The game changer in the dynamic environment of web development has been ReactJS, making it one of the most sought after JavaScript libraries. If you are a ReactJS developer, you may find yourself confronted with a number of ReactJS interview questions ranging from basic to advanced concepts.

Through this detailed article, we will delve deeply into numerous top interview questions for reactjs that can provide you with sufficient knowledge and confidence needed for your next technical interview.

ReactJS Interview Questions – Most Asked Beginner Level

As a beginner you need to know the most common react interview questions and answers, so you can pass your interview with a good impression. Here some react interview questions you may be asked:

1- What is ReactJS? What are its key features?

This is one of the common ReactJS interview questions for beginners, so if you were asked to answer here what you need to say:

React JS is a library made up of small components which facilitates building views. Some important attributes include component based architecture, virtual DOM and one-way data binding for efficient web application development.

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2- Can you Elaborate the lifecycle methods in ReactJS?

A number of life cycle methods exist for react js components that give developers control over various stages of a component’s lifecycle like mounting, updating or unmounting them. Examples of some commonly used life cycle methods include componentDidMount(), componentDidUpdate()…etc.

3- Differentiating between state and props in ReactJS

This is one of the react questions for interview, so you should know how to differentiate between those terms. State is an internal data of a component that can be changed from within the component itself. Props are input parameters that are passed down from parent components to child components which cannot be modified.

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4- Can you Define JSX in terms of ReactJS?

This is one of the react interview-questions for beginners, you can answer it by stating that JSX (JavaScript XML) is used as an extension for JavaScript language, which allows developers to write HTML-like code in their JavaScript files. This eases the act of creating and managing React component structures.

5- The purpose of the render() method in a ReactJS component?

One of the ReactJS interview questions for beginners is the purpose of render, to answer you can state that Render() function behaves like any other required method in a ReactJS component, it gives the UI elements that must be displayed into the DOM. It provides the real HTML structure of the component.

Top advanced reactjs interview questions

You need to know react js interview questions and answers for experienced developers to get prepared for your next interview. Here are the top react js interview questions for experienced:

1- Explain the concept of virtual DOM in ReactJS

As an experienced developer this may be one of the ReactJS interview questions.The virtual DOM is a lightweight representation of the actual DOM that resides in memory.

According to this, the subscribers are answered during the state changes in a component by ReactJS to update only necessary portions of real DOM based on comparing new virtual with old one. It enhances React application performance through reconciliation.

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2- What is the purpose of the keys prop in ReactJS lists?

Keys prop stands for direct entrance into elements of React list. They help efficiently track which element has been changed, deleted or added by React. When rendering and updating lists, using distinct keys can improve performance.

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3- Can you Explain the concept of controlled and uncontrolled components in ReactJS?

This is one of the advanced ReactJS interview questions, so you should state that Controlled components in react are those where the state is kept within the component while uncontrolled ones are those where the state is managed by the dom: Controlled Components offer greater control and flexibility while Uncontrolled Components are easier to set up.

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4- What is the purpose of the useEffect() hook in functional components?

This may be one of the ReactJS interview questions for experienced developers.The purpose of the ReactJS useEffect() hook in functional components is to mainly enable you to do side effects which may include fetching data, subscribing to events or making manual changes to DOM. It can be used in place of lifecycle methods like componentDidMount(), componentDidUpdate() and componentWillUnmount().

5- Explain Context API concept in ReactJS

Context API is a method for passing data through the component tree without having to manually pass props down at every level. Particularly when it comes to global-level state management like theming or user preferences.

React router interview questions

React routing interview questions is important when you are preparing for ReactJS interview questions, here are some of the Router react interview questions and answers:

1- What is the purpose of React Router?

It’s a library that manages routing in ReactJS apps, providing the ability to go through pages without full page reload, that way constructing single-page applications (SPAs).

2- How are the various components provided by React Router explained?

The major components offered by React Router include BrowserRouter, Route, Switch, Link and NavLink. With these components a developer can structure routes, display proper components based on the URL and create links for navigation.

3- What is the difference between Link and NavLink components in React Router?

When comparing Link to NavLink, while Link aids you construct hyperlinks leading to other pages/URLs; NavLink does similar things but uses “active” class name for styling when the current URL matches the one in “to” prop of a component.

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4- How do you handle dynamic routes in React Router?

React Router supports dynamic routes, which is a situation where the URL path may have some parameters. The parameters can be gotten by accessing the match.params object inside the component rendered by the Route.

5- Explain what the switch component does in React Router?

The Switch component in React Router ensures that only one Route is rendered at a time. It iterates through the child Route components and renders the first one whose path matches the current URL.

ReactJS Redux Interview Questions

Redux is a part of the ReactJS interview questions, so it’s important to get a grip of some of the questions regarding this section as a part of the react js interview preparation. 

1- What does redux do in a ReactJS application?

Redux works as an entirely predictable JavaScript applications state container. In a ReactJS application, Redux is usually employed for controlling global application state so that it is easier to work with complex states and flows of data.

2- What are the three principles of Redux?

The three principles of Redux are 1) Single Source of truth: The state for apps is kept within a single store. 2) State is read-only: In order to change the state, you must emit an action. 3) Changes are made with pure functions: Actions specify how the state tree is transformed by reducers.

3- What are the major components of a Redux application?

Actions, reducers and store comprise main components of a redux application. Actions define what happens in the app’s state; Reducers specify how actions change the state; Store manages the overall application’s state.

4- Define middleware in Redux.

Redux middleware are functions that can access an action and current app’s state. They can be used for different purposes like logging, exception handling or asynchronous actions.

5- How do you handle async actions in redux applications?

Usually asynchronous actions in a redux application are treated using middleware like redux-thunk or redux-saga. These middlewares make it possible to dispatch functions (thunks) or generator functions (sagas) which can perform some asynchronous operations and update the state accordingly.

Conclusion

Getting ready for a ReactJS interview could feel overwhelming but once you have excellent knowledge of both basic and complex subjects, you will confidently exhibit your skills. This article has contained within it, a wide variety of ReactJS interview questions that are asked to test candidates on their knowledge of ReactJS ranging from fundamental to more intricate scenarios. Once you master these questions, you are well on your way to excelling at your technical interviews hence moving your career as a reactjs developer to another level.