Capgemini – React JS Interview Questions

Here is the list React JS Interview Questions which are recently asked in Capgemini company. These questions are included for both Freshers and Experienced professionals. Our React JS Training has Answered all the below Questions.

1. ReactJs and Its features.

React JS is a JavaScript library that was developed by Facebook for the user interface in 2013. It is used for creating single page web or mobile applications. It is a powerful library that is optimal for fetching data which is rapidly changing. Its main function is data rendering.

Features of React JS

Virtual DOM, JSX.
One-way data binding.
React native, Declarative UI.
Component-based architecture.
Speed and efficiency, Flexibility.

2. Why should we use React, tell its advantages too?

Businesses that use React JS are assured of better performance compared to those that use other frameworks. Because React JS helps to prevent updating of DOM, it means that the apps will be faster and deliver better UX. React JS was designed to help improve the total rendered pages from the website server.

It facilitates the overall process of writing components.
It boosts productivity and facilitates further maintenance.
It ensures faster rendering and guarantees stable code.
It is SEO friendly, comes with a helpful developer toolset.

3. Enlist React limitations if you know any?

React is not a framework but a set of libraries.
Designers take time to understand this library as it is very large in size.
For novice programmers, it can be difficult to understand this library.
Inline templating and JSX makes the coding somewhat complex.

4. Explain Virtual DOM of React and how does it work?

The virtual DOM (VDOM) is a programming concept where an ideal, or “virtual”, representation of a UI is kept in memory and synced with the “real” DOM by a library such as React DOM. This process is called reconciliation. They may also be considered a part of “virtual DOM” implementation in React.

5. What is the difference between Real and Virtual DOM?

In React, for every DOM object, there is a corresponding “virtual DOM object.” A virtual DOM object is a representation of a DOM object, like a lightweight copy. A virtual DOM object has the same properties as a real DOM object, but it lacks the real thing's power to directly change what's on the screen.

6. What is JSX in React? Explain with example and proper syntax?

JSX in React is called JSX, and it is a syntax extension to JavaScript. We recommend using it with React to describe what the UI should look like. JSX may remind you of a template language, but it comes with the full power of JavaScript. JSX produces React “elements”.

7. Why Can Browsers not read JSX?

Browsers cannot read JSX because there is no inherent implementation for the browser engines to read and understand it. You can use label to transform your jsx into native JavaScript and HTML which browser can understand.

8. What is render () in React and why is it used?

The render() function in React displays the specified HTML code inside the specified HTML element. This function takes 2 arguments, namely HTML code and an HTML element, and returns a single element which is the representation of the native DOM component.

9. Differentiate between React and Angular.

Angular is a full-fledged framework, while React is a library. React. js uses virtual DOM and one-way data binding while Angular operates on real DOM & two-way data binding. There's also a difference in bundle size (React's smaller) and speed (React works a bit faster).

10. Define Props.

Props (short for properties) are a Component’s configuration. Props are how components talk to each other. They are received from above component and immutable as far as the Component receiving them is concerned. A Component cannot change its props, but it is responsible for putting together the props of its child Components.

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11. Define State in React and the way it is used in React.

State is a JavaScript object that stores a component's dynamic data and determines the component's behavior. Because state is dynamic, it enables a component to keep track of changing information in between renders and for it to be dynamic and interactive. State can only be used within a class component.

12. Compare props and state.

Props (short for properties) are an object of arbitrary inputs a React function component accepts as the first argument. State is data that changes over the lifetime of a specific instance of a React component.

13. Compare stateful and stateless components.

Stateless components are simple functional component without having a local state but remember there is a hook in react to add state behavior in functional component as well. Stateful component can contains the state object and event handling function, user actions as well.

14. What are the phases of the lifecycle of React’s component?

React lifecycle phases

Each component in React has a lifecycle which you can monitor and manipulate during its three main phases. The phases are: Initialization, Mounting, Updating, and Unmounting.

15. What is React.js? How is it different from other javascript frameworks?

The difference between JavaScript solutions (such as React. js) and older technologies is that JS takes over much more of the logic and document manipulation, just as if it was not server-rendered at all. The main feature of React JS that distinguishes it from other popular JavaScript frameworks is flexibility.

16. Explain lifecycle of a React component?

The lifecycle of a React component takes place within these events that are in four categories: Updating: Here the methods and events take place after the React component has entered the DOM. Un-mounting: Here the methods and events take place as they React component leaves the DOM or is unmounted from the DOM.

17. Have you used HTML while working with React.js?

With React, we write HTML using JavaScript. To rely on the power of JavaScript to generate HTML that depends on some data, rather than enhancing HTML to make it work with that data. Enhancing HTML is what other JavaScript frameworks usually do.

18. How to set up routing in ReactJS. Explain with the help of step by step approach?

React Router Tutorial

Step 1: Build an App. JS React component. In the src directory, create one component file called App.

Step 2: Make three components. First, make one components directory and in that make Home. js component.

Step 3: Register the routes in the App. JS file. // App.

19. How to use Events in ReactJS? Give an example of using events?

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.

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Capgemini React JS Interview Questions