react js-tutorial

React Interview Questions and Answers

Question 1. What is React?

Answer: React is a front-end and open-source JavaScript library which is useful in developing user interfaces specifically for applications with a single page. It is helpful in building complex and reusable user interface(UI) components of mobile and web applications as it follows the component-based approach.

The important features of React are:

  • It supports server-side rendering.
  • It will make use of the virtual DOM rather than real DOM (Data Object Model) as RealDOM manipulations are expensive.
  • It follows unidirectional data binding or data flow.
  • It uses reusable or composable UI components for developing the view.

Question 2. What are the advantages of using React?

Answer: MVC is generally abbreviated as Model View Controller.

  • Use of Virtual DOM to improve efficiency: React uses virtual DOM to render the view. As the name suggests, virtual DOM is a virtual representation of the real DOM. Each time the data changes in a react app, a new virtual DOM gets created. Creating a virtual DOM is much faster than rendering the UI inside the browser. Therefore, with the use of virtual DOM, the efficiency of the app improves.
  • Gentle learning curve: React has a gentle learning curve when compared to frameworks like Angular. Anyone with little knowledge of javascript can start building web applications using React.
  • SEO friendly: React allows developers to develop engaging user interfaces that can be easily navigated in various search engines. It also allows server-side rendering, which boosts the SEO of an app.
  • Reusable components: React uses component-based architecture for developing applications. Components are independent and reusable bits of code. These components can be shared across various applications having similar functionality. The re-use of components increases the pace of development.
  • Huge ecosystem of libraries to choose from: React provides you with the freedom to choose the tools, libraries, and architecture for developing an application based on your requirement.

Question 3. What are the limitations of React?

Answer: The few limitations of React are as given below:

  • React is not a full-blown framework as it is only a library.
  • The components of React are numerous and will take time to fully grasp the benefits of all.
  • It might be difficult for beginner programmers to understand React.
  • Coding might become complex as it will make use of inline templating and JSX.

Question 4. Can web browsers read JSX directly?

Answer: Web browsers cannot read JSX directly. This is because they are built to only read regular JS objects and JSX is not a regular JavaScript object

For a web browser to read a JSX file, the file needs to be transformed into a regular JavaScript object. For this, we use Babel

Question 5. What is JSX?

Answer: JSX is a syntax extension of JavaScript. It is used with React to describe what the user interface should look like. By using JSX, we can write HTML structures in the same file that contains JavaScript code.

Question 6. What is an event in React?

Answer: An event is an action that a user or system may trigger, such as pressing a key, a mouse click, etc. React events are named using camelCase, rather than lowercase in HTML.

With JSX, you pass a function as the event handler, rather than a string in HTML.

Question 7. Why is there a need for using keys in Lists?

Answer: Keys are very important in lists for the following reasons:

  • A key is a unique identifier and it is used to identify which items have changed, been updated or deleted from the lists
  • It also helps to determine which components need to be re-rendered instead of re-rendering all the components every time. Therefore, it increases performance, as only the updated components are re-rendered

Question 8. What are forms in React?

Answer: React employs forms to enable users to interact with web applications.

  • Using forms, users can interact with the application and enter the required information whenever needed. Form contain certain elements, such as text fields, buttons, checkboxes, radio buttons, etc
  • Forms are used for many different tasks such as user authentication, searching, filtering, indexing, etc

Question 9. What is the use of render() in React?

Answer: It is required for each component to have a render() function. This function returns the HTML, which is to be displayed in the component.

If you need to render more than one element, all of the elements must be inside one parent tag like <div>, <form>.

Question 10. What is a state in React?

Answer: The state is a built-in React object that is used to contain data or information about the component. The state in a component can change over time, and whenever it changes, the component re-renders.

The change in state can happen as a response to user action or system-generated events. It determines the behavior of the component and how it will render.

Question 11. What are props in React?

Answer: Props are short for Properties. It is a React built-in object that stores the value of attributes of a tag and works similarly to HTML attributes.

Props provide a way to pass data from one component to another component. Props are passed to the component in the same way as arguments are passed in a function.

Question 12. What is a higher-order component in React?

Answer: A higher-order component acts as a container for other components. This helps to keep components simple and enables re-usability. They are generally used when multiple components have to use a common logic.

Question 13. What is Redux?

Answer: Redux is an open-source, JavaScript library used to manage the application state. React uses Redux to build the user interface. It is a predictable state container for JavaScript applications and is used for the entire application’s state management.

Question 14. What are the components of Redux?

Answer: Components of Redux are:

  • Store: Holds the state of the application.
  • Action: The source information for the store.
  • Reducer: Specifies how the application’s state changes in response to actions sent to the store.

Question 15. Why do we need to React Router?

Answer: Here are some needs of React Router:

  • It maintains consistent structure and behavior and is used to develop single-page web applications.
  • Enables multiple views in a single application by defining multiple routes in the React application.

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