Crayon Data – React JS Interview Questions

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

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

React JS is an open-source JavaScript library used for building user interfaces specifically for single-page applications. It's used for handling the view layer for web, mobile apps and to create reusable UI components.

React JS stand out because of many reasons in which it has a huge ecosystem with component based approach. It has separate library for handling DOM.

2. Can you explain about the standard JavaScript toolchain, transpilation, JSX?

A JavaScript tool chain is a set of software utilities used to perform an operation. For example, in program development, the tool chain to turn source code into a working machine language program includes a compiler, assembler, linker and debugger.

Transpilers, or source-to-source compilers, are tools that read source code written in one programming language, and produce the equivalent code in another language. This is called transpilation.

JSX is an XML/HTML-like syntax used by React that extends ECMA Script so that XML/HTML-like text can co-exist with JavaScript/React code.

3. Explain lifecycle of a React component?

Every React Component has a lifecycle of its own; lifecycle of a component can be defined as the series of methods that are invoked in different stages of the component's existence. The phases are: Initialization, Mounting, Updating, and Unmounting.

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

To include static html in React JS use html-loader plug-in if you are using web pack to serve your react code. Static html files can be used to load the html files in react.

5. How do you embed two components in one component?

In React, one element can be rendered. Even if we have multiple elements to render, there can only be a single root element. We have to wrap them in another element or component if we want to render two or more elements.

6. How might React handle or restrict Props to certain types, or require certain Props to exist?

When rendering the , we can pass in props (i.e. ).Props attributes can be passed it in JSX using the Spread operator which passes the whole props object. So when your intent is to pass the whole props object, that's fine to use.

7. How React component lifecycle methods help in building interfaces?

Components are the building blocks of any React app and a typical React. React element that describes how a section of the UI (User Interface) should appear. React DOM is a package that provides DOM specific methods. Use React to define and create your elements, for lifecycle hooks, etc.

8. How React Router and its techniques differ from more traditional JavaScript routers like Backbone’s Router?

Routing is a process in which a user is directed to different pages and React-router provides the core routing components and function. For Routing, open the index.js file and import all the three component files in it.

React Router uses dynamic routing. React Router, and dynamic, client-side routing, allows us to build a single-page web application with navigation without the page refreshing as the user navigates. React Router uses component structure to call components, which display the appropriate information.

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9. How to apply validation on Props in ReactJS? Apply validation in previously developed example in above question?

App.propTypes is used for props validation in react component. When some of the props are passed with an invalid type, you will get the warnings on JavaScript console. After specifying the validation patterns, you will set the App. default Props.

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

React JS - Router

Step 1 - Install a React Router.
Step 2 - Create Components.
Step 3 - Add a Router. add routes to the app.

11. 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.

12. How to use Forms in ReactJS? Give an example of using Forms in ReactJS by developing a User Registration Form?

React Forms

Add a form that allows users to enter their name: class MyForm extends React.
A simple textarea with some content initialized in the constructor: class MyForm extends React.
A simple select box, where the selected value "Volvo" is initialized in the constructor: class MyForm extends React.

13. How would you create Higher Order Components (HOCs) in React.js?

On mount, add a change listener to Datasource .
Inside the listener, call set State whenever the data source changes.
On unmount, remove the change listener.

14. Please explain step by step approach on how to setup environment for ReactJS?

Create the root folder
Install React and React DOM
Install web pack, babel
Set Compiler, Server and Loaders
Index.html
App.jsx and main.js
Running the Server
Generating the bundle

15. What are pure functional Components?

A React component is considered pure if it renders the same output for the same state and props. For class components like this, React provides the Pure Component base class. Pure Component class are treated as pure components.

16. What are react component lifecycle methods?

Every React Component has a lifecycle of its own; lifecycle of a component can be defined as the series of methods that are invoked in different stages of the component's existence.

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Crayon Data React JS Interview Questions