React JS Interview Questions
React JS Interview Questions

If you’ve been applying for a position as a React developer, you’ve likely already come across a handful of React JS interview questions. Although some of them may seem obvious, some interviewers are really just interested in your professional interests. The following React js interview questions will provide you with valuable insight into the workings of React. They’ll be much more interested in how you explain how React works in practice.


You might get asked about components in your React JS interview questions. You should know that all components must be grouped together, otherwise, the application would be bloated. Components must be simple and fast to use. In React, state is kept in the state property of each component. When a component renders, it calls the setState() method, which updates the state of the component. The component has full access to the form data, so it is important that you write simple code.

You should know that React is a small library focused on building UI components. It is often called the “V” in the MVC architecture. It can integrate itself seamlessly into any application, including websites, mobile applications, and desktop applications. Whether or not you’ve worked with React before is up to you. The question below will help you answer this question. In the following paragraphs, we’ll discuss some important components you’ll need to know.

The first component you need to learn is the arrow function. This function helps you properly bind the context components of your application. In JSX, arrow functions are used for this. When a component gets clicked, it gets attached to a child component. Using the arrow function, you can create a child component and pass the parent component all of its props to it. The child component will inherit the arrow function.

Another component you need to learn is the virtual DOM. The virtual DOM is a copy of the real DOM. If you don’t explicitly assign a key to a component, React will use it. This can have a negative impact on performance and state. To learn more about the benefits of using indexes, check out this article by Robin Pokorny. It will help you understand how these components work.


You might wonder what Observables are and how to use them in your React application. Observables are classes that keep track of data and change it whenever it reaches a certain threshold. A typical example is a form. It accepts values as props and callbacks, and it can be cloned and passed new props. These are just a few of the many interview questions about Observables.

Observables are collections of data elements that can be transformed into an object using the map and filter operators. Each of these operators depends on whether the data being observed matches certain criteria. The merge operator combines multiple observables and emits a value when one finishes. Similarly, the concat operator starts with the next observable when one ends. In addition to that, the from operator converts an array or an iterable into an observable. The from operator takes a single argument and emits all the contained values as a sequence.

Observables in React are the same as the ‘native’ events in the Java world. They are cross-browser APIs and wrap native event logic in one. The benefits of using synthetic events are that you can combine the behavior of different browsers into a single API and ensure that properties are consistent across browsers. For example, if you are using Angular, you may want to use RxJS with this framework.

As you may have guessed, Observables are a great way to share data or resources. But how can you use them in your application? Read on for some tips. There are many Observables in React. The Observable operators are map, filter, reduce, try/catch, and async/await. Observables are great for sharing data, but Promises don’t allow you to retry functions because they require an original function.

Lifecycle hooks

In React JS interviews, one question that may be asked is: “What are lifecycle hooks?” This is a question that asks the candidate to describe React’s lifecycle of components. The purpose of a hook is to perform a specific action, such as rendering a component. This action can only be performed on the top level of a component. Hooks cannot be called from standard JavaScript functions or from other components in the same component.

Lifecycle hooks are functions that get triggered by changes in a component’s state. These functions are called by the component’s constructor before it can render or unmount itself. The first two of these methods are used to define an initial state and props. The third phase, known as mounting, is called after initialization is complete. After the mounting phase, the component is mounted on the DOM and rendered. React follows a standard naming convention. Functions with “Will” or “Did” in their names refer to the phases before or after a component’s creation.

A lifecycle hooks question is a great way to gauge a developer’s personality and skills. A developer who understands the requirements is more likely to provide a list of tools and libraries. A developer with a passion for software development will likely offer a long list of tools and libraries they use to make their code. Debugging tools and community involvement are also good indicators of a passionate developer.

The other question that should be asked is “What is lifecycle?” This question will demonstrate whether the candidate is familiar with lifecycle hooks in React. A lifecycle hook is an action that can trigger React to re-render the component when its state changes. But a lifecycle hook can also prevent a component from being rendered if its state remains the same. Therefore, the “ShouldComponentUpdate” method should be interpreted carefully.


One of the common questions asked in React JS interviews concerns the use of reducers. Reducers are a type of data structure, which keeps state information for each object that is used in an application. When a user makes a request, they are routed to that object. Then, as the request is processed, the user is taken to another route. However, there are some disadvantages to using reducers, which can make the application slow or unusable.

To make your application more scalable, you should consider using Redux. It is a library that stores application state in a single location, which makes it easier to debug and inspect your application. The store stores the data of the application’s components. The View is the component that displays this data. You should know the difference between a view and a reducer. In most cases, you can use a reducer with a React application to achieve the same goal.

When using React, you should also learn about virtual DOM (VDOM). This is the name given to a copy of the real DOM. The virtual DOM contains elements, attributes, and properties. The render function of React creates this node tree and updates the data model when there are changes. These changes are normally made by users but can also be caused by system actions. React’s single-direction data flow model makes it easier to use it in web applications.

Redux + React set-up has a few common questions that should be asked during your Redux interview. These questions cover everything from the basics to the more complicated ones. Also, make sure you know how to organize code into reducers and how to use them to your advantage. If you can do this, you’ll be well on your way to success. You’ll be glad you did!

Document Object Model

If you are considering applying for a job in web development, you might find the Document Object Model (DOM) and ReactJS to be the most relevant technologies to prepare for. These technologies allow you to develop dynamic and rich user interfaces. They use state, an object that stores data and controls the rendering of a component over time. These objects change according to the user’s actions or system-generated events.

If you are going to be interviewing a developer in ReactJS, you may want to ask about his coding style. Ask how much effort he puts into understanding the requirements and if he’s willing to share which libraries he uses. You might also want to check how involved he is in the community. If he’s involved in community projects, he’ll likely be willing to share his experiences and lessons-learned with you.

When designing a web application, remember to take into account the ReactJS framework’s state management. ReactJS’s “ShouldComponentUpdate” method needs to be carefully considered. In some cases, the component won’t be rendered until the user changes the state of it. Therefore, you should make sure that you’re aware of this limitation in advance. As an example, you might want to use a “ShouldComponentUpdate” method to prevent the component from rendering if it is no longer updated.

The DOM is the core of the React framework. React allows you to create reusable UI components that allow you to have maximum flexibility. With React, you can also create arrays of fixed-number elements and user-defined data types. Another advantage of React is its reliance on JSX, which provides syntactic sugar for the language. If you’re unsure of how it works, ask your interviewer if you’d be happy using it in your web application.


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