React Interview Questions and Answers

Ques 1. Can AJAX be used with React?

Yes, any AJAX library, such as Axios and jQuery AJAX, can be used with React easily. One important thing is to maintain the states of the components, and here too, the props are passed from the parents to the child components.

Child components still cannot send back props to parents, and this factor greatly increases rendering efficiency when dynamic data is considered.

Ques 2. What is the meaning of synthetic events in React?

Synthetic events in React are objects that act as cross-browser wrappers, allowing for the use of native events. This is done to ensure that a variety of browsers can run the API and that the event contains all properties.

Ques 3. What are stateful components in React?

Stateful components are entities that store the changes that happen and place them into the memory. Here, the state can be changed, alongside storing information such as past, current, and future changes.

Ques 4. What are refs in React?

‘Refs’ is short for references in React. Refs are used to store a reference to a single React element or a React component. This is later returned using the render function.

They are mainly used in the following scenarios:

• To initiate imperative animations
• To join third-party DOM libraries
• To manage focus and apply media playback

Ques 5. What are controlled components in React?

Controlled components in React refer to the components that have the ability to maintain their state. The data is completely controlled by the parent component, and the current value is fetched by making use of props. This is done to notify about any change that occurs when using callbacks.

Ques 6. Why is a router required in React?

A router is very much necessary in React as it is used to manage multiple routes whenever a user types in a URL. If the route is present in the router for that corresponding URL, then the user is taken to the particular route.

Ques 7. What are the components of Redux in React?

Redux consists of four main components as shown below:

• Action: An object that describes the call
• Reducer: The state change storage unit
• Store: the state and object tree storage
• View: Displays data provided by the store

Ques 8. What are the disadvantages of using MVC in React?

Among a plethora of advantages of using MVC in React, there are minor problems as stated below:

• A lot of memory wastage occurs.
• DOM manipulation costs a lot.
• The application becomes slow.
• Lots of dependencies are created.
• The complexity of models increases.

Ques 9. What are pure components in React?

Pure components are singular entities that are written in React. They are fast and simple to write and have the ability to replace a component that has only the render() function. This is done to ensure that the performance of the application is good and that the code is kept simple at the same time.

Ques 10. What are higher-order components (HOCs) used for?

HOCs are used for a variety of tasks such as:

• Manipulation of props
• State manipulation and abstraction
• Render highjacking
• Code reusing
• Bootstrap abstraction

Ques 11. Differentiate between a controlled component and an uncontrolled component in React.

A controlled component, as the name suggests, is a component over which React has complete control. It is the singular point of data for the forms.

An uncontrolled component is one where the form data gets handled by DOM and not the React component. This is usually done using refs in React.

Ques 12. How can you tell React to build in the production mode?

React can be coded to directly build into production by setting the process.env.NODE_ENV variable to production.

Note: When React is in production, warnings and other development features are not shown.

Ques 13. What is the difference between cloneElement and createElement in React?

In React, cloneElement is primarily used to clone an element and pass it to new props directly. Whereas, createElement is the entity that JSX gets compiled into. This is also used to create elements in React.

Next up on this top React interview questions and answers blog, take a look at the use of the second argument.

Ques 14. What is the StrictMode component used in React?

The StrictMode component when used would benefit users immensely while creating new codebases to understand the components being used.

However, it can fit well in debugging as well because it will help solve the problem faster when it is wrapped with other components, which could be causing the problem.

Next up on these interview questions on React JS, you have to understand how to speed up rendering.

Ques 15. What would you do if your React application is rendering slowly?

The cause of slow rendering in React is mostly because of the number of re-render operations, which are sometimes unnecessary. There are two main tools provided by React to help users here:

• memo(): This is used to prevent all of the unnecessary re-rendering carried out by the function components.
• PureComponent: This is used to ensure that the unnecessary re-rendering of class components is avoided.

Ques 16. Can you conditionally add attributes to components in React?

Yes, there is a way in which you can add attributes to a React component when certain conditions are met.

React has the ability to omit an attribute if the value passed to it is not true.

Ques 17. What are the predefined prop types present in React?

There are five main predefined prop types in React. They are as follows:

1. PropTypes.bool
2. PropTypes.func
3. PropTypes.node
4. PropTypes.number
5. PropTypes.string