controlled vs. Uncontrolled components
The primary difference between controlled and uncontrolled components is that the former get their current values through props and the latter through refs. Controlled components do not keep their own state as changes can be notified via callbacks. The parent component controls their data. On the other hand, uncontrolled components maintain their state, and the DOM controls their data.
Refer to the below-mentioned table to understand the difference between the two-
| Controlled Components | Uncontrolled Components |
| Parent component holds control over the data. | DOM itself holds the control over the data. |
| Stores the current value in the form of prop. | Use ref for the current values. |
| Allows substantial control over the elements. | Allows limited control over the elements. |
| Predictible | Not predictible |
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16. Explain events in React
In React, specific reactions like the keypress, mouse hover, clicks, etc. trigger reactions known as events. An event argument contains its own set of properties and behavior, capable of being accessed by the event handler alone. Events are passed as functions and named using the camelCase. This is a part of the important Reactjs interview questions list.
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17. What do you mean by Flux?
Flux is an architectural pattern that provides stability to the application by reducing run-time errors. It uses a central ‘store’ to enable communication between different components, maintaining authority over the data. All updates throughout the application must occur here only.
18. What is Redux? What are its components?
This is one of the most important Reactjs interview questions. The interviewer wants to check your knowledge of JavaScript components before they hire you. Redux is a predictable state container used for state management of JavaScript applications. It uses a single state tree or ‘Store’ to stock the entire application’s state in one place.
Redux is composed of the following parts:
- Action: An object describing what happened
- Reducer: Determines how the state will change
- Store: Tree of the entire application comprising objects and states
- View: Displays the data given by the Store
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19. What is the significance of Reducers?
Reducers specify how the application’s state would change in response to specific actions. Based on the type of activity, reducers determine what updates are required and then return new values. They return the same previous state if no change is necessary.
20. What is a React Router?
React Router is a routing library that helps add new screens and flows to JavaScript applications. You add this library to your app to create multiple routes, each leading to a unique page. The URL matches what is being displayed on the web page.
With this, we have covered most of the React interview questions that you will face in any interview. Being thorough on all these themes will help land that front-end development job!
Advantages of using React –
We have read that asking about the advantages of React is one of the react js interview questions that is almost always asked. If you understand the advantages in detail, you will always ace the question.
- Declarative in nature
Significant data changes are made possible via React, which causes chosen user interface elements to update automatically. You don’t need to undertake any additional tasks to update your user interface because of its progressive feature. During React interview questions, you must be thoroughly familiar with the nature of the interface.
- Accurate Predictions
Significant data changes are made possible via React, which causes chosen user interface elements to update automatically. You don’t need to undertake any additional tasks to update your user interface because of its progressive feature.
- Ability to test
The ability to test an application by keeping the code testable is one of the numerous advantages of React.js for app development. To put it another way, developers are able to assess the app’s usability across a range of devices by keeping the ability to test it. In order to carry out appropriate testing within your development team, data monitoring and speedy debugging are effective methods in app development. Be sure to test your app before you sit for React interview questions.
- React components are reusable
React offers reusable components that programmers are free to utilise to build new applications. For developers, reusability functions just like a cure. This platform allows the developers the freedom to repurpose parts created for one application for use in another with similar functionality. lowering the work required for development and guaranteeing perfect functioning.
- Library of JavaScript
The usage of a powerful JavaScript and HTML grammar mix streamlines the entire process of developing code for the intended project. The JS library has a number of functions, one of which translates the HTML elements into necessary functions and simplifies the overall project.
- SEO-friendly
After extensive investigation and development by Facebook, React was released. It stands out from the competition and enables designers to create outstanding, search-engine-optimized user experiences for all browsers and engines.
- Components Support
React is the ideal fusion of HTML elements and JavaScript. Utilising HTML elements and JS codes makes it simple to manage a sizable collection of data that contains the document object model. ReactJS serves as a mediator during this period, acting as the DOM’s (Document Object Model) representative and helping to determine which component changes are necessary to obtain the desired effects.
- Data Binding
One-way data binding is behind ReactJS. This indicates that every modification made to any specific data segment may be tracked by anyone. This represents how straightforward and easy it is to use.
This was our attempt to showcase top 20 react interview questions to you, make sure to always structure your responses and stay confident while responding.
Career opportunities for React developers –
There are numerous and increasing career opportunities for React developers. In all regions and business sectors, React developers are in demand. To be successful in your field, you must have refined React JS skills.
You must present your portfolio if you want to be considered for the position. The greatest method to demonstrate your talents is to tackle real-world tasks and develop applications that are used in the physical world. Due to its broad nature, React JS has recently become quite popular among digital businesses all around the world.
Many large firms are implementing React and are continually enhancing their user experience. The following is a list of some of the top employers who can ask React interview questions for front-end developers:
- Netflix
- The New York Times
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