Crux – React JS Interview Questions

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

1. Which is the return statement in React?

The render method returns a description of what the DOM should look like, and then react efficiently updates the real DOM to match. Render is that what exactly want to trigger multiple times. Return is that which you want to Display.

2. How to keep a representation of UI part?

Even though React does not require JSX, it is the recommended way of describing our UI in React app. all React DOM functionality was part of React .Also, to enable our component to have direct access to our store and thus.

3. Different types of DOM?

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. Manipulating the DOM is slow. Manipulating the virtual DOM is much faster, because nothing gets drawn onscreen.

4. How to find the area of suitability in React?

React is the most-used JavaScript UI library for creating modern applications in the world. What makes React shine and different from other frameworks is the powerful features and concepts that React introduced, such as JSX, virtual DOM, components, etc.

5. Which function is used to create UI representation?

The UI Framework is the set of classes and interfaces that define the elements and behavior of a window-based UI Subsystem. It defines a structure for defining user interfaces.

6. What are the different phases of component lifecycle?

The different phases of component lifecycle are initialization, Mounting, Updating, and Unmounting.

7. What are Higher-Order Components?

Higher Order Component (HOC) is wrapping around "normal" component and provides additional data input. It is actually a function that takes one component and returns another component that wraps the original one

8. What are the controlled components?

A Controlled Component is one that takes its current value through props and notifies changes through callbacks like onChange . A parent component "controls" it by handling the callback and managing its own state and passing the new values as props to the controlled component.

9. What are uncontrolled components?

A Uncontrolled Component is one that stores its own state internally, and you query the DOM using a ref to find its current value when you need it. This is a bit more like traditional HTML.

10. What is the purpose of using super constructor with props argument?

The constructor for a React component is called before it is mounted. When implementing the constructor for a React. Component subclass, you should call super (props) before any other statement. Props will be undefined in the constructor, which can lead to bugs.

11. What is reconciliation?

Reconciliation is the process through which React updates the DOM. When a component's state changes, react has to calculate that if it is necessary to update the DOM. It does this by creating a virtual DOM and comparing it with the current DOM. In this context, the virtual DOM will contain the new state of the component.

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12. Why React uses class Name over class attribute?

Class is a keyword in JavaScript and JSX is an extension of JavaScript. That's the principal reason why React uses className instead of class. See JavaScript Keywords + Reserved Words. The fact that a token is a keyword means that we cannot use it in some expressions.

13. What are fragments?

A common pattern in React is for a component to return multiple elements. Fragments let you group a list of children without adding extra nodes to the DOM.

14. What are portals in React?

Portals provide a first-class way to render children into a DOM node that exists outside the DOM hierarchy of the parent component. The first argument ( child ) is any renderable React child, such as an element, string, or fragment.

15. What are stateless components?

Stateless components declared as a function that has no state and returns the same markup given the same props. A quote from the React documentation: These components must not retain internal state, do not have backing instances, and do not have the component lifecycle methods.

16. What are stateful components?

A stateful component also referred to as a smart component keeps track of changes to the data in a javascript object called a state. A stateless component also known as a dumb component just renders what is given to it by a javascript object called props without keeping track of changes.

17. What is the use of react-dom package?

ReactDOM is a package that provides DOM specific methods that can be used at the top level of a web app to enable an efficient way of managing DOM elements of the web page. ReactDOM provides the developers with an API containing the following methods and a few more.

18. What is React DOM Server

ReactDOMServer. renderToString(element) Render a React element to its initial HTML. React will return an HTML string. You can use this method to generate HTML on the server and send the markup down on the initial request for faster page loads and to allow search engines to crawl your pages for SEO purposes.

19. What will happen if you use set State() in constructor?

setState" causes React to re-render your application and update the DOM. you can also track of prevstate in setState If you use setState in constructor you would get error like this:Can only update a mounted or mounting component. This usually means you called setState() on an unmounted component.

20. What will happen if you use props in initial state?

Using props to generate state in getInitialState often leads to duplication of “source of truth”, i.e. where the real data is. This is because getInitialState is only invoked when the component is first created.

21. What is the lifecycle methods order in mounting?

React has four built-in methods that gets called, in this order, when mounting a component: constructor() getDerivedStateFromProps() render()

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Crux React JS Interview Questions