Do you think IIT Guwahati certified course can help you in your career?
No
Introduction
Welcome readers! We hope that you are doing well.
So, you are also preparing for the Node.js Interview, and your interview is approaching. Are you getting nightmares about Node.js interview questions? Don’t worry, you are in the right place. We have come up with the most commonly asked Node.js interview questions in this article. So leave all your worries and follow the article till the end to ace all the Node.js Interview questions with grace.
If you want to learn the basics of the node, then you can refer to the link Basics of Node.
In this article, we will cover the most commonly asked Node.js interview questions to help you prepare for your next job interview. Node.js is a powerful, open-source, server-side runtime environment used to build fast and scalable network applications. If you want to boost your chances of landing a role as a Node.js developer, these questions and answers will give you a strong foundation to ace your interview.
This blog will make you confident before appearing for any Node.js Interview, and also it will help you extend your knowledge about the Node.js Interview questions and fundamental concepts of Node.js. We hope that you will be able to grasp all Node.Js interview questions with ease.
So, without any further ado, let’s dive deep into a few common Node.Js interview questions.
Beginner Node.js Interview Questions
The most commonly asked interview questions are as follows,
1. What is Node.js?
Node.js is an Open source, cross-platform web application JavaScript runtime environment built on Google Chrome’s V8 JavaScript engine. Node.js comes with a runtime environment on which a JavaScript-based script can be interpreted and executed. This runtime allows running a JavaScript code outside of a browser. If you want to learn the basics of the node, then you can refer to the link Basics of Node.
2. Why use Node.js?
Some of the advantages of Node.js include: a) Node.js library is very fast as it is built on Google Chrome’s V8 JavaScript engine.
b) All APIs in the Node.js library are asynchronous, which means a Node.js based server never waits for an API to return data rather, it moves to the next API after calling it. c) Node.js uses a single-threaded model with the event looping. The event mechanism helps the server respond in a non-blocking way which makes the server highly scalable.
d) Node.js is portable. It is available in different operating systems like Windows, Linux, macOS, Solaris, freeBSD etc.
3. Explain the flow diagram of Node.js?
A web server using Node.js has a workflow that typically looks like the below diagram.
The above diagram states that
a) The clients send requests to the webserver to interact with the web application. The requests can be blocking or non-blocking.
b) After receiving all the requests, js add those requests to the event queue.
c) After that, the requests are passed through the event loop. It also checks if the requests require any external resources.
d) The event loop processes the non-blocking requests and returns the responses.
e) For a blocking request, a single thread from the thread pool is assigned. This thread is responsible for completing a particular blocking request by accessing external resources like computation, database, file system etc.
f) After completing the task, the response is sent back to the event loop that sends the response back to the client.
4. Explain why Node.js is single-threaded?
Node.js was created for experimenting the async processing. The theory behind doing so was that the async processing on a single thread under typical web loads could provide more performance and scalability than the typical thread-based implementation.
5. How many types of API functions are available in Node.js?
In Node.js, there are two types of API functions:
a) Asynchronous and Non-blocking functions. b) Synchronous, Blocking functions.
6. Explain what the callback is in Node.js?
A callback in Node.js is a function that is called after a given task. Thus it helps in preventing any blocking.
7. Explain what the Event Loop is in Node.js?
Despite being a single-threaded application, Node.js supports concurrency through the concept of events and callbacks. As every API of Node.js is asynchronous, it uses the async function calls to maintain the concurrency. The event loop allows Node.js to perform non-blocking operations despite being single-threaded. It is an endless loop that waits for tasks from the event queue, executes them and then sleeps until it receives the next task.
8. What is REPL in the context of Node?
The REPL stands for Read Eval Print Loop. REPL represents a computer console where a command is given, and the system responds with an output.
Node.js also comes with a REPL environment which is described below, a)Read: Read and parse the input. b) Eval: Evaluates the data structure. c) Print: Prints the result. d)Loop: Loops the above command until the user terminates.
9. What is the use of the “_” variable in REPL?
The “_” variable is used to get the last result.
10. Explain what the first-class function in JavaScript is?
The first-class functions in JavaScript are treated like any other variable. These first-class functions can be passed as a parameter to any other function or return any other function.
11. What is NPM?
NPM stands for Node Package Manager. It is responsible for managing packages and modules for Node.js.
12. What is the main functionality of the NPM?
The NPM mainly provides two main functionalities: a) It provides online repositories for Node.js packages or modules which are searchable on search.nodejs.org b) It provides a common line utility to install packages, and also it manages Node.js versions and dependency.
Intermediate Node.js Interview Questions
13. What do you mean by the modules in Node.js?
Modules in Node.js are the block of encapsulated code that perform some functionality. It can be a single file or a set of files. It can be used in Node.js applications to include a set of functions. Modules are essential from a programmer's perspective as you can reuse them in a different code section.
Modules can be of different types like the core modules, local modules and third-party models. Core modules are the built-in modules that come from the Node.js installation. Local modules are the user-defined modules created locally in your Node.js application. Third-party modules are available online and can be installed in the Node.js application using npm.
To include a module in Node.js, you need to use the “require()” function with the module name. Like, If you want to include the “http” core module in your Node.js module,
var module = require('http');
14. Explain different core modules in Node.js?
The different core modules of Node.js are discussed below:
Core Modules
Description
http
Creates an HTTP server in Node.js.
assert
Includes a set of assertion functions that are useful for testing.
fs
Used to handle file systems to deal with I/O operations.
path
Includes methods to deal with file paths.
url
Includes methods for URL parsing.
process
Provides information and control about the current Node.js process.
os
Provides information about the operating system.
querystring
Includes methods to work with query strings.
15. What is the purpose of using the module. Exports in Node.js?
Modules in Node.js is the block of encapsulated code that can be parsed by moving all relevant functions into a single file. The “module.exports” exports a module that lets the module be imported into another file with a needed keyword.
16. What are some of the most commonly used libraries in Node.js?
There are mainly two commonly used libraries in Node.js:
a)Express JS: Express is a flexible Node.js application framework that provides many features to develop web and mobile applications. b) Mongoose: Mongoose is a Node.js application framework used to connect an application to a database.
17. What is the “package.json” file?
A package.json file defines the properties of a package, and it is present in the root directory of your Node.js application.
When you create your Node application by running the npm init command, it automatically creates a package.json file in the root directory of your NOde application.
The structure of the package.json file is something like the below,
18. How do you install, update and delete a dependency?
Installing a dependency: npm install dependency_name Updating a dependency: npm update Deleting a dependency: npm uninstall dependency_name
19. How do you create a server in Node.js?
There are a few steps to be followed to create a server in Node.js: a) First, import the HTTP module. b) Then, use the createServer() function that takes a callback function with request and response parameters. c) Listen for any incoming requests.
var http = require('http'); var server = http.createServer(function (req, res) { }); server.listen(5000);
20. What are the different types of HTTP requests in Node.js?
HTTP provides different types of methods that are used to perform different actions. The request methods include
HTTP Requests
Description
GET
Used to retrieve the data.
POST
Generally used to make some changes in a state on the server.
HEAD
It is similar to the GET request, but it asks for the response without the response body.
DELETE
Used to delete a predetermined resource.
21. What is the buffer class in Node.js?
The buffer class in Node.js is defined to handle and store the raw binary data that is similar to an array of integers. Each buffer corresponds to a raw memory allocation outside of V8. Unlike arrays, they are not resizable.
22. What is piping in Node.js?
Piping is a mechanism used to connect the output of one stream to another stream. The main purpose of the piping is to retrieve data from one stream and pass it to another stream.
23. What is callback hell?
Callback hell in Node.js is the situation in which we have complex nested, unreadable, unmanageable callbacks, making the code harder and more complex to read, test, and debug.
24. What do you understand by the term fork in Node.js?
Typically, a fork is used to spawn child processes. In Node.js, fork() is used to create new instances of the V8 engine. Here multiple workers run on a single node code base for multiple tasks.
25. What are the pros and cons of Node.js?
The pros and cons of Node.js are discussed below:
Pros
Cons
It uses JavaScript which is easy to learn.
Use of the callback is not suited if you end up having a complex and huge amount of callbacks.
It uses the Asynchronous event-driven IO which helps in concurrent request handling.
Dealing with relational databases is not a good option in Node.js.
The Node Package Manager (NPM) provides a huge number of packages to provide the functionality of an application.
Not suited for CPU-intensive tasks. Only suited for the I/O stuff only.
Advanced Node.js Interview Questions
26. What is the difference between process.nextTick() and setImmediate()?
The primary difference between process.nextTick() and setImmediate() lies in their execution timing within the event loop. process.nextTick() schedules a callback to be executed in the same phase of the event loop, after the current operation completes but before any I/O operations. This makes it useful when you want to prioritize the execution of certain code. On the other hand, setImmediate() schedules the callback for the next iteration or “tick” of the event loop, specifically during the “check” phase. setImmediate() is ideal for running I/O-bound code without blocking subsequent operations.
27. What is cluster mode in Node.js?
Cluster mode allows Node.js to take full advantage of multi-core systems by launching multiple child processes (workers) that can handle incoming requests concurrently. Each worker shares the same server port, and the operating system distributes the load between the processes. This significantly improves performance for high-traffic applications. The cluster module simplifies this by allowing developers to fork the main process as needed. Additionally, workers can communicate with each other through IPC (Inter-Process Communication). This mode is essential for improving scalability in Node.js applications running in production environments.
28. How do you handle uncaught exceptions in Node.js?
In Node.js, uncaught exceptions can be handled using process.on('uncaughtException'). This event listener catches exceptions that haven’t been handled by try-catch blocks. It is crucial for preventing the entire process from crashing. However, relying solely on this method is discouraged in production because it doesn’t cleanly exit the application or restore its consistent state. Best practices include using Promises with .catch() methods or structured error-handling middleware in frameworks like Express. Tools like domains (deprecated) or custom logging services can also aid in managing unhandled exceptions for better control over application failures.
29. Explain how streams work in Node.js.
Streams in Node.js are a core feature designed to handle large data sets efficiently by processing data in small, manageable chunks instead of reading or writing the entire dataset at once. This makes streams particularly well-suited for operations involving large files, network requests, or real-time data transmission, where buffering everything could consume significant memory and slow down performance.
Streams are instances of EventEmitter, which means they operate asynchronously and emit events like data, end, and error to handle the flow of data. There are four main types of streams in Node.js:
Readable Streams: Used for reading data. Example: fs.createReadStream() for reading files.
Writable Streams: Used for writing data. Example: fs.createWriteStream() for writing to files.
Duplex Streams: Both readable and writable. Example: network sockets.
Transform Streams: Modify or transform data while reading and writing. Example: compressing files.
The pipe() method is one of the most powerful features of Node.js streams, allowing automatic handling of data flow between a readable stream and a writable stream. This ensures smooth, back-pressure aware, and memory-efficient data transfer, as data is passed in chunks instead of being fully loaded into memory.
By utilizing streams, developers can significantly improve the efficiency and performance of applications, particularly when working with large data sets or I/O-heavy tasks.
30. What is event-driven programming in Node.js?
Event-driven programming is a core concept in Node.js, where the flow of the program is determined by events such as user actions, messages from other programs, or I/O operations. In this model, Node.js runs on a single-threaded event loop, where events are triggered, and callback functions are executed asynchronously. The event loop allows Node.js to handle multiple I/O operations without blocking the execution of code, making it ideal for high-concurrency applications such as servers. This non-blocking nature ensures that tasks like network requests are handled efficiently without slowing down other operations.
31. How does the Node.js event loop work?
The Node.js event loop is the mechanism responsible for executing JavaScript code, handling I/O operations, and processing callbacks in an asynchronous manner. The event loop operates in phases, such as timers, pending callbacks, idle preparation, poll, check, and close callbacks. Each phase handles specific tasks, and the loop continues until there are no more tasks to perform. For example, during the timers phase, the event loop executes callbacks for setTimeout() and setInterval(). By handling tasks asynchronously, the event loop ensures non-blocking execution, making Node.js capable of handling thousands of requests simultaneously.
32. What are worker threads in Node.js?
Worker threads in Node.js are designed to allow parallel execution of JavaScript code by running it in separate threads. This feature is especially useful for handling CPU-intensive tasks such as cryptographic operations, data processing, or image manipulation, which can otherwise block the event loop and slow down the performance of Node.js applications.
By default, Node.js uses a single-threaded event loop, which is highly efficient for I/O-heavy tasks, but it struggles with tasks that require significant CPU time. Worker threads address this limitation by offloading heavy computations to different threads, allowing the main event loop to continue running without interruption.
Each worker thread runs in isolation from others, but they can communicate through message-passing mechanisms such as parentPort.postMessage() and worker.on('message'). Worker threads enable developers to achieve parallelism in Node.js, improving performance in scenarios that involve resource-intensive tasks.
33. Explain the concept of middleware in Node.js.
Middleware refers to functions that have access to the request (req), response (res), and the next() function in the request-response cycle of a Node.js application. Middleware can execute any code, make changes to the req and res objects, and end the request-response cycle or pass control to the next middleware in the stack using the next() function. Middleware functions are widely used in frameworks like Express.js for tasks such as parsing request bodies, managing sessions, handling errors, logging requests, and authentication. Properly structured middleware helps in creating modular and maintainable applications.
34. What is the difference between fork() and spawn() in Node.js?
Feature
fork()
spawn()
Purpose
Creates a new Node.js process with IPC (Inter-Process Communication) for communication between parent and child processes.
Used to create a new process to execute external commands or system-level operations.
Memory Sharing
Shares memory with the parent process.
Does not share memory with the parent process. Each process is independent.
Communication
Communicates using IPC channels. Ideal for parallel tasks that need to share data between processes.
Uses standard input/output (stdout, stderr) streams for communication.
Use Case
Best for creating worker processes in Node.js to scale across multiple CPU cores.
Suitable for executing shell commands or running external programs.
Output Handling
Does not directly return stdout or stderr. Communication happens via IPC messaging.
Returns stdout and stderr streams for reading the command’s output directly.
Execution Context
Specifically designed for spawning new Node.js processes.
Can be used to spawn any system command, not limited to Node.js processes.
Performance
Slightly heavier due to additional overhead of IPC communication and memory sharing.
More lightweight when executing external commands.
35. What is the purpose of the 'domain' module in Node.js?
The domain module in Node.js was designed to handle multiple different I/O operations and their errors within a single context. It allows developers to group related I/O operations and handle exceptions thrown from any of them. By doing so, it prevents the application from crashing due to unhandled exceptions. However, the domain module is deprecated and is no longer recommended for use. Modern alternatives like Promises, async/await, or using structured error-handling mechanisms in frameworks such as Express have replaced the need for the domain module.
Node.js MCQ
36. What is the default scope of Node.js modules?
A) Global
B) Local
C) Shared
D) Private
Answer: B) Local By default, Node.js modules have a local scope, meaning variables, functions, and objects declared within a module are not accessible outside that module unless explicitly exported.
37. Which of the following is true about process.nextTick()?
A) It executes in the I/O cycle of the event loop
B) It executes after setTimeout()
C) It executes before any I/O operation
D) It executes at the end of the event loop
Answer: C) It executes before any I/O operation process.nextTick() ensures that the callback is invoked before any I/O events, making it useful for deferring operations within the same tick of the event loop.
38. What does the Buffer class in Node.js do?
A) Handles large JSON data
B) Handles binary data directly
C) Handles large string operations
D) Handles system operations
Answer: B) Handles binary data directly The Buffer class in Node.js is used for working with binary data streams in an efficient way.
39. Which method is used to stop a Node.js server?
A) server.close()
B) process.exit()
C) server.stop()
D) killServer()
Answer: A) server.close() The server.close() method is used to stop the server from accepting new connections while keeping existing connections open until they finish.
40. Which module is required to create an HTTP server in Node.js?
A) fs
B) http
C) url
D) net
Answer: B) http The http module is required to create an HTTP server in Node.js, enabling it to handle HTTP requests and responses.
41. How does Node.js handle file operations?
A) Sequentially
B) Synchronously
C) Asynchronously
D) Using threading
Answer: C) Asynchronously Node.js performs file operations asynchronously by default, which improves performance in I/O-heavy applications.
42. What does the exports object do in Node.js?
A) Imports other modules
B) Exports functions or objects to make them available outside the module
C) Provides a buffer for data streams
D) Encodes URL data
Answer: B) Exports functions or objects to make them available outside the module The exports object in Node.js allows you to define which parts of a module are accessible to other parts of the application.
43. Which of the following statements is true about the event-driven model in Node.js?
A) Node.js blocks the main thread during I/O operations
B) Node.js uses threads for handling I/O
C) Node.js uses a single thread and non-blocking I/O operations
D) Node.js only handles synchronous code
Answer: C) Node.js uses a single thread and non-blocking I/O operations Node.js operates on a single-threaded event loop model, handling I/O operations asynchronously, which allows it to handle multiple requests efficiently.
44. Which of the following is used to parse the URL in Node.js?
A) fs
B) path
C) url
D) querystring
Answer: C) url The url module in Node.js is used to parse, resolve, and manipulate URLs.
45. What command is used to install a package globally in Node.js?
Node.js is an Open source, cross-platform web application JavaScript runtime environment. It is used in traditional websites and backend API services.
Is Node.js frontend or backend?
It is a common misconception among developers that they think Node.js to be a backend framework and is only used for building servers. But in reality, Node.js can be used both on the frontend and backend.
Is Node.js a framework?
Node.js is not a framework or library. It is a runtime environment built on Google chrome’s V8 JavaScript engine.
Is Node.js a programming language?
Node.js is not a programming language, but it allows the developers to use JavaScript, a programming language.
Conclusion
In this article, we provided a comprehensive overview of essential Node.js interview questions. We began with a brief introduction to Node.js, followed by detailed and frequently asked interview questions, each accompanied by clear and accurate answers to help you prepare effectively.
We hope that this blog has helped you enhance your knowledge regarding Node.js Interview Questions, and if you would like to learn more, you can also consider our Interview Preparation Course.