Master Essential React JS Questions for Interviews in 2022

React JS is a popular JavaScript library for building user interfaces, and it's in high demand among employers. If you're preparing for a React JS interview, you'll want to master these essential questions to increase your chances of success in 2022.

Table of Contents

  1. What is React JS?
  2. What are React components?
  3. What are JSX and its benefits?
  4. What are the differences between class components and functional components?
  5. What is React state?
  6. What are React props?
  7. What is the virtual DOM?
  8. What are lifecycle methods in React?
  9. What are hooks in React?
  10. What is Redux and why is it used with React?

What is React JS?

React JS is an open-source JavaScript library, developed and maintained by Facebook, that's used for building fast and interactive user interfaces. It's based on a component-based architecture, which allows developers to create reusable UI components and manage their state efficiently.

What are React components?

React components are individual, reusable pieces of the UI that manage their state and render output. They can be either class-based or function-based components. Components can be nested and composed to create complex UI structures.

What are JSX and its benefits?

JSX (JavaScript XML) is a syntax extension for JavaScript that allows developers to write HTML-like code within their JavaScript code. It's used in React to define the structure and appearance of the UI components. The benefits of using JSX include:

  • Improved code readability
  • Easier to write and maintain
  • Compile-time error checking
  • Enables the use of JavaScript expressions within the markup

Class Components vs. Functional Components

Class components are created using ES6 classes and extend the React.Component class. They can have state and lifecycle methods. Functional components, on the other hand, are simple JavaScript functions that accept props as an argument and return JSX.

The differences between the two include:

  • Class components can have state, while functional components are stateless (before hooks were introduced)
  • Class components have lifecycle methods, while functional components do not (before hooks)
  • Functional components are typically shorter and more readable
  • Functional components can use hooks to manage state and lifecycle features

What is React state?

State in React is an object that represents the dynamic data of a component. It can change over time, and when it does, React automatically re-renders the component to reflect those changes. State is managed within a component and cannot be accessed directly by other components unless passed through props.

What are React props?

Props (short for properties) in React are used to pass data from a parent component to a child component. They are read-only, which means that a child component cannot modify the props it receives. Props help to create reusable and configurable components.

What is the virtual DOM?

The virtual DOM is a lightweight in-memory representation of the actual DOM. React uses the virtual DOM to track changes to the UI and perform efficient updates to the actual DOM. When a component's state or props change, React creates a new virtual DOM and calculates the difference between the new and old virtual DOMs. This process, called "reconciliation," allows React to make minimal updates to the actual DOM, improving performance.

What are lifecycle methods in React?

Lifecycle methods in React are special methods that are called at specific points during a component's life, such as when it's created, updated, or destroyed. They allow developers to control the behavior of a component, manage state, and perform side effects like fetching data or updating the DOM. Some common lifecycle methods include:

  • componentDidMount: called after the component is rendered to the DOM
  • componentDidUpdate: called after the component is updated (state or props change)
  • componentWillUnmount: called immediately before the component is removed from the DOM

What are hooks in React?

Hooks are a set of functions introduced in React 16.8 that allow developers to use state and lifecycle features in functional components. They provide a simpler and more concise way to manage state and side effects compared to class components. Some commonly used hooks include:

  • useState: manages component state in functional components
  • useEffect: performs side effects in functional components, similar to lifecycle methods in class components
  • useContext: provides access to the React context in functional components

What is Redux and why is it used with React?

Redux is a standalone state management library often used in combination with React. It helps to manage the application's state in a more predictable and centralized way. Redux is particularly useful for large-scale applications with complex state management requirements.


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