React js Interview questions and answers Every brand wants to build an interactive UI for its mobile users as it engages them for a longer period and results in more conversions. Thus, brands pick the best talent from the developer community and offer them attractive packages. In case you are a developer who is willing to join the industry, here are a few React.js interview questions that answers about all the major elements of React Js.
1. What is ReactJS? 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 <https://www.onlineinterviewquestions.com/javascript/> that is created for handling the presentation layer for the web and mobile apps. 2. 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. Source: http://www.pro-tekconsulting.com/blog/advantages-disadvantages-of-react-js/ 3. What are Components in ReactJS? React Components let you split the UI into independent, reusable pieces, and think about each piece in isolation. Conceptually, components are like JavaScript functions. They accept arbitrary inputs (called “props”) and return React elements describing what should appear on the screen. Below is ample component written in ES6 class to display a welcome message on the screen. class Welcome extends React.Component { render() { return <h1>Hello, {this.props.name} </h1>; } } const element = <Welcome name="Sara" />; ReactDOM.render( element, document.getElementById('root') ); source: https://facebook.github.io/react/docs/components-and-props.html 4. What is JSX? JSX is an XML/HTML-like syntax used by React that extends ECMAScript so that XML/HTML-like text can co-exist with JavaScript/React code. The syntax is intended to be used by preprocessors (i.e., transpilers like Babel) to transform HTML-like text found in JavaScript files into standard JavaScript objects that a JavaScript engine will parse. Basically, by using JSX you can write concise HTML/XML-like structures (e.g., DOM like tree structures) in the same file as you write JavaScript code, then Babel will transform these expressions into actual JavaScript code. Unlike the past, instead of putting JavaScript into HTML, JSX allows us to put HTML into JavaScript. By using JSX one can write the following JSX/JavaScript code: var nav = ( <ul id="nav"> <li><a href="#">Home</li> <li><a href="#">About <li><a href=”#”>Clients <li><a href=”#”>Contact Us <https://www.onlineinterviewquestions.com/contact-us/> </ul> ); And Babel will transform it into this: var nav = React.createElement( "ul", { id: "nav" }, React.createElement( "li", null, React.createElement( "a", { href: "#" }, "Home" ) ), React.createElement( "li", null, React.createElement( "a", { href: "#" }, "About" ) ), React.createElement( "li", null, React.createElement( "a", { href: "#" }, "Clients" ) ), React.createElement( "li", null, React.createElement( "a", { href: "#" }, "Contact Us" ) ) ); source:https://www.reactenlightenment.com/react-jsx/5.1.html 5. Explain life Cycle of React JS Component ? React JS Component Lifecycle Each component has several “lifecycle methods” that you can override to run code at particular times in the process. Methods prefixed with will are called right before something happens, and methods prefixed with did are called right after something happens. Mounting These methods are called when an instance of a component is being created and inserted into the DOM: - constructor() - componentWillMount() - render() - componentDidMount() Updating An update can be caused by changes to props or state. These methods are called when a component is being re- rendered: - componentWillReceiveProps() - shouldComponentUpdate() - componentWillUpdate() - render() - componentDidUpdate() Unmounting This method is called when a component is being removed from the DOM: - componentWillUnmount() Other APIs Each component also provides some other APIs: - setState() - forceUpdate() Class Properties - defaultProps - displayName Instance Properties - props - state Source: https://facebook.github.io/react/docs/react-component.html 6. List some features of ReactJS? Undoubtedly today React is among of one the best JavaScript UI frameworks. It comes with lot of features that helps programmers to create beautifull application easily, we have list some of them below. - It’s Adaptability - Free and Open Source - Decorators from ES7 - Server-side Communication - Asynchronous Functions & Generators - Flux Library - Destructuring Assignments - Usefulness of JSX Read more from https://www.onlineinterviewquestions.com/react-js-interview-questions/ -- You received this message because you are subscribed to the Google Groups "Swagger" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. For more options, visit https://groups.google.com/d/optout.
