React JS Interview Questions & Answers

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What is React JS?

React js is javascript based UI Library developed at Facebook, to create an interactive, stateful & reusable UI components. It is one of the most popular javascript frameworks that is created for handling the presentation layer for the web and mobile apps.

List some advantages of ReactJS ?

Advantages of React Js:- React.js is extremely efficient: React.js creates its own virtual DOM where your components actually live. This approach gives you enormous flexibility and amazing gain in performance. React.js also calculates what are the changes needed to be made in DOM. This process of React.js avoids expensive DOM operations and make updates in a very client manner. It makes writing Javascript easier: React.js uses a special syntax called JSX, which allows you to mix HTML with Javascript. The user can drop a bit of HTML in the render function without having to concatenate strings, this is another fantastic thing. React.js turns those bits of HTML into functions with a special JSXTransformer. It gives you out-of-the-box developer tools: When you start your journey with React.js, do not forget to install official React.js chrome extension. It makes debugging your application much easier. After you install the extension, you will have a direct look into the virtual DOM as if you were browsing a regular DOM tree in the elements panel. Isn’t it pretty amazing! It’s awesome for SEO: One of the biggest problems with other Javascript frameworks is that they do not search engine friendly. Though there have been some improvements in this area, search engines generally have trouble reading Javascript heavy applications. React.js stands out from the crowd because you can run React.js on the server, and the virtual DOM will be rendered to the browser as a regular web page. UI Test Cases: It is extremely easy to write UI test cases because the virtual DOM system implemented entirely in JS.

What are refs in React?When to use it.

In React ref is used to store the reference of element or component returned by the component render() configuration function.Refs should be avoided in most cases, however, they can be useful when we need DOM measurements or to add methods to the components. Refs can be used in following cases:- Managing focus, text selection, or media playback. Triggering imperative animations. Integrating with third-party DOM libraries.

Enlist the advantages and disadvantages of React js?

React.js is used by web developers for creating large web pages without reloading the entire page. It uses the data and can be changed over time. The following are the advantages of using React.js- 1- React makes Search engine optimization (SEO) easy. 2- It is very efficient as it ensures readability and easy maintenance. 3- It gives extraordinary developer tools to web developers and makes Java coding easier for them. 4- UI test cases. The following are the disadvantages of React- 1- Some major configurations are required for integrating React js with traditional MVC framework such as substituting erb with React js. 2- It is a steep learning process for people who are new to web development world.

What are the controlled components and uncontrolled components in React?

Controlled component is more advisable to use as it is easier to implement forms in it. In this, form data are handled by React components. A controlled input accepts values as props and callbacks to change that value. The uncontrolled component is a substitute for controlled components. Here form data is handled by DOM itself. In uncomfortable components, the ref can be used to get the form values from DOM.

Explain the difference between functional and class components?

Functional components- are those components that returns React elements as a result. These are just simple old JavaScript functions. React 0.14 has given a new shortcut for creating simple stateless components that are known as functional components. These components make use of easy JavaScript functions. Class components – most of the tech savvy people are more familiar with class components as they have been around the corner for a longer time. These components make use of plain old java objects for creating pages, mixins, etc in an identical way. Using React’s create class factory method, a literal is passed in defining the methods of a new component.

What is the use of arrow function in React?

Arrow functions are extremely important for React operations. It prevents this bugs. Arrow functions make it easier to predict the behavior of this bugs when passed as callbacks. They don’t redefine the value of this within their function body. Hence, prevents bugs caused by the use of this within callbacks.

What is the purpose of render() function in React?

render() function is used to update the UI. For this, you have to create a new element and send it to ReactDOM.render(). React elements are immutable and once you create an element, you cannot change its attributes. Thus, elements are like a single frame and it depicts the UI at some point. ReactDOM.render() controls the content of the container node you pass and if there is any DOM element already present in it then it would be replaced when first called.

Does Reactjs Use Html?

No, It uses JSX which is simiar to HTML.

When Reactjs Released?

March 2013

What Is Current Stable Version Of Reactjs?

Version: 15.5 Release on: April 7, 2017

What Are The Limitations Of Reactjs?

Limitations of ReactJS: React is only for view layer of the app so we still need the help of other technologies to get a complete tooling set for development. React is using inline templating and JSX. This can seem awkward to some developers. The library of react is too large. Learning curve for ReactJS may be steep.

What is Repository URL of ReactJS?

https://github.com/facebook/react

What is the difference between createElement and cloneElement?

createElement is the thing that JSX gets transpiled to and is the thing that React uses to make React Elements (protest representations of some UI). cloneElement is utilized as a part of request to clone a component and pass it new props. They nailed the naming on these two.

What is meant by event handling?

To capture the user’s information and other similar data, event handling system is considered. It is generally done through DOM elements which are present in the code. This task is simple to accomplish. Two-way communication is considered in this approach.

In ReactJS, why there is a need to capitalize the components?

It is necessary because components are not the DOM element but they are constructors. If they are not capitalized, they can cause various issues and can confuse developers with several elements. At the same time, the problem of integration of some elements and commands can be there.

What is redux?

A method os handling the state (or data) of an application.

What is one of the core types in React?

ReactNode

How is ReactJs different from AngularJS?

The first difference between both of them is their code dependency. ReactJS depends less to the code whereas AngularJS needs a lot of coding to be done. The packaging on React is quite strong as compared to the AngularJS. Another difference is React is equipped with Virtual Dom while the Angular has a Regular DOM. ReactJS is all about the components whereas AngularJS focus mainly on the Models, View as well as on Controllers. AngularJS was developed by Google while the ReactJS is the outcome of facebook. These are some of the common differences between the two.

What is JSX?

It is basically a novel dialect of the popular JavaScript that simply integrates the HTML templates into the code of JavaScript. The browser is not capable to read the code simply and thus there is a need for this integration. Generally, WebPack or Babel tools are considered for this task. It has become a very popular approach in the present scenario among the developers.