Basic React interview questions

Preparing for a React interview can be a daunting task, especially with the increasing popularity of React in web development. To help you succeed in your interview, we have compiled a list of common React interview questions along with their answers. This comprehensive guide will cover a wide range of topics, from the basics of React to more advanced concepts and best practices. Whether you are a beginner or an experienced React developer, this blog will serve as a valuable resource to enhance your interview preparation.

1. What is React?

React is a popular JavaScript library for building user interfaces. It was developed by Facebook and is widely used for creating interactive and dynamic web applications. React uses a component-based approach, allowing developers to build reusable UI components and efficiently update and render them based on changes in the application's data.

2. What are the key features of React?

The key features of React are:

• Component-Based Architecture: React follows a modular approach, where the UI is divided into reusable components. Each component manages its own state and can be composed together to build complex user interfaces.
• Virtual DOM: React uses a virtual DOM to efficiently update and render components. The virtual DOM is a lightweight copy of the actual DOM, and React compares it with the previous state to determine the minimum number of changes required for updating the UI.
• One-Way Data Binding: React follows a unidirectional data flow, where data is passed from parent components to child components through props. This ensures that the data flow is predictable and helps in maintaining the application's state.
• JSX Syntax: React allows developers to write HTML-like syntax called JSX, which allows them to define the structure and appearance of the UI components directly in JavaScript. JSX combines the power of JavaScript and HTML, making it easy to write and understand.
• React Native: React Native is a framework based on React that allows developers to build native mobile applications for iOS and Android using JavaScript. With React Native, developers can write once and deploy to multiple platforms, saving time and effort in mobile app development.

What are the differences between React and other JavaScript frameworks?

Some key differences between React and other JavaScript frameworks like Angular and Vue.js are:

• Approach to UI Development: React follows a component-based approach, where UI components are reusable and can be composed together. Angular and Vue.js also support component-based development, but they provide a more opinionated framework structure.
• Learning Curve: React has a relatively shallow learning curve compared to Angular, which has a steep learning curve due to its extensive features and concepts. Vue.js falls somewhere in between, offering simplicity and ease of use.
• Community and Ecosystem: React has a large and active community, backed by Facebook. It has a rich ecosystem of libraries, tools, and resources, making it easy to find solutions and support. Angular and Vue.js also have a strong community and growing ecosystems.
• Performance: React's virtual DOM implementation and efficient rendering make it highly performant. Angular and Vue.js also prioritize performance, but React's virtual DOM diffing algorithm gives it an edge in terms of performance optimization.

What are React components?

React components are the building blocks of a React application. They are independent and reusable UI elements that can be combined to create complex user interfaces. Components can have their own state, receive data through props, and render dynamic content based on the data.

There are two types of React components:

1. Function Components: Function components are simple JavaScript functions that accept props as arguments and return JSX to define the component's UI. They are stateless and do not have their own lifecycle methods.
2. Class Components: Class components are ES6 classes that extend the React.Component class. They have their own state, lifecycle methods, and can handle more complex logic. Class components are used when state management or lifecycle methods are required.

What is JSX?

JSX is a syntax extension for JavaScript that allows developers to write HTML-like code within JavaScript. It is a key feature of React and provides a concise and familiar syntax for defining the structure and appearance of UI components.

JSX is not a template language, but a syntax transformation that is transpiled into regular JavaScript by tools like Babel. It allows developers to mix JavaScript expressions and HTML-like syntax, making it easier to understand and maintain the UI code.

What is state in React?

In React, state represents the current condition or data of a component. It is an object that determines how a component behaves and renders. State allows components to be dynamic and responsive to user interactions and changes in data.

State is typically initialized in the constructor of a class component and can be updated using the setState() method. When state changes, React will automatically re-render the component and update the UI accordingly.

What are props in React?

Props (short for properties) are a way to pass data from parent components to child components in React. They allow components to be dynamic and reusable by providing them with external data.

What are lifecycle methods in React?

Lifecycle methods are special functions that are invoked at specific stages of a React component's lifecycle. These methods allow developers to perform actions or implement logic at different points in the component's existence, such as before it is mounted, after it is updated, or before it is unmounted.

Some commonly used lifecycle methods in React are:

• componentDidMount: This method is called immediately after the component is rendered and added to the DOM. It is commonly used for performing API calls, setting up event listeners, or initializing third-party libraries.

• componentDidUpdate: This method is called after the component's updates are reflected in the DOM. It is useful for performing side effects or additional data fetching based on changes in props or state.

• componentWillUnmount: This method is invoked just before the component is unmounted and removed from the DOM. It is commonly used for cleaning up resources, canceling subscriptions, or removing event listeners.

Explain the lifecycle of a React component.

The lifecycle of a React component can be divided into three main phases: Mounting, Updating, and Unmounting.

1. Mounting: The mounting phase occurs when an instance of a component is being created and inserted into the DOM. During this phase, the following methods are called in order:
2. constructor: Initializes the component and sets its initial state.
3. render: Returns the JSX to be rendered.

4. componentDidMount: Performs any necessary setup after the component is mounted.

5. Updating: The updating phase occurs when a component is being re-rendered due to changes in its props or state. During this phase, the following methods are called in order:

6. render: Returns the updated JSX to be rendered.

7. componentDidUpdate: Performs any necessary side effects after the component is updated.

8. Unmounting: The unmounting phase occurs when a component is being removed from the DOM. During this phase, the following method is called:

9. componentWillUnmount: Performs any necessary cleanup before the component is unmounted.

What is the difference between synthetic events and native events in React?

In React, events are implemented as synthetic events, which are a cross-browser wrapper around the browser's native events. Synthetic events provide a consistent interface for handling events across different browsers and platforms.

The main difference between synthetic events and native events is that synthetic events are pooled and reused by React. This means that the event object passed to the event handler is actually a synthetic event object created by React, not the native event object provided by the browser.

Synthetic events have the same properties and methods as native events, but they have some additional features. For example, synthetic events have methods like preventDefault() and stopPropagation() that work consistently across different browsers.

What is React Router?

React Router is a popular library for handling routing in React applications. It provides a declarative way to define the navigation structure of an application and handle URL-based routing.

React Router allows developers to create multiple pages or views within a single-page application and handle navigation between them. It provides components like Router, Route, Link, and Switch that can be used to define the routes and render the appropriate components based on the current URL.

Conclusion

In this blog, we have covered a wide range of interview questions and answers related to React. From the basics of React components and state management to more advanced topics like React Hooks and performance optimization, this comprehensive guide will help you prepare for your React interviews with confidence. Remember to not only memorize the answers but also understand the underlying concepts and best practices. Good luck with your React interviews! As an expert in React development, CronJ React js development India has extensive experience in building high-quality React applications.