Tenmiles – React JS Interview Questions

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

1. What is ReactJS?

React is a open-source, free front-end JavaScript library for building user interfaces or UI components which is maintained by Facebook. React can be used in the development of single-page or mobile applications

2. List some advantages of ReactJS ?

Advantage of React JS

Easy to Learn and Use.
Creating Dynamic Web Applications Becomes Easier.
Reusable Components and SEO Friendly.
Performance Enhancement with support of Handy Tools.
JavaScript Library and the scope for testing the Codes.

3. What are Components in ReactJS ?

A Component is one of the core building blocks of React which return a piece of JSX code that tells what should be rendered on the screen. There are two main types of components are: Class, Functional Components.

4. What is JSX?

JSX stands for JavaScript XML that enables you to write HTML in React. Instead of separating the markup and logic in separated files, React uses components for this purpose.

5. Explain life Cycle of React JS 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. There are four different phases of the React JS components lifecycle: Initialization, Mounting, Updating, and Unmounting.

6. List some features of ReactJS ?

Virtual DOM and JSX.
One-way data binding.
React native and declarative UI.
Component-based architecture.
Speed, efficiency and flexibility.

7. How to use Events in ReactJS ?

React has its own event handling system which is very similar to handling events on DOM elements. The react event handling system is known as Synthetic Events. The synthetic event is a cross-browser wrapper of the browser's native event.

8. What is flux in JavaScript?

Flux is an architecture that Facebook uses internally when working with React. It is not a framework or a library. It is simply a new kind of architecture that complements React and the concept of Unidirectional Data Flow

9. What are refs in ReactJs ? When to use it.

Refs provide a way to access DOM nodes or React elements created in the render method. In the typical React dataflow, props are the only way that parent components interact with their children. To modify a child, you re-render it with new props. They are used in cases where we want to change the value of a child component, without making use of props and all.

10. What are stateless components in ReactJS?

Stateless components are those components which don't have any state at all, which means you can't use this. setState inside these components. It is like a normal function with no render method. It has no lifecycle, so it is not possible to use lifecycle methods such as componentDidMount and other hooks.

11. What is the difference between State and props in React Js ?

In a React component, props are variables passed to it by its parent component. State on the other hand is still variables, but directly initialized and managed by the component. The state can be initialized by props.

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12. What are Synthetic events?

A synthetic event is a cross-browser wrapper around the browser's native event. It has the same interface as the browser's native event, including stopPropagation() and preventDefault() , except the events work identically across all browsers. It achieves high performance by automatically using event delegation.

13. What is the difference between Dom and virtual Dom in ReactJS ?

In React, for every DOM object, there is a corresponding “virtual DOM object.” A virtual DOM object is a representation of a DOM object, like a lightweight copy. 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.

14. Enlist the advantages and disadvantages of ReactJS ?

Advantages of React JS

React JS facilitates the overall process of writing components which boosts productivity and facilitates further maintenance.
It ensures faster rendering with stable code.
It is SEO friendly which comes with a helpful developer toolset.

Disadvantages of React JS

The high pace of development.
Poor Documentation and View Part.
Covers only the UI Layers of the app and nothing else.
JSX as a barrier

15. What are the controlled components and uncontrolled components in ReactJS?

Controlled component is component which gets the changed value from the callback function and uncontrolled component is component that has the one from the DOM. For example, when input value is changed, we can use onChange function in Controlled Component and also we can get the value using DOM like ref.

16. Explain the difference between functional and class components.

A functional component is just a plain JavaScript function that accepts props as an argument and returns a React element. A class component requires you to extend from React. React lifecycle methods can be used inside class components (for example, componentDidMount).

17. What do you understand by mixin or higher order components in ReactJs?

A higher-order component (HOC) is advanced techniques in React for reusing component logic.They are a pattern that emerges from React's compositional nature. Concretely, a higher-order component is a function that takes a component and returns a new component.

18. How is flux different from redux?

The primary difference of Flux vs Redux is that Flux includes multiple Stores per app, but Redux includes a single Store per app. Rather than placing state information in multiple Stores across the application, Redux keeps everything in one region of the app. This causes an issue in application management.

19. How is ReactJS different from angular and VUE js?

Angular uses TypeScript and splits HTML + TypeScript logic apart, React uses JavaScript and a feature called “JSX” (it combines “HTML” and JavaScript logic), Vue uses regular JavaScript and splits HTML + JavaScript logic apart.

20. What is the use of arrow function in ReactJS?

The arrow function is used to write functions in a more concise syntax. They were introduced in ES6. They also allow you to bind the context of the components as binding is available by default in ES6.

21. What are refs in ReactJS?

Refs are a function that acts as a way to reference a DOM element or a class component from within a parent component. It enables to read and modify the value of a child component, without making use of props. Refs can be helpful when using third party libraries as well in animations.

22. What is the purpose of render() function in ReactJS?

The render() function displays the specified HTML code inside the specified HTML element. Each React component must have a render(). This function takes 2 arguments, namely HTML code and an HTML element, and returns a single element.

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