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Top 100 Node Js Interview Questions and Answers for 2024

Published: 27th June, 2023
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Arunav Goswami

Web Development Consultant at almaBetter

Elevate your preparation with our extensive guide on 'Node.js interview questions'. This resource features 100 crucial questions, from basics to advanced level.

Embarking on your journey in the Node.js universe, whether as a fresher or an experienced professional, can be thrilling, yet a tad bit daunting. The path towards acing that interview often winds through the most fundamental concepts to the most intricate facets of this extensive ecosystem. The array of questions that can arise may leave you pondering where to direct your preparation efforts. However, rest assured, we've designed a resource that's got you covered!

Welcome to our meticulously curated guide on 'Node.js interview questions'. This comprehensive treasure trove has been crafted to cater to everyone, from beginners grappling with 'Node.js interview questions for freshers' to seasoned developers wrestling with 'Node.js interview questions for experienced'. We've compiled a list of 100 key questions that traverse the breadth and depth of Node.js, beginning with the basics and escalating to cover the advanced aspects.

Q.1. Where is Node.js used?

Solution: Node.js is employed across diverse domains, earning high esteem, particularly in the realm of:

  • Network applications
  • Distributed computing
  • Responsive web applications
  • Server-client applications

Q.2. Why is Node.js single-threaded?

Solution: By operating on a single-threaded model, Node.js guarantees support for asynchronous processing. This unique approach enhances scalability and efficiency, enabling applications to deliver exceptional performance and effectiveness even when subjected to heavy loads.

Q.3. What are the different API functions supported by Node.js?

Solution: Two distinct categories of API functions exist, each serving a specific purpose:

  • Synchronous APIs: These are employed for non-blocking functions, enabling smooth execution without causing delays or interruptions.
  • Asynchronous APIs: These are utilized for blocking functions, facilitating the handling of tasks that require waiting for a response or completion before proceeding.

Q.4. What is the control flow function?

Solution: In Node.js, control flow functions play a vital role in managing the execution order of asynchronous function calls. These code snippets are commonly utilized to determine the sequence in which these functions are evaluated whenever they are invoked.

Q.5. Why is Node.js so popular these days?

Solution: Node.js has garnered significant popularity due to its predominant use of JavaScript, offering programmers a wide range of possibilities, including:

  • Server-side JavaScript: It enables developers to write JavaScript code that runs on the server, expanding the language's capabilities beyond just browser-based applications.
  • Access to the HTTP stack: Node.js provides convenient access to the HTTP stack, allowing programmers to handle web requests and responses effectively.
  • File I/O entities: It offers streamlined file input/output operations, enabling seamless handling of file-related tasks.
  • Support for TCP and other protocols: Node.js facilitates the development of network applications by providing support for TCP and various other protocols.
  • Direct database access: It grants direct access to databases, empowering developers to interact with databases efficiently and effortlessly.

Q.6. What is an event loop in Node.js?

Solution: When running an application in Node.js, the handling of callbacks is essential. To accomplish this, Node.js employs event loops, which play a crucial role due to its support for non-blocking communication.

The event loop operates by initiating callbacks whenever an event is triggered, often through a dedicated listener. After calling these functions, Node.js continues executing the code without waiting for the outputs to be obtained immediately.

Once all the code has been executed, the outputs are retrieved, and the callback function is invoked. This process operates in a continuous loop, aptly named the event loop, ensuring efficient handling of callbacks throughout the application's execution.

Q.7. What are the asynchronous tasks that should occur in an event loop?

Solution: The event loop in Node.js enables the execution of several tasks asynchronously, including:

  • Handling Blocking Send Requests: Node.js efficiently manages to block send requests by executing them asynchronously, allowing other operations to proceed without being blocked.
  • High Computational Requirements: Node.js effectively handles tasks with high computational demands by executing them asynchronously, ensuring that the event loop remains responsive and other operations are not hindered.
  • Real-time I/O Operations: The event loop in Node.js is well-suited for real-time input/output (I/O) operations. It enables the seamless handling of real-time data streams, ensuring timely processing and responsiveness.

Q.8. What is the order of execution in control flow statements?

Solution: The processing of function calls in Node.js follows a specific sequence, governed by control flow statements. This order typically includes the following steps:

  • Execution and Queue Handling: The control flow statements manage the execution of function calls and handle the queue of pending tasks.
  • Data Collection and Storage: As the function calls are processed, data is collected and stored, ensuring efficient handling and manipulation of information.
  • Concurrency Handling and Limiting: Control flow statements are responsible for managing concurrency, and controlling the number of simultaneous tasks being executed to prevent overwhelming the system.
  • Execution of the Next Piece of Code: Once the necessary tasks have been completed, the control flow statements facilitate the execution of the next segment of code in the application's flow, ensuring a smooth progression of operations.

Q.9. Are there any disadvantages to using Node.js?

Solution: In scenarios where intensive CPU computations are involved, a multi-threaded platform can deliver enhanced performance and responsiveness. However, it is worth noting that the usage of relational databases with Node.js is gradually becoming less prevalent and may be considered outdated.

Q.10. What is the primary reason to use the event-based model in Node.js?

Solution: The event-based model in Node.js serves as a solution to address the challenges that arise when employing blocking operations in the I/O channel.

Moving forward in this blog focused on Node.js inquiries, it is important to explore the process of importing libraries into Node.js.

Q.11. What are the security implementations that are present in Node.js?

Solution:  There are essential implementations that play a significant role in ensuring security:

  • Error Handling Protocols: Implementing robust error handling protocols helps in identifying and mitigating security vulnerabilities. Proper handling and reporting of errors can prevent sensitive information from being exposed and enhance the overall security of the application.
  • Authentication Pipelines: Establishing secure authentication pipelines is crucial for verifying the identity and access rights of users. Proper implementation of authentication protocols, such as multi-factor authentication and secure session management, helps protect against unauthorized access and bolster the security of the system.

Q.12. What is the meaning of a test pyramid?

Solution: The test pyramid methodology represents the distribution of test cases across different levels of testing, namely unit testing, integration testing, and end-to-end testing. It emphasizes executing a higher number of test cases at the unit testing level, followed by integration testing, and finally fewer test cases at the end-to-end testing level. This approach ensures comprehensive test coverage throughout the development lifecycle of a project.

Q.13. Why does Google use the V8 engine for Node.js?

Solution: Google employs the V8 engine due to its ability to seamlessly convert JavaScript code into a low-level language. This conversion process enables the execution of applications with exceptional performance. Additionally, it empowers users to interact with the application in real time, ensuring a smooth and responsive user experience.

Q.14. What is the difference between spawn and fork methods in Node.js?

Solution: The spawn() function in Node.js serves the purpose of creating and launching a new process using the command line. It generates a node module within the processor, which is invoked by Node.js when the child processes return data.

On the other hand, the fork() method can be seen as an extension of the spawn() method. By forking, multiple active worker nodes are established simultaneously, allowing for efficient task handling at any given moment. This approach ensures that there is an ample number of active worker nodes available to handle tasks effectively.

Q.15. What is the use of middleware in Node.js?

Solution: Middleware in Node.js refers to a straightforward function that plays a crucial role in handling incoming requests and outgoing response objects. Its primary functions include:

  • Executing Code: Middleware is responsible for executing code of any kind, such as performing operations, manipulating data, or implementing business logic, as part of the request-response cycle.
  • Updating Request and Response Objects: Middleware has the capability to modify and update the request and response objects, allowing for customizations and transformations as required by the application.
  • Completing Request-Response Iterations: Middleware ensures the completion of the request-response iterations by performing necessary actions and processing before passing control to the next middleware or sending the final response to the client.
  • Calling the Next Middleware: Middleware facilitates the flow of control by calling the next middleware function, enabling a sequential execution of multiple middleware functions in a defined order.

Q.16. What are global objects in Node.js?

Solution: Global objects in Node.js refer to objects that have a scope accessible across all modules of the application. This eliminates the need to include these objects in every module individually. By declaring an object as global, functions, strings, or objects can be accessed throughout the application, promoting code reusability and ease of access.

Moving on to another topic in Node.js coding questions, it is essential to explore the usage of assets in Node.js.

Q.17. What are stubs in Node.js?

Solution: Stubs play a vital role in assessing and analyzing the behavior of individual components during test cases. They are essentially functions that provide detailed insights into the execution of functions, enabling comprehensive testing and evaluation. By utilizing stubs, developers can gain valuable information about how specific functions are executed and their impact on the overall system behavior.

Q.18. How is a test pyramid implemented using the HTML API in Node.js?

Solution: Test pyramids are established by structuring the testing strategy around the HTML API, utilizing the following principles:

  1. Higher Number of Unit Test Cases: Emphasizing a larger quantity of unit test cases helps ensure thorough testing at the component level, validating the functionality of individual units of code.
  2. Smaller Number of Integration Test Methods: Integration tests focus on validating the interaction and integration between various components. While important, they typically involve a smaller number of test methods compared to unit tests.
  3. Fewer Number of HTTP Endpoint Test Cases: HTTP endpoint tests, which validate the behavior and responses of the API endpoints, are typically fewer in number compared to unit and integration tests, as they primarily focus on testing the end-to-end functionality and overall system behavior.

By following this test pyramid structure, the testing strategy ensures comprehensive coverage while maintaining an appropriate balance between different types of tests.

Q.19. Why is a buffer class used in Node.js?

Solution: The Buffer class in Node.js serves as a fundamental tool for data storage. It can be likened to arrays or lists, providing a means to store and manipulate data. Unlike the V8 heap structure, the Buffer class represents a raw memory location.

The global nature of the Buffer class allows its usage across all modules within a Node.js application. This global accessibility enables seamless data sharing and manipulation throughout the different components and modules of the application.

Q.20. Why is ExpressJS used?

Solution: Express.js, a popular framework developed on Node.js, serves as a powerful tool for building web applications. It employs a middleware system that effectively manages the flow of data between servers and server-side applications.

Express.js is renowned for its lightweight nature and flexibility, making it a favored choice for designing mobile applications. It offers a plethora of features and functionalities that cater to the specific requirements of mobile app development, empowering developers to create robust and scalable mobile applications with ease.

Q.21.  What are the types of streams available in Node.js?

Solution: Node.js encompasses support for several types of streams, including:

  1. Duplex Streams: These streams enable both reading from and writing to a resource. They provide bidirectional data flow, allowing for simultaneous reading and writing operations.
  2. Readable Streams: Readable streams facilitate the process of reading data from a source, such as a file or network connection. They allow for sequential data consumption.
  3. Writable Streams: Writable streams enable the writing of data to a destination, such as a file or network connection. They provide an interface for sending data in chunks or continuously.
  4. Transform Streams: Transform streams function as duplex streams that modify or transform the data as it passes through. They can be used for tasks like compression, encryption, or data manipulation during the streaming process.

By supporting these different stream types, Node.js provides flexibility and efficiency in handling data flow and processing operations.

Q.22. What is the use of REPL in Node.js?

Solution: REPL, which stands for Read-Eval-Print-Loop, serves as an interactive and virtual environment within Node.js for testing JavaScript code.

To launch the REPL, users can simply execute the 'node' command in their command-line interface. This opens up a prompt where JavaScript commands can be directly entered and evaluated. The entered code is read, evaluated, and the result is printed back in a continuous loop, allowing for rapid experimentation and testing of JavaScript code snippets in real time.

Q.23. What is meant by tracing in Node.js?

Solution: Tracing is a powerful technique employed to gather comprehensive tracing information generated by V8, the node core, and user-space code. This methodology involves capturing and logging all relevant tracing data into a dedicated log file. This log file serves as a valuable resource for validating and verifying the integrity of the information being transmitted, enabling in-depth analysis and troubleshooting of the system's behavior and performance.

Q.24. What is the difference between readFile and createReadStream in Node.js?

Solution: The readFile function in Node.js allows for asynchronous reading of the entire contents of a specified file. It reads the complete content into memory before making it accessible to users. This method is suitable for smaller files or cases where reading the entire file into memory is not a performance concern.

On the other hand, the createReadStream function is utilized to read a file by breaking it into smaller chunks. By default, each chunk has a size of 64 KB, but this can be adjusted according to specific requirements. This approach is particularly useful for handling large files or scenarios where memory efficiency is a concern, as it allows for streaming and processing data in manageable chunks rather than loading the entire file at once.

Q.25. What is the use of the crypto module in Node.js?

**Solution:**The crypto module in Node.js serves as a valuable tool for implementing cryptographic functionalities. It offers a wide range of wrappers and APIs that enable users to perform various operations related to encryption, decryption, signing, and hashing.

With the crypto module, developers can effortlessly execute operations like ciphering data to ensure confidentiality, deciphering encrypted data, signing data to ensure authenticity and integrity, and performing hash functions for data integrity verification. These capabilities provided by the crypto module empower users to incorporate robust security measures into their Node.js applications.

Q.26. What is a passport in Node.js?

Solution: Passport is a highly popular middleware used in Node.js, specifically designed for authentication purposes. It seamlessly integrates into Express.js-based web applications, making authentication implementation effortless.

Each application requires unique authentication mechanisms, and Passport simplifies this process by providing modular authentication strategies. These strategies can be easily assigned to applications based on specific requirements, eliminating dependencies and ensuring a flexible and customizable authentication setup. With Passport, developers can implement robust authentication systems with ease, enhancing the security and user experience of their Node.js applications.

Q.27. What is the use of EventEmitter in Node.js?

Solution: In Node.js, every object that emits events is essentially an instance of the EventEmitter class. This class provides a mechanism for establishing a connection between objects and named events.

When an EventEmitter object emits an event, synchronous attachments of functions are made. These functions, also known as event handlers or listeners, are executed in response to the emitted event. They allow developers to define custom logic and actions to be performed when specific events occur, enabling event-driven programming in Node.js.

Q.28. What is the difference between setImmediate() and setTimeout()?

Solution: The setImmediate() function in Node.js is designed to execute a given script once the current event loop is complete. It ensures that the provided script is scheduled for immediate execution, allowing other I/O operations to take place without delay.

On the other hand, the setTimeout() function is used to delay the execution of a script by a specified time threshold. It schedules the script to run after the designated delay has passed.

The order of execution between setImmediate() and setTimeout() functions depends on the context in which they are called. If called from the main module, the timing of execution will be influenced by the performance of the underlying process and other factors affecting event loop scheduling.

Q.29. What is the use of module.exports in Node.js?

Solution: The module.exports function in Node.js allows for the exposure of functions or variables from a module, making them accessible in other parts of the application. It provides a way to encapsulate related code into a single module.

A module, in Node.js, acts as a container for organizing and grouping related code into a cohesive unit. It allows developers to logically structure their codebase and separate concerns. By utilizing module.exports, specific functions or variables defined within a module can be made available for use in other parts of the application, enabling modularity and code reuse. This simplifies the organization and management of code by consolidating related functionality into a single file.

Q.30. What are some of the most commonly used libraries in Node.js?

Solution: In the Node.js ecosystem, there are two popular libraries commonly used by developers:

Express.js: Express is a versatile web application framework for Node.js. It offers a comprehensive set of features and functionalities that facilitate the development of web and mobile applications. Express provides a minimalist and flexible approach, allowing developers to build robust and scalable applications with ease. It simplifies routing, middleware integration, and handling of HTTP requests and responses, making it a preferred choice for building web APIs and server-side applications.

Mongoose: Mongoose is a powerful Node.js library that simplifies the process of connecting and interacting with databases, particularly MongoDB. It provides an object modeling interface for MongoDB, allowing developers to define data schemas, perform CRUD operations, and perform advanced querying. Mongoose enhances productivity by providing a higher-level abstraction over MongoDB's native driver, making database operations more intuitive and straightforward.

By leveraging Express.js and Mongoose, developers can create efficient and feature-rich web applications while seamlessly connecting and managing their data storage needs.

Q.31. What are the pros and cons of Node.js?

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Node.js Pros

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Node.js Cons

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Fast processing and an event-based model

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Not suitable for heavy computational tasks

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Uses JavaScript, which is well-known among developers

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Using callback is complex since you end up with several nested callbacks

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Node Package Manager has over 50,000 packages that provide the functionality to an application

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Dealing with relational databases is not a good option for Node.js

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Best suited for streaming huge amounts of data and I/O-intensive operations

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Since Node.js is single-threaded, CPU intensive tasks are not its strong suit

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Q.32. What is the command used to import external libraries?

Solution: The "require" command in Node.js is used to import external libraries or modules into a Node.js application. It allows developers to access and utilize the functionality provided by those libraries within their code. For example, the statement "var http = require('http');" imports the "http" module, which is a built-in module in Node.js, and assigns it to the variable "http". This allows the developer to use the functionality provided by the "http" module in their application.

The "require" command is crucial for leveraging the vast ecosystem of existing Node.js modules and libraries, enabling developers to extend the capabilities of their applications without having to reinvent the wheel.

Q.33. What does event-driven programming mean?

Solution: Event-driven programming is a programming paradigm where the flow of execution is driven by events. Events, such as user interactions or system notifications, trigger specific functions or callbacks that are registered to handle those events. This approach allows for responsive and interactive applications that can react to events as they occur, enabling the decoupling of components and efficient handling of asynchronous tasks.

Q.34.  Differentiate between the process.nextTick() and setImmediate()?

Solution: The distinction between nextTick() and setImmediate() lies in their timing within the event loop.

The nextTick() function in Node.js postpones the execution of a callback until the next pass around the event loop. It ensures that the callback is executed once the current execution of the event loop is complete. This means that any actions scheduled with nextTick() will be prioritized and executed before any I/O operations or timers in the event loop. It is often used to defer the execution of code to a later point in the event loop and is useful for ensuring that certain actions are performed before I/O operations or other asynchronous tasks.

On the other hand, setImmediate() function in Node.js schedules a callback to be executed on the next cycle of the event loop. It allows the event loop to continue processing I/O operations and other callbacks before executing the specified callback. setImmediate() is commonly used when you want to ensure that the callback is executed in a non-blocking manner, giving priority to other I/O operations or timers in the event loop.

In summary, nextTick() executes the callback before I/O operations in the current event loop iteration, while setImmediate() executes the callback in the next event loop iteration, allowing I/O operations to be processed first.

Q.35. How do you create a simple Express.js application?

Solution: To create a simple Express.js application, follow these steps:

  1. Install Express.js by running npm install express.
  2. Import the Express module: const express = require('express').
  3. Create an instance of the Express application: const app = express().
  4. Define routes and their corresponding handlers using app.get(), app.post(), etc.
  5. Start the server by listening on a specific port: app.listen(port).
  6. Access the application in a web browser using the specified port.

Q.36. What are streams in Node.js?

Solution: Streams are utilized to handle continuous data reading or writing in Node.js.

There exist four types of streams:

  • Readable: Designed for reading data.
  • Writable: Intended for writing data.
  • Duplex: Facilitates both reading and writing operations.
  • Transform: Acts as a duplex stream, performing computation on input to produce output.

Q.37. Explain asynchronous and non-blocking APIs in Node.js.

Solution: In Node.js, all library APIs are asynchronous, making them non-blocking in nature.

When a Node.js server calls an API, it does not wait for the data to be returned. Instead, it proceeds to the next API call, and a notification mechanism, facilitated by Node.js events, handles the response from the previous API call.

Q.38. What is a callback function in Node.js?

Solution: A callback is a function that is executed after a specific task has been completed. It allows for non-blocking execution, enabling other code to run concurrently.

Now, let's move on to some advanced-level Node.js interview questions in the final section

Q.39. What is the buffer class in Node.js?

Solution: The Buffer class in Node.js provides a way to store and manipulate raw data, similar to an array of integers. It represents a raw memory allocation outside of the V8 heap. The Buffer class is used when working with binary data because pure JavaScript is not inherently compatible with such data types. By utilizing the Buffer class, Node.js enables efficient handling of binary data within JavaScript applications.

Q.40. What is piping in Node.js?

Solution: Piping is a mechanism in Node.js that allows for connecting the output of one stream to the input of another stream. It is commonly used to transfer data from one stream to another, enabling a seamless flow of data between streams. Piping simplifies the process of retrieving data from one stream and passing it as input to another stream, facilitating efficient data processing in Node.js.

Q.41. What is callback hell?

Solution: Callback hell, also referred to as the pyramid of doom, occurs when there are excessive levels of nested callbacks in code, making it difficult to read, understand, and maintain. This situation arises when asynchronous logic is not properly implemented, leading to a convoluted and tangled callback structure. Callback hell can make code harder to debug and manage, impairing the overall readability and maintainability of the codebase.

Q.42. What is a reactor pattern in Node.js?

Solution: The reactor pattern is a design concept that facilitates non-blocking I/O operations. It involves associating a handler with each I/O operation. When an I/O request is initiated, it is submitted to a demultiplexer. The demultiplexer is responsible for monitoring multiple I/O sources and determining which ones are ready for processing. Upon receiving the notification from the demultiplexer, the associated handler is invoked to handle the I/O operation in a non-blocking manner. The reactor pattern enables efficient handling of I/O operations by allowing the system to continue processing other tasks while waiting for I/O events to occur.

Q.43. What are the different types of HTTP requests?

Solution: HTTP defines various request methods that serve different purposes. Some commonly used request methods include:

  • GET: Used to retrieve data from a server. It is a safe and idempotent method, meaning it should not have any side effects on the server.
  • POST: Used to submit data to the server to create a new resource or trigger a specific action. It can have side effects on the server.
  • HEAD: Similar to the GET method, it only requests the headers of the response without the actual response body. It is often used to retrieve metadata about a resource without transferring its entire content.
  • DELETE: Used to request the removal of a specified resource on the server.

These request methods provide a standardized way for clients to interact with servers and perform various operations based on the specific requirements of an application.

Q.44. What is a first-class function in Javascript?

Solution: First-class functions in JavaScript and Node.js refer to the ability to treat functions as values. This allows functions to be assigned to variables, passed as arguments to other functions, and returned as values from functions. In Node.js, first-class functions are extensively used in asynchronous programming to write non-blocking code and handle high-concurrency I/O operations effectively. They enable the use of callback functions and higher-order functions, facilitating the creation of flexible and reusable code patterns.

Q.45. What is the difference between JavaScript and Node.js?

Solution: Node.js is a runtime environment that allows the execution of JavaScript code outside of a web browser. It provides additional capabilities and APIs, such as file system access and networking, that are not available in a browser environment. JavaScript, on the other hand, is the programming language itself and can be executed both in web browsers and in the Node.js runtime environment. Node.js extends the functionality of JavaScript and enables its usage for server-side and command-line applications.

Q.46. What are the asynchronous tasks that should occur in an event loop?

Solution: Asynchronous tasks that should occur in an event loop in Node.js include I/O operations, timers, and callback functions. By performing these tasks asynchronously, Node.js can handle a large number of concurrent requests without blocking the event loop.

Q.47. What is the order of execution in control flow statements?

Solution: In Node.js, control flow statements are executed in a specific order. The order of execution is determined by the event loop. The event loop is a mechanism in Node.js that allows for the execution of non-blocking I/O operations.

Q.48. What are the input arguments for an asynchronous queue?

Solution: An asynchronous queue in Node.js is a data structure that allows for the execution of functions in a specific order. Functions are added to the queue and are executed in the order that they were added. An asynchronous queue is useful when you want to execute a series of functions in a specific order.

Q.49. What is the difference between Node.js and Ajax?

Solution: Ajax and Node.js are two different technologies that are used for different purposes. Ajax is a client-side technology that allows for asynchronous communication between the client and the server. It is typically used to update parts of a web page without requiring a full page reload.

Node.js, on the other hand, is a server-side technology that is used for building fast, scalable, and efficient server-side applications. It is typically used for real-time applications, such as chat applications, online games, and streaming services.

Q.50. What is the advantage of using Node.js?

Solution: Node.js is fast and scalable. Node.js is easy to learn and use. Node.js is well-suited for real-time applications, such as chat applications, online games, and streaming services. This is because Node.js can handle a large number of connections and can perform non-blocking I/O operations, which makes it ideal for real-time communication.

Q.51. What is "non-blocking" in node.js?

Solution: In Node.js, non-blocking refers to the ability of the runtime environment to execute multiple tasks simultaneously without waiting for the completion of one task before starting the next. This is achieved through the use of asynchronous I/O operations, which allow Node.js to handle multiple requests concurrently.

Q.52. How does Node.js overcome the problem of blocking I/O operations?

Solution: Node.js uses an event-driven, non-blocking I/O model that allows it to handle I/O operations more efficiently. By using callbacks, Node.js can continue processing other tasks while waiting for I/O operations to complete. This means that Node.js can handle multiple requests simultaneously without causing any delays. Additionally, Node.js uses a single-threaded event loop architecture, which allows it to handle a high volume of requests without any issues.

Q.53. How can we use async await in node.js?

Solution: To use async/await in Node.js, you'll need to use functions that return promises. You can then use the async keyword to mark a function as asynchronous and the await keyword to wait for a promise to resolve before continuing with the rest of the code.

Q.54. Why should you separate the Express app and server?

Solution: Firstly, separating your app and server can make it easier to test your code. By separating the two, you can test your app logic independently of the server, which can make it easier to identify and fix bugs.

Secondly, separating your app and server can make it easier to scale your application. By separating the two, you can run multiple instances of your app on different servers, which can help to distribute the load and improve performance.

Finally, separating your app and server can make it easier to switch to a different server if necessary. By keeping your app logic separate from your server logic, you can switch to a different server without having to make any major changes to your code.

Q.55. Explain the concept of stub in Node.js.

Solution: In Node.js, a stub is a function that serves as a placeholder for a more complex function. Stubs are typically used in unit testing to replace a real function with a simplified version that returns a predetermined value. By using a stub, you can ensure that your unit tests are predictable and consistent.

Q.56. What are the security implementations that are present in Node.js?

Solution: One of the most important security features in Node.js is the ability to run code in a restricted environment. This is achieved through the use of a sandboxed environment, which can help to prevent malicious code from accessing sensitive data or causing any damage to the system.

Another important security feature in Node.js is the ability to use TLS/SSL to encrypt data in transit. This can help to prevent eavesdropping and ensure that sensitive data is protected.

Q.57. What is the use of the connect module in Node.js?

Solution: The Connect module can be used to handle different types of middleware, such as error-handling middleware, cookie-parsing middleware, and session middleware. Error-handling middleware is used to handle errors that occur during the request/response cycle. Cookie parsing middleware is used to parse cookies from the request header. Session middleware is used to manage user sessions.

Q.58. What's the difference between 'front-end' and 'back-end' development?

Solution: Front-end developers focus on the client side of the application, while back-end developers focus on the server side of the application. Both roles are important for building a successful web application and require different skill sets and expertise.

Q.59. What are LTS releases of Node.js?

Solution: LTS stands for Long-term support. LTS releases of Node.js are versions that are supported for an extended period, usually for 30 months from the time of release. These releases are typically more stable and reliable than non-LTS releases and are recommended for production use.

Q.60.  How does Node.js handle the child threads?

Solution: Node.js utilizes child processes to achieve parallelism and avoid blocking the main event loop. It creates separate instances of the Node.js runtime environment to execute code in parallel with the main process. This enables Node.js to scale better and make better use of available resources.

Q.61. How to Enhance Node.js Performance through Clustering?

Solution: Clustering can be used to improve the performance of HTTP servers, database connections, and other I/O operations. However, it is important to note that clustering does not guarantee a linear increase in performance.

Q.62. What is a thread pool, and which library handles it in Node.js?

Solution: A thread pool is a collection of threads that are used to execute tasks in parallel. In Node.js, the thread pool is handled by the libuv library, which is a multi-platform support library that provides asynchronous I/O operations.

Q.63. How are worker threads different from clusters?

Solution: Worker threads and clusters are two different approaches to leveraging the power of multiple CPUs in Node.js. While clusters create multiple instances of a Node.js process, each running on a separate CPU core, worker threads provide a way to create multiple threads within a single process.

Q.64. How to measure the duration of async operations?

Solution: The console.time and console.timeEnd methods allow you to measure the duration of a block of code. The console.time method is used to start the timer and the console.timeEnd method is used to stop the timer and log the duration to the console.

The performance.now method provides a more precise way to measure the duration of async operations. It returns the current timestamp in milliseconds, which can be used to calculate the duration of a task.

Q.63. How to measure the performance of async operations?

Solution: There are several tools and techniques you can use to measure performance, including using the built-in --prof flag, using the perf tool, and using third-party libraries like benchmark.js.

Q.64. What is the difference between readFile and create Read Stream in Node.js?

Solution: Create Read Stream is a better option for reading large files, while the read file is a better option for small files. It is important to choose the right method based on the size of the file and the requirements of the application.

Q.65. What is meant by tracing in Node.js?

Solution: Tracing is a technique used in Node.js to profile the performance of an application. It involves recording the function calls and events that occur during the execution of the application and analyzing the data to identify performance bottlenecks.

Q.66. What is the use of the crypto module in Node.js?

Solution: The crypto module is widely used in Node.js applications to generate secure random numbers, create digital signatures, and verify signatures. It also provides support for various encryption algorithms such as AES, DES, and RSA.

Q.67. What is a passport in Node.js?

Solution: Passport is a popular authentication middleware for Node.js. It provides a simple and modular way to implement authentication in Node.js applications. Passport supports many authentication mechanisms, including username/password, social logins like Facebook and Google, and JSON Web Tokens (JWTs).

Q.68. How to get information about a file in Node.js?

Solution: In Node.js, the fs module provides methods for working with the file system. To get information about a file, you can use the fs. stat() method. The fs. stat() method returns an object that contains information about the file, such as the file size, creation date, and modified date.

Q.69. What is the difference between setImmediate() and setTimeout()?

Solution: The setTimeout() method schedules code execution after a specified delay, measured in milliseconds. On the other hand, the setImmediate() method schedules code execution to occur immediately after the current event loop iteration completes. This means that setImmediate() has a higher priority than setTimeout().

Q.70. Explain the concept of Punycode in Node.js.

Solution: Punycode is a character encoding scheme used in the domain name system (DNS) to represent Unicode characters with ASCII characters. It is used to encode domain names that contain non-ASCII characters, such as Chinese or Arabic characters.

Q.71. Is cryptography supported in Node.js?

Solution: Node.js has a built-in crypto module that provides support for cryptographic functions like hashing, encryption, and decryption. It's easy to use and offers a range of algorithms, including AES for symmetric encryption and SHA-256 and SHA-512 for hashing. With this module, developers can generate random bytes, create HMACs, public and private key pairs, sign and verify messages, and more. By using the crypto module, developers can easily secure their applications and data.

Q.72. Does Node.js provide any Debugger?

Solution: Node.js offers a built-in crypto module that enables developers to perform various cryptographic functions without the need for external libraries. The module is designed to be user-friendly and provides support for a range of algorithms, including symmetric encryption and hashing. With the crypto module, developers can easily generate secure random data, create HMACs, generate public and private key pairs, sign and verify messages, and more. Using this module can help ensure the security of Node.js applications and data.

Q.73. What is the significance of the "__dirname" variable in Node.js?

Solution: In Node.js, "__dirname" is a global variable that represents the absolute path of the directory that contains the currently executing file. It allows you to create paths that are relative to the current file's location, making it useful when requiring modules or referencing other files or directories located relative to the current file.

Q.74. How do you manage dependencies in a Node.js project?

Solution: To manage dependencies in a Node.js project, use a package manager such as npm or Yarn. The general steps are to create a package.json file, install dependencies using "npm install," save dependencies using "npm install --save", manage dependencies with "npm ls" and "npm update," and use dependencies with the "require" function. Managing dependencies this way enables easy installation, updating, and removal of packages, tracks, and version dependencies and facilitates sharing and collaboration.

Q.75. Can you explain what the "require" function does in Node.js?

Solution: In Node.js, the "require" function is used to load and use modules that are defined in separate files. It searches for modules in core modules, local modules, and third-party modules. Once a module is found, its contents are loaded into a new object and returned. The "require" function allows you to modularize your code and build complex, modular applications.

Q.76. How do you handle concurrency in Node.js?

Solution: Node.js handles concurrency through an event-driven, non-blocking I/O model. Asynchronous functions, worker threads, cluster modules, and load balancers are some techniques used to handle concurrency in Node.js. These techniques allow developers to build high-performance, scalable applications that can handle a large number of concurrent requests.

Q.77. What are some common security vulnerabilities in Node.js applications, and how do you prevent them?

Solution: To prevent security vulnerabilities in Node.js applications, it is important to implement input validation and sanitation, use security-focused middleware, follow secure coding practices, keep dependencies up-to-date, use rate limiting and other defensive mechanisms, use HTTPS, use a security-focused hosting platform. By following these best practices, developers can help ensure that their Node.js applications are secure and protected from potential security threats.

Q.78. What is the purpose of the "path" module in Node.js?

Solution: The "path" module in Node.js provides utilities for working with file and directory paths. It helps developers write cross-platform code by providing a consistent way to work with file paths. Functions like "join," "resolve," and "dirname" can manipulate file paths regardless of the operating system. For example, the "basename" function gets the file name, and the "dirname" function gets the directory path.

Q.79. What are some best practices for writing efficient and scalable Node.js code?

Solution: Some best practices for writing efficient and scalable Node.js code include:

  • Avoid blocking I/O operations: Use non-blocking I/O operations and callbacks to ensure that your code can handle multiple requests simultaneously.
  • Use a process manager: Use a process manager like PM2 to manage your Node.js processes to ensure that they run smoothly and can be easily monitored.
  • Optimize code for performance: Use profiling tools to identify performance bottlenecks in your code, and optimize accordingly.
  • Use caching: Implement caching mechanisms to reduce the number of requests to your server and improve performance.
  • Use streams: Use streams to handle large amounts of data efficiently without loading it all into memory at once.

Q.80. How do you handle errors in Node.js applications?

Solution: In Node.js applications, errors can be handled using try-catch blocks, error-first callbacks, and middleware functions. Here are some approaches for handling errors in Node.js:

  1. Try-catch blocks: Use try-catch blocks to catch synchronous errors in your code.

Example:

try {
  // some code that may throw an error
} catch (err) {
  console.error(err);
}
  1. Error-first callbacks: Use error-first callbacks to handle asynchronous errors in your code. An error-first callback is a callback function that takes an error object as its first argument.

Example:

fs.readFile('/path/to/file', (err, data) => {
  if (err) {
    console.error(err);
    return;
  }
  console.log(data);
});
  1. Middleware functions: Use middleware functions to handle errors that occur in your application. Middleware functions are functions that can be used to handle requests and responses in your application.

Example:

app.use((err, req, res, next) => {
  console.error(err);
  res.status(500).send('Internal Server Error');
});

By handling errors in your Node.js application, you can improve its stability and reliability and ensure that your users have a better experience.

Q.81. What is the difference between callback-based and Promise-based asynchronous programming in Node.js?

Solution: Callback-based asynchronous programming is an older approach that passes a function as an argument to an asynchronous function, while Promise-based programming is a newer approach that uses Promise objects to represent the eventual completion of an asynchronous operation. Promises simplify error handling and provide a cleaner syntax, while callbacks can be harder to read and maintain. Node.js supports both approaches.

Q.82. What is the purpose of the "fs" module in Node.js, and how is it used for file I/O operations?

Solution: The "fs" module in Node.js provides functionality for file I/O operations, such as reading, writing, updating, and deleting files. It allows Node.js applications to interact with the file system on the local machine or server. The module provides both synchronous and asynchronous methods for file I/O operations, allowing developers to choose the most appropriate approach for their use case. For example, "fs.readFile" is an asynchronous method that reads the contents of a file, while "fs.readFileSync" is a synchronous method that reads the contents of a file. Developers can also use the "fs" module to create, move, rename, and delete files and directories.

Q.83. How do you optimize the performance of a Node.js application?

Solution: There are several ways to optimize the performance of a Node.js application, including:

  1. Minimizing blocking operations: Use asynchronous, non-blocking operations wherever possible to avoid blocking the event loop.
  2. Using a load balancer: Distribute incoming requests across multiple servers to prevent overload on a single server.
  3. Implementing caching: Cache frequently accessed data in memory or use a caching service to reduce the number of requests to the server.
  4. Implementing server-side rendering: Pre-rendering server-side components of your application can improve the load time for users.
  5. Monitoring and profiling: Monitor your application's performance using tools like Node.js Profiler or New Relic to identify performance bottlenecks and optimize your code.

By implementing these strategies, you can significantly improve the performance of your Node.js application.

Q.84. How do you deploy a Node.js application to a production server?

Solution: Deploying a Node.js application to a production server typically involves the following steps:

  1. Choose a hosting provider: There are many hosting providers that support Node.js applications, such as AWS, Google Cloud, and Heroku. Choose a provider that suits your needs and budget.
  2. Set up the server: Once you have chosen a provider, you need to set up a server to host your application. This involves creating an instance, configuring security settings, and installing any required dependencies.
  3. Configure environment variables: You should configure environment variables on your server to store sensitive information, such as API keys and database credentials.
  4. Deploy the application: There are different ways to deploy a Node.js application, such as using Git or an FTP client. You should choose a method that works best for your project.
  5. Start the application: Once the application is deployed, you need to start it on the server. This typically involves running a command like "npm start" or "node app.js".
  6. Monitor the application: You should monitor your application for errors and performance issues using tools like PM2 or New Relic.

By following these steps, you can deploy a Node.js application to a production server and ensure that it is secure, stable, and performant.

Q.85. What is the difference between the "require" and "import" statements in Node.js?

Solution: The require statement is the traditional way of importing modules in Node.js, while the import statement is a newer way introduced in ECMAScript 6 (ES6) that provides more advanced features such as named imports and default exports. The import statement is also syntactically different from the require statement, as it uses the ES6 module syntax rather than the CommonJS syntax used by require. However, import is not yet natively supported in Node.js and requires the use of a transpiler such as Babel. Therefore, in most Node.js applications, the require statement is still the preferred way of importing modules.

Q.86. What is serverless computing, and how can you use it with Node.js?

Solution: Serverless computing is a cloud computing model where the cloud provider manages the infrastructure and automatically allocates resources as needed. With Node.js, you can use serverless computing platforms such as AWS Lambda or Google Cloud Functions to write and deploy functions that are triggered by events or HTTP requests without having to worry about managing servers or scaling infrastructure.

Q.87. What is the purpose of the "os" module in Node.js, and how is it used for system-level operations?

Solution: The "os" module in Node.js provides a set of utilities for operating system-related tasks. It can be used to get information about the system's operating system, CPU, memory, network interfaces, and more. The module also provides functions for performing platform-specific operations, such as creating child processes and handling signals. This module is useful for building cross-platform applications that require system-level access.

Q.88.  How can you maintain code organization and modularity over time?

Solution: To maintain code organization and modularity over time in a Node.js project, you can follow these best practices:

  1. Use a modular architecture: Break your code into modules that perform specific functions and can be easily tested and reused. This can be done using features like modules, classes, and functions.
  2. Use version control: Use a version control system like Git to track changes to your code over time, and ensure that your project remains organized and easy to maintain.
  3. Use a consistent coding style: Adopt a consistent coding style across your project to make it easier to read, understand, and maintain. Use tools like ESLint to enforce coding standards and catch potential errors.
  4. Use automated testing: Write automated tests to ensure that changes to your code do not break existing functionality. This helps maintain code organization and modularity over time.
  5. Use documentation: Document your code using tools like JSDoc to help other developers understand how your code works and how to use it. This makes it easier to maintain code organization and modularity over time.

By following these best practices, you can maintain code organization and modularity over time, making it easier to develop, test, and maintain your Node.js project as it evolves.

Q.89. How do you handle database interactions in a Node.js application, and what libraries or frameworks are commonly used?

Solution: In Node.js, database interactions can be handled using libraries or frameworks like Sequelize, Mongoose, or knex.js. These libraries provide a higher-level API for interacting with databases and can help manage connections, handle queries, and model data. Additionally, it is common to use the asynchronous nature of Node.js to handle database operations in a non-blocking way to improve application performance.

Q.90. How do you use environment variables in a Node.js application, and why are they important?

Solution: Environment variables are a key aspect of configuring and deploying Node.js applications. They allow you to specify configuration values, API keys, and other sensitive information outside of your codebase, making it easier to manage and secure your application.

In Node.js, you can access environment variables using the process.env object. You can set environment variables locally using a .env file or through your system's command line interface. When deploying to production, you can set environment variables through your hosting provider or cloud service.

By using environment variables, you can easily manage configuration values for different environments (development, staging, production), keep sensitive information separate from your codebase, and make it easier to deploy and scale your application.

Q.91. What is the purpose of the "net" module in Node.js, and how is it used for creating TCP/IP servers and clients?

Solution: The "net" module in Node.js provides a way to create TCP/IP servers and clients for network communication. It allows developers to create TCP servers that listen for incoming connections, as well as TCP clients that can initiate connections to remote servers. The module provides methods for creating both server and client instances, as well as for sending and receiving data over the network. Additionally, the "net" module also provides options for configuring the behavior and settings of TCP connections.

Q.92. How do you implement caching in a Node.js application, and what caching strategies are commonly used?

Solution: To implement caching in a Node.js application, you can use in-memory caching, distributed caching, or persistent caching. In-memory caching is useful for storing small amounts of data, while distributed caching is better suited for larger data sets and high-traffic applications. Persistent caching involves storing data on disk, which can help reduce load times and improve performance. Commonly used caching libraries in Node.js include Redis, Memcached, and Node-cache. To implement caching, you can use caching middleware or cache API calls manually in your code. It is important to consider cache expiration policies, cache invalidation strategies, and potential memory issues when implementing caching in your application.

Q.93. What is the difference between a monolithic and microservices architecture, and how does Node.js fit into each one?

Solution: A monolithic architecture is a traditional approach where an application is built as a single, large codebase with all components tightly coupled together. In contrast, a microservices architecture is an approach where an application is composed of small, independently deployable services that communicate with each other via APIs.

Node.js can be used in both monolithic and microservices architectures. In a monolithic architecture, Node.js can be used to build the entire application as a single, scalable unit. In a microservices architecture, Node.js can be used to build individual services that are lightweight and can be easily deployed and scaled independently. Node.js is particularly well-suited for building microservices due to its non-blocking I/O and event-driven architecture.

Q.94. What is the purpose of the "events" module in Node.js, and how is it used for event-driven programming?

Solution: The "events" module in Node.js is a core module that provides a way to handle and respond to events. It allows developers to create and emit custom events and build event-driven applications. The module provides an EventEmitter class that serves as a central hub for registering and triggering event listeners. Developers can use this module to create custom event emitters and listeners, which can be useful in scenarios such as building a real-time chat application or handling file system events.

Q.95. What is the purpose of the "child_process" module in Node.js, and how is it used for running external processes?

Solution: The "child_process" module in Node.js is used for running external processes, such as system commands or other executables. It provides a way to spawn child processes and communicate with them using streams or callbacks. This module can be used to run CPU-intensive tasks in separate processes to avoid blocking the main Node.js event loop or to interact with other programs and services on the system. The "child_process" module also supports spawning child processes with different options, such as running them in detached mode or with custom environment variables.

Q.96. What is the purpose of the "cluster" module in Node.js, and how is it used for load balancing?

Solution: The "cluster" module in Node.js is used to enable the creation of child processes that can share server ports, allowing for load balancing across multiple CPU cores. Each child process runs in a separate thread and can handle incoming requests. The module provides several strategies for distributing the workload, such as round-robin, and can also restart failed processes automatically. This helps to improve the performance and reliability of Node.js applications by utilizing the full potential of the underlying hardware.

Q.97. How can you debug and profile Node.js applications for performance issues?

Solution: To debug and profile Node.js applications for performance issues, you can use the built-in debugging tools in Node.js, such as the Node.js Debugger and the Chrome DevTools. You can also use third-party tools like Visual Studio Code, which has built-in debugging support for Node.js applications. To profile the performance of a Node.js application, you can use the built-in Node.js Profiler or third-party profiling tools like Node.js-Prof. Additionally, you can use load testing tools like Artillery and Apache JMeter to simulate high traffic and measure the performance of your Node.js application under stress.

Q.98. How can you handle file uploads in a Node.js web application?

Solution: To handle file uploads in a Node.js web application, you can use the "multer" middleware. Here are the general steps:

  • Install "multer" using npm
  • Require "multer" in your application
  • Configure "multer" with the desired settings, such as the destination directory and filename
  • Add the "multer" middleware to your file upload route
  • Access the uploaded file in your route handler using the "req.file" object

With "multer," you can easily handle file uploads in your Node.js web application and customize the upload settings as needed.

Q.99. What are some popular Node.js frameworks for building web applications, and what are their key features?

Solution: Node.js has several popular frameworks for building web applications, including Express, Koa, Hapi, NestJS, and Sails.js.

Express is the most widely used Node.js framework and is known for its simplicity, flexibility, and robust routing capabilities. Koa is a lightweight framework with a focus on modularity and easy error handling. Hapi is a configuration-centric framework that emphasizes security and extensibility. NestJS is a TypeScript-based framework that uses decorators to enable modular and scalable code. Sails.js is an MVC framework that uses Waterline ORM to simplify database management.

Each framework has its own unique features and strengths, and the choice of which one to use depends on the specific needs and requirements of the project.

Q.100. How can you secure a Node.js web application from common security vulnerabilities, such as XSS and CSRF attacks?

Solution: To secure a Node.js web application from common security vulnerabilities, such as XSS and CSRF attacks, developers should follow best practices, such as input validation, output encoding, and session management. They can also use middleware modules, such as Helmet, to add extra security headers to HTTP responses. Additionally, implementing measures such as HTTPS, Content Security Policy (CSP), and rate limiting can help to further enhance the security of the application. It's also essential to keep dependencies up-to-date and regularly perform security audits to identify and address any potential vulnerabilities.

Conclusion

In conclusion, our extensive guide on 'Node.js interview questions' serves as a valuable resource for developers of all experience levels. By providing a comprehensive list of 100 essential questions spanning from the basics to advanced concepts, this guide is designed to help you navigate the Node.js interview process with confidence and poise.

Remember, practice makes perfect. As you work through these questions and deepen your understanding of Node.js, your confidence will grow, allowing you to tackle even the most challenging interviews. Keep honing your skills, and don't be afraid to revisit this guide whenever you need a refresher. For more fundamental concepts check out our free Node Js Tutorial.

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