Cognizant React JS Interview Questions

Here is the list of React JS Interview Questions which are recently asked in Cognizant company. These questions are included for both Freshers and Experienced professionals.

1. What is the main goal of React Fiber?

React Fiber is a complete, backwards compatible rewrite of the React core. The goal of React Fiber is to increase its suitability for areas like animation, layout, and gestures. Its headline feature is incremental rendering: the ability to split rendering work into chunks and spread it out over multiple frames.

2. What are controlled components?

In a controlled component, form data is handled by a React component. The alternative is uncontrolled components, where form data is handled by the DOM itself. To write an uncontrolled component, instead of writing an event handler for every state update, you can use a ref to get form values from the DOM.

3. What are uncontrolled components?

4. What is Lifting State Up in React?

In React, sharing state is accomplished by moving it up to the closest common ancestor of the components that need it. This is called “lifting state up”.

5. What are the lifecycle methods of React?

The few lifecycle methods of React

The render() method is the most used lifecycle method and handles the rendering of the component to the UI.
The componentDidMount() is called as soon as the component is mounted and ready. This is a good place to initiate API calls, if you need to load data from a remote endpoint.
The componentDidUpdate()is invoked as soon as the updating happens. The method is updating the DOM in response to prop or state changes.
The componentWillUnmount() is called just before the component is unmounted and destroyed.

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6. What are portals in React?

Portals provide a first-class way to render children into a DOM node that exists outside the DOM hierarchy of the parent component. The first argument ( child ) is any renderable React child, such as an element, string, or fragment.

7. What are the advantages of React?

Easy to Learn, Easy to Use.
Reusable Components.
It ensures faster rendering.
It guarantees stable code. SEO friendly.

8. What are the limitations of React?

React Technology accelerates so fast so that it cannot make proper documentation of the project. So, the developer tries to write the instruction on its own. React focus on the view part of MVC i.e. UI of the web application

9. What is the use of react-dom package?

The react-DOM package provides DOM-specific methods that can be used at the top level of the app and as an escape hatch to get outside of the React model if we need to. Most of the components should not need to use this module.

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10. How to use InnerHtml in React?

This rule applies when innerHTML prop for a React DOM element is used. InnerHTML prop is risky because it is easy to expose the users to a cross-site scripting (XSS) attack. React provides dangerouslySetInnerHTML as a replacement for innerHTML prop to remind you that it is dangerous.

11. How events are different in React?

Handling events with React elements is very similar to handling events on DOM elements. There are some syntax differences: React events are named using camelCase, rather than lowercase. With JSX you pass a function as the event handler, rather than a string.

12. How you use decorators in React?

Decorators in React help to take an existing Class component, or function of a Class component, and modify it, thereby allowing adding extra capabilities, without having to mess with the existing codebase. Modification can be overriding the existing function completely, or just adding extra logic to it.

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13. How to enable production mode in React?

Building your app for production

Enable Debugging over USB-Most Android devices can only install and run apps downloaded from Google Play, by default.
Plug in your device via USB-Let’s now set up an Android device to run our React Native projects.
Run your app

14. What is strict mode in React?

Strict Mode is a tool for highlighting potential problems in an application. Like Fragment. Strict Mode does not render any visible UI. It activates additional checks and warnings for its descendants.

15. What are React Mixins?

Mixins extend the class they are mixed into, while HOCs compose classes and return new classes. Mixins can set State in components since they are going to be part of that component. HOCs should not set State since they are only functions that take a class and return another class, they communicate through props instead.

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Cognizant React JS Interview Questions