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Interview Preparation Guide

React JS
Questions & Answers

A comprehensive, expert-curated list of real interview questions to help you prepare effectively and land your dream job.

Document Details

Topic / Subject
React JS
Content Length
25 Curated Q&A
Generated On
October 4, 2026
Provided By
SarthiQ.com
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Top React JS Interview Questions

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React JS Interview Questions

Practice with real React JS interview questions

01
A Full Stack Developer was asked
SarthiQ React JS
Hard
Asked in 2026
Q. Describe how you would architect a cloud-native React application using microservices for handling different user roles and permissions.
Ans. To architect a cloud-native React application using microservices for managing different user roles and permissions, you can follow these steps: 1. Microservice Architecture: Define microservices for user management, role management, and a service for the main application logic. Each service can be deployed independently on a cloud platform like AWS or Azure. 2. API Gateway: Use an API Gateway to route requests to the corresponding microservices based on user role. - Example: Using AWS API Gateway or Kong. 3. Authentication and Authorization: Implement a centralized authentication service (e.g., Auth0 or AWS Cognito) to handle user sign-in and issue JWT tokens based on user roles. 4. React Application: Structure your React application to consume these microservices. - Example of a service call:
javascript
import React, { useEffect, useState } from 'react';
import axios from 'axios';

const UserDashboard = () => {
  const [userRole, setUserRole] = useState(null);
  const [data, setData] = useState(null);

  useEffect(() => {
    const fetchRoleData = async () => {
      const token = localStorage.getItem('token');
      const response = await axios.get('/api/user/role', {
        headers: { Authorization: `Bearer ${token}` },
      });
      setUserRole(response.data.role);
    };
    fetchRoleData();
  }, []);

  useEffect(() => {
    if (userRole) {
      const fetchData = async () => {
        const response = await axios.get(`/api/data/${userRole}`);
        setData(response.data);
      };
      fetchData();
    }
  }, [userRole]);

  return <div>{data ? JSON.stringify(data) : 'Loading...'}</div>;
};

export default UserDashboard;
5. Deployment: Use Docker containers for each microservice, and orchestrate them with Kubernetes on your cloud provider to ensure scalability and manageability. This architecture allows for flexible role management, independent service scaling, and improved security through microservices.
Full Stack DeveloperCore Concept
02
A Software Engineer was asked
SarthiQ React JS
Medium
Asked in 2025
Q. Can you explain the React component lifecycle and the role of the virtual DOM?
Ans. The React component lifecycle refers to the different phases that a component goes through: mounting, updating, and unmounting. Each phase has specific lifecycle methods that can be overridden to execute code at particular times. For instance, during the mounting phase, componentDidMount is called after the component is inserted into the DOM:
javascript
class MyComponent extends React.Component {
  componentDidMount() {
    console.log('Component has been mounted!');
  }

  render() {
    return <div>Hello World!</div>;
  }
}
The virtual DOM is a lightweight copy of the actual DOM. When state or props change, React first updates the virtual DOM, then compares it with the actual DOM (a process called reconciliation) to determine the minimal number of updates needed. This optimization leads to improved performance and a smoother user experience.
Software EngineerCore Concept
03
Software Engineer
SarthiQ React JS
Hard

Question:

How would you design a scalable system for XYZ...

04
Software Engineer
SarthiQ React JS
Hard

Question:

How would you design a scalable system for XYZ...