React Interview Questions

Hey folks!many of us find it difficult and overwhelming to be prepared for interviews .So here is a list of frequently asked and most important React questions with detailed answers. As a React developer, it’s crucial to be well-prepared for job interviews to showcase your skills and experience effectively. Interviewers may ask a variety of questions to assess your technical knowledge, problem-solving abilities, and understanding of React concepts. In this article, we will explore some common interview questions you may encounter as a React developer and how to best answer them.

What is React and how does it work?

This is a fundamental question that you should be able to answer concisely. React is a popular JavaScript library used for building user interfaces. It allows developers to create reusable UI components that update efficiently when the underlying data changes. React uses a virtual DOM to optimize rendering performance, and it follows a unidirectional data flow pattern, where data flows from parent components to child components through props.

What are the key differences between React class components and functional components?

React class components are ES6 classes that extend the React.Component class and use the render() method to return JSX. They have a state and lifecycle methods, such as componentDidMount() and componentDidUpdate(). On the other hand, functional components are simply JavaScript functions that return JSX. They do not have a state or lifecycle methods, but they can use React hooks, such as useState() and useEffect(), to manage state and handle side effects.

What is JSX in React?

JSX stands for JavaScript XML, and it is a syntax extension for writing XML-like code in JavaScript. It allows developers to write HTML-like code directly in their JavaScript files, which is then compiled to JavaScript by tools like Babel. JSX makes it easier to create and manipulate UI components in React, and it is a key feature that sets React apart from other JavaScript libraries.

What are props in React?

Props (short for properties) are used to pass data from parent components to child components in React. They are read-only and immutable, meaning that child components cannot modify the values of props received from their parent components. Props allow for communication between components and enable the building of reusable and modular UI components.

What are React Hooks?

React Hooks are functions that allow developers to use state and other React features in functional components without needing to use class components. Some commonly used hooks are useState(), useEffect(), and useContext(). For example, useState() allows functional components to have local state, and useEffect() lets them handle side effects, such as fetching data or updating the DOM, in a declarative way.

How does React handle component lifecycle?

React has a set of lifecycle methods that are called at different stages of a component’s lifecycle. However, with the introduction of functional components and hooks, the use of lifecycle methods has become less common. The componentDidMount() and componentDidUpdate() methods, for example, are now replaced with the useEffect() hook. It's essential to be familiar with both class component lifecycle methods and hooks and understand when to use each in your code.

What is the purpose of a key prop in React lists?

The key prop is used in React lists to provide a unique identifier for each item in the list. It helps React identify which items have changed, been added, or been removed from the list when the list is updated. Using a key prop can significantly improve the performance of list rendering and prevent issues with component reusability.

How do you handle forms in React?

Handling forms in React involves capturing user input and managing form data. You can use controlled components, where the form fields are tied to a component’s state, and you handle updates via onChange events. Alternatively, you can use uncontrolled components and access form data using the DOM. You should also validate form data to ensure it meets the required criteria before submitting it to the server.

Here are some best practices for handling forms in React:

Use controlled components:

Controlled components are components that manage the form state in their own state and update the UI with the latest form data. This involves using event handlers like onChange to capture user input and updating the component's state accordingly.

Example of a controlled component:

import React, { useState } from 'react';
const LoginForm = () => {
  const [email, setEmail] = useState('');
  const [password, setPassword] = useState('');
  const handleEmailChange = (event) => {
    setEmail(event.target.value);
  };
  const handlePasswordChange = (event) => {
    setPassword(event.target.value);
  };
  const handleSubmit = (event) => {
    event.preventDefault();
    // Submit form data to the server
  };
  return (
    <form onSubmit={handleSubmit}>
      <input type="email" value={email} onChange={handleEmailChange} />
      <input type="password" value={password} onChange={handlePasswordChange} />
      <button type="submit">Login</button>
    </form>
  );
};
export default LoginForm;

Use form validation:

Validate form data to ensure it meets the expected criteria before submitting it to the server. You can use built-in HTML5 validation attributes like required, minLength, maxLength, etc., or implement custom validation logic in your React components.

Example of form validation using HTML5 attributes:

<input type="text" required minLength="3" maxLength="10" />

Handle form submission:

Use event handlers like onSubmit to capture the form submission event and handle the form data accordingly. Prevent the default form submission behavior using event.preventDefault() to prevent page refresh and handle the form submission in your React component.

Example of handling form submission:

const handleSubmit = (event) => {
  event.preventDefault();
  // Validate form data
  // Submit form data to the server
};

Use form libraries:

There are several form libraries available for React, such as Formik, Redux Form, and React Hook Form, that provide advanced form handling capabilities like form validation, form state management, and form submission handling. These libraries can help simplify form handling in your React applications.

Test form handling:

Write unit tests to ensure that your form handling logic is working correctly. Use testing frameworks like Jest and Enzyme to write tests for your React components that handle forms, and test for different scenarios, including valid and invalid form submissions.

In conclusion, handling forms in React involves capturing user input, managing form state, validating form data, handling form submission, and testing the form handling logic. By using controlled components, implementing form validation, handling form submission, and leveraging form libraries, you can effectively handle forms in your React applications.