Nodejs Interview Questions

Advanced Node.js Questions

41. What is microservices architecture in Node.js?
    • Microservices architecture involves breaking down an application into smaller, independent services that communicate with each other over HTTP or messaging protocols.
42. How do you handle large file uploads in Node.js?
    • Use streams to handle large file uploads without overwhelming the memory, or use third-party libraries like multer for handling multipart form data.
43. What is PM2 in Node.js?
    • PM2 is a production process manager for Node.js applications that allows you to keep your applications alive, auto-restart on failure, and manage log files.
44. What is Rate Limiting and how do you implement it in Node.js?
    • Rate limiting controls the number of requests a client can make to an API in a given time period. It can be implemented using middleware like express-rate-limit.
45. What is load balancing and how can it be achieved in Node.js?
    • Load balancing distributes incoming network traffic across multiple servers. It can be achieved using the cluster module or external tools like Nginx.
46. What is message queueing in Node.js?
    • Message queueing involves sending and receiving messages between services or processes in a reliable and asynchronous manner. Tools like RabbitMQ or Apache Kafka can be used for this purpose.
47. What is OAuth and how do you implement it in Node.js?
    • OAuth is an authorization framework that allows third-party applications to access a user’s resources without exposing their credentials. It can be implemented using packages like passport.
48. How do you perform input validation in Node.js?
    • Input validation can be performed using middleware like express-validator or libraries like joi to ensure the data conforms to expected formats and constraints.
49. What is GraphQL and how does it differ from REST?
    • GraphQL is a query language for APIs that allows clients to request exactly the data they need. Unlike REST, which exposes multiple endpoints for different resources, GraphQL exposes a single endpoint and allows more flexible queries.
50. How do you implement a RESTful API in Node.js?
    • By using Express.js to define routes that correspond to CRUD operations, and using controllers to handle the logic for each endpoint.
51. What is async/await in Node.js?
    • async/await are syntactic features that simplify working with asynchronous code by allowing you to write code that looks synchronous but handles asynchronous operations.
52. How do you manage environment variables in Node.js?
    • Environment variables can be managed using the dotenv package, which loads variables from a .env file into process.env.
53. What is gRPC and how is it used in Node.js?
    • gRPC is a high-performance, open-source RPC framework developed by Google. It uses Protocol Buffers (protobuf) to serialize data and supports multiple languages, including Node.js.
54. What is the event-driven architecture in Node.js?
    • An event-driven architecture is a software design pattern where the flow of the program is determined by events. In Node.js, this is often implemented using EventEmitter.
55. How do you prevent SQL injection in Node.js?
    • By using parameterized queries or ORM libraries like Sequelize that automatically escape user inputs.
56. What is TypeScript and how is it used with Node.js?
    • TypeScript is a typed superset of JavaScript that compiles to plain JavaScript. It adds static typing, which helps catch errors at compile time. It can be used with Node.js to build more reliable applications.
57. What is the purpose of Object Relational Mapping (ORM) in Node.js?
    • ORM allows developers to interact with databases using object-oriented syntax, reducing the need for writing raw SQL queries. Examples include Sequelize and TypeORM.
58. How do you implement WebSockets in Node.js?
    • WebSockets can be implemented using the ws package or Socket.io to enable real-time communication between the client and server.
59. What is the callback hell and how can you avoid it?
    • Callback hell refers to deeply nested callbacks that make code difficult to read and maintain. It can be avoided using promises, async/await, or modularizing code into smaller functions.
60. What is REST and how does it relate to HTTP methods?
    • REST (Representational State Transfer) is an architectural style that uses standard HTTP methods like GET, POST, PUT, DELETE to perform CRUD operations on resources.

Node.js Security Questions

61. How do you handle authentication in a Node.js application?
    • Authentication can be handled using libraries like passport for traditional username/password authentication or JWT for token-based authentication.
62. What is Cross-Site Scripting (XSS) and how do you prevent it in Node.js?
    • XSS is a security vulnerability that allows attackers to inject malicious scripts into web pages. It can be prevented by sanitizing user inputs and using security headers.
63. What is Cross-Site Request Forgery (CSRF) and how do you prevent it in Node.js?
    • CSRF is a vulnerability that tricks users into performing actions they didn’t intend. It can be prevented using anti-CSRF tokens or middleware like csurf.
64. How do you handle data encryption in Node.js?
    • Data encryption can be handled using the crypto module, which provides cryptographic functionality, including a set of wrappers for OpenSSL’s hash, HMAC, cipher, decipher, sign, and verify functions.
65. What is rate limiting and why is it important in Node.js?
    • Rate limiting restricts the number of requests a user can make in a specific time frame, helping to prevent abuse or DDoS attacks. It can be implemented using middleware like express-rate-limit.
66. What are some common security best practices in Node.js?
    • Use HTTPS, validate and sanitize inputs, store secrets securely, keep dependencies updated, and avoid using eval().
67. What is the helmet module and how does it help with security?
    • helmet is a Node.js middleware that helps secure your application by setting various HTTP headers.
68. How do you protect against SQL Injection in Node.js?
    • Use parameterized queries or ORM libraries to prevent user input from being interpreted as SQL code.
69. What is directory traversal and how do you prevent it in Node.js?
    • Directory traversal is a security vulnerability that allows attackers to access files and directories stored outside the web root folder. It can be prevented by validating and sanitizing user input and avoiding unsafe file path concatenation.
70. What is Content Security Policy (CSP) and how do you implement it in Node.js?
    • CSP is a security measure that helps prevent XSS attacks by specifying which content sources are trusted. It can be implemented using the helmet middleware.

Node.js Testing and Debugging Questions

71. What is the mocha testing framework in Node.js?
    • mocha is a JavaScript test framework for Node.js programs that allows asynchronous testing, making it flexible and simple.
72. How do you perform unit testing in Node.js?
    • Unit testing in Node.js can be performed using frameworks like mocha, jest, or jasmine. These frameworks provide tools to write and run tests that ensure individual parts of your code work as expected.
73. What is the chai library in Node.js?
    • chai is an assertion library that works with testing frameworks like mocha to provide human-readable assertions for your tests.
74. What is supertest in Node.js?
    • supertest is a library used for testing HTTP requests in Node.js, often used with mocha and chai to test API endpoints.
75. How do you debug a Node.js application?
    • Debugging can be done using the built-in node inspect command, or by using tools like nodemon, Visual Studio Code’s debugger, or Chrome DevTools.
76. What is jest in Node.js?
    • jest is a JavaScript testing framework developed by Facebook that works well with Node.js applications, providing a robust and user-friendly way to test your code.
77. How do you test asynchronous code in Node.js?
    • Asynchronous code can be tested using callbacks, promises, or async/await within your test cases, depending on the testing framework.
78. What is the difference between describe, it, and beforeEach in Mocha?
    • describe is used to group related tests, it defines individual test cases, and beforeEach runs a function before each test case within a describe block.
79. What is a mock or stub in testing?
    • Mocks and stubs are used to simulate the behavior of real objects or functions to isolate the code being tested. Mocks often come with built-in assertions to check that certain methods were called.
80. How do you handle test coverage in Node.js?
    • Test coverage can be handled using tools like nyc or jest, which track how much of your code is covered by your tests.

Node.js Performance Optimization Questions

81. What is load balancing and how can you implement it in a Node.js application?
    • Load balancing distributes incoming network traffic across multiple servers. It can be implemented using the cluster module or external tools like Nginx.
82. How do you optimize performance in a Node.js application?
    • Performance can be optimized by using asynchronous functions, caching, load balancing, and minimizing the use of blocking code.
83. What is clustering in Node.js and how does it improve performance?
    • Clustering is the process of creating multiple child processes that share the same server port to handle more requests simultaneously, thus improving performance.
84. How do you implement caching in Node.js?
    • Caching can be implemented using in-memory stores like Redis or by caching responses at various levels (e.g., CDN, application, database).
85. What are some techniques to reduce latency in a Node.js application?
    • Techniques include using CDN, optimizing database queries, minimizing payload sizes, and using efficient algorithms.
86. How does lazy loading help improve performance in Node.js?
    • Lazy loading delays the initialization of an object until it’s needed, reducing the initial load time and improving performance.
87. What is event-driven architecture and how does it benefit Node.js?
    • Event-driven architecture allows non-blocking I/O operations, enabling Node.js to handle a large number of concurrent connections efficiently.
88. How do you prevent memory leaks in a Node.js application?
    • Prevent memory leaks by avoiding global variables, properly managing event listeners, using weak references, and regularly profiling the application.
89. What are some common performance bottlenecks in Node.js?
    • Common bottlenecks include synchronous code, heavy computation on the main thread, inefficient database queries, and large payloads.
90. How do you measure and monitor the performance of a Node.js application?
    • Performance can be measured using profiling tools like Node.js Performance Monitoring, New Relic, Prometheus, or APM tools to monitor metrics like response time, memory usage, and throughput.

Node.js Deployment and DevOps Questions

91. How do you deploy a Node.js application?
    • A Node.js application can be deployed on various platforms like AWS, Heroku, DigitalOcean, or using containerization tools like Docker.
92. What is Docker and how is it used with Node.js?
    • Docker is a platform that uses containerization to package an application and its dependencies into a single container. It ensures consistency across multiple environments.
93. What is CI/CD and how is it implemented with Node.js?
    • CI/CD (Continuous Integration/Continuous Deployment) automates the testing and deployment process. Tools like Jenkins, CircleCI, and GitHub Actions are used to implement CI/CD with Node.js.
94. How do you handle environment variables in production Node.js applications?
    • Environment variables can be managed using the dotenv package or directly through environment configuration in deployment platforms like Heroku, AWS, or Docker.
95. What is reverse proxy and how is it used with Node.js?
    • A reverse proxy is a server that forwards client requests to backend servers. Nginx is commonly used as a reverse proxy with Node.js to handle load balancing, SSL termination, and caching.
96. How do you manage multiple versions of Node.js in your environment?
    • Multiple versions of Node.js can be managed using tools like nvm (Node Version Manager).
97. What is the 12-factor app methodology and how does it apply to Node.js applications?
    • The 12-factor app methodology is a set of best practices for building modern web applications that are scalable and maintainable. It applies to Node.js by emphasizing practices like strict separation of configuration from code, stateless processes, and dependency management.
98. How do you scale a Node.js application?
    • Scaling can be achieved by using clustering, load balancing, microservices, containerization, and scaling infrastructure horizontally using cloud services.
99. What is blue-green deployment and how is it implemented in Node.js?
    • Blue-green deployment is a strategy to reduce downtime by running two identical production environments. At any time, only one (blue or green) is live, while the other is used for testing or updates.
100. How do you automate deployment in Node.js? – Deployment automation can be achieved using CI/CD pipelines, containerization tools like Docker, and orchestration platforms like Kubernetes.