7. 21 essential React.js interview questions and answers

React is an open-sourced facility provided by JavaScript where one can use the library to code for the front end. Available as website, mobile as well as desktop applications, React is managed by Facebook in collaboration with some other independent firms and developers. React.js consists of a user interface which in turn consists of components. The React.js demand is increasing day by day and thus the competition. The below questions will help in preparation for the React interview. Moreover, these sets will guide you through the path of getting proper knowledge on some terms of the same.
1Q. What is React?
A. A Facebook-owned JavaScript library that consists of a user interface in turn consisting of reusable UI components and elements. These can be used for front end coding for several applications and software development. It is an open-source library.
2Q. Mention the prominent features of React.

1. The features of React include the following:-

• The utilization of a Virtual DOM instead of a real DOM.
• The rendering style of React is server sided.
• The data binding or data flow of React is unidirectional.
  3Q. Can you count some of the limitations of React?

1. React cannot be treated as a fully-fledged framework for JavaScript or coding.
   The elements, components and navigation in the user interface are not the cup of tea for beginners and takes a bit of practice to master or at least understand.
   The library is too vast and to locate specific tools for one’s use requires a bit of experience as well as some hard-earned knowledge, tricks and tools.
   The utilization of JSX and inline templating makes coding to React a tad bit more difficult in comparison to other such tools.
   4Q. What exactly is meant by the JSX?
2. JSX is nothing but the acronym of JavaScript XML. It’s a file that is utilized by React in order to make HTML easier, along with the expressiveness of JavaScript Online Training
3. and HTML template syntax.
   5Q. Define Virtual DOM.
4. It is a JavaScript object that is a clone of the real DOM used for listing elements, objects, attributes and properties. The changes made to them reflect accordingly. But the difference is that only the final changes reflect after saving and not the intermediate ones, unlike a real DOM.
   6Q. Why are JSX unreadable by browsers?
5. Because they are not proper JavaScript objects and need transformation into one.
   7Q. Differentiate between Angular and React.
6. While React has server-side rendering and uses virtual DOM, Angular has client-side rendering and uses real DOM.
   8Q. Explain the statement that Everything is a component in React.
7. Every UI is split into packages of components. Thus Everything on React is just a component.
   9Q. Describe the purpose of render().
8. It is used to return a single representative value of the native DOM component.
   10Q. Define Props.
9. Props are the properties of objects stored in React.
   11Q. Why Arrow is used?
10. These are used as syntax(=>).
    12Q. Mention different phases of React component’s lifecycle.
11. Initial rendering, updating and unmounting phases.
    13Q. Name some lifecycle methods.
12. ComponentDidMount(), shouldComponentUpdate(), componentDidUpdate(), etc.
    14Q. Define a React event.
13. A reaction triggered by manual actions like the keypress, click, etc., is known as an event.
    15Q. Define symbolic event.
14. A cross-browser wrapper around the native event of a browser.
    16Q. How can a code be modularized?
15. By using export and import properties.
    17Q. Differentiate between controlled and uncontrolled components.
16. Former does not maintain state and are controlled by the parent component. Latter maintain state and are controlled by DOM.
    18Q. Define HOC.
17. High Order Components are customized components used for wrapping another one to reuse component logic.
    19Q. Uses of HOC
18. Render high jacking, manipulation of props, code reuse, etc.
    20Q. Why keys are used?
19. Various virtual DOM elements are identified through unique keys.
    21Q. Mention 3 principles of Redux.
20. The state is read-only, a single source of truth and changes are made with pure functions.
    React interview is neither everyone’s cup of tea nor an uphill task. The above questions will take the preparation of an aspirant a step further towards achieving their goal.