Top 100 Node.js interview questions and answers in 2025

Exit codes are a collection of specific codes whose function is to complete a specific process. Examples of exit codes are fatal error, unused, internal JavaScript evaluation failure, etc.

Several factors can cause server latency and prevent scalability in Node.js. Some of the most common ones include:

• Blocking I/O: Blocking I/O operations can cause the server to become unresponsive while waiting for I/O operations to complete. This can be especially problematic in Node.js, which is designed to handle many concurrent connections. To avoid this, Node.js provides non-blocking I/O operations.
• Inefficient code: Inefficient code can cause unnecessary processing and slow down the server. This can be caused by poor algorithmic choices, excessive use of synchronous operations, or inefficient data structures.
• Insufficient hardware resources: Insufficient hardware resources, such as CPU, memory, or network bandwidth, can cause the server to become overloaded and unresponsive. This can be especially problematic in high traffic scenarios.
• Improper configuration: Improperly configured servers can cause performance issues. This can be caused by incorrect network settings, improper load balancing, or other misconfigurations.

Node.js uses the Google V8 JavaScript engine to convert JS code to C++.

Event programming is programming paradigm that uses events to trigger actions. An event can be generated by the user, by the system, or by the program itself.

Ajax is a client-side technology used to make web pages more interactive and dynamic, while Node.js is a server-side technology used to build scalable, high-performance web applications.

Non-blocking in Node.js means that the program can continue to execute other code even while waiting for I/O operations to complete.

Dependencies are present in the package.json file.

A control function manages and manipulates the flow of asynchronous code execution.

Node.js is designed to handle asynchronous I/O operations, which means that multiple I/O operations can be executed simultaneously without blocking the execution of other code. However, managing the flow of asynchronous code can be challenging, especially when multiple operations need to be executed in a particular order.

Control functions provide a solution to this problem by allowing developers to define the order in which asynchronous operations should be executed. They can be used to perform tasks such as error handling, callback management, and flow control.

Modularization in Node.js provides scalability when developing complex applications. The modularization option can be used to execute the import of objects, classes, functions, modules, and external files.

The call-back function is used to execute a function after a certain event has occurred.

Because of the event mechanism in Node.js, a callback function is called every time an event starts. This prevents blocking in Node.js.

There are three layers in the application architecture - API, service, and integration layers.

Two input arguments for asynchronous queue are concurrency value and task function.

No. Node.js applications do not buffer data.

The Boolean data type in Node.js can have one of two values: true or false.

It is possible to run external processes with Node.js. This can be done with the help of the child_process module.

It is possible to avoid callback hells by using promises; they can help to make the code more readable and easier to debug. You can also avoid callback hells using async/wait, libraries, and modularization.

The fs module is used to create and manipulate files. It also provides an API for interacting with the file system.

The os module provides a set of tools for interacting with the operating system. It provides an API for getting information about the system including memory, processor, file system, and network interfaces.

Duplex streams are both readable and writable. This means that they can be used to read data from a source and write data to a destination.

A transform stream is a type of stream that can be used to modify or transform the data as it is being read or written.

There are a total of 18 Node object methods available. These methods can be used to create, manipulate, and delete objects.

HTTP status code 504 indicates that the server is unable to process the request. This can be due to several reasons, such as an overloaded server or a network issue.

Routing is a process where you associate HTTP request to a URL path or specific routes. When a request matches one of these routes, a corresponding handling function is used. Routing is a robust mechanism that enables you to define how an application handles incoming requests.

A file can be opened in Node.js using the fs.open() method. This method takes two arguments, the path of the file and the flags.

Angular is a front-end web application framework. Node.js is a back-end runtime environment.

Node.js prevents bottlenecks and aids programmers in easily writing the code because of the single-thread model. Internally, there are several POSIX threads for different I/O operations like File, DNS, etc.

So, when Node receives an I/O request, it uses one of these threads for the I/O operation. Once the operation is complete, the result joins the event queue. Because of the event mechanism, the event loop starts after each event, checks the queue, and if Node’s execution stack is free, then the loop adds the queue result to it, thus managing concurrency.

Ctrl + C shortcut is used for terminating processes in Node.js.

A Node-Inspector is a debugging tool that allows developers to inspect and debug the code of an application through a graphical user interface.

The Dgram is an in-built module. It is useful in implementing UDP datagram packets.

You can import the buffer class without the buffer module.

The emit() function is used to fire an event.

In Node.js, a callback function is a function that is passed as an argument to another function and is called back at a later point in time. The purpose of using a callback function is to handle asynchronous operations.

In asynchronous programming, a function that initiates an asynchronous operation returns immediately while the operation continues in the background. When the operation is completed, the callback function is called with the result of the operation.

Yes, the middleware functions can execute code and they can modify the request or response objects.

There are four types of streams in Node.js: readable, writable, duplex, and transform.

Readable: The readable streams are used to read data from a specific source.

Writable: These streams are utilized for writing data to the destination.

Duplex: The duplex streams are used for both reading and writing data.

Transform: The transform stream enable the data to be transformed while it is being read or written. For example, you can use transform stream for data compression or data encryption as it is transmitted over the network.

The difference between setImmediate() and setTimeout() is that setImmediate() will execute the callback function immediately, while setTimeout() will wait for a specified time before executing the callback function.

Task function and concurrency value are the two arguments async.queue takes.

It is a special data type that only takes one value, i.e., null.

The difference between an event and a callback is that an event is a mechanism that signals a change or action that represents a part of the program's behaviour, while a callback is a function that takes data and sends it back to the calling function.

To delete a directory, we use fs. rmdir() method.

Yes, it is private and used internally.

Error-first callbacks are used to pass data and identify if an error has occurred.

Global objects are universal objects that are present in every module or file of the application without requiring explicit import statements.

In Node.js, a child process occurs when a new process is created using the child_process module. This module provides functionality to spawn child processes in a similar way to the fork() system call in Unix.

No, the let keyword can’t be redeclared and should be declared before use.

A control flow function controls the order in which code is executed. Usually, the code runs from the first line to the last line unless the structures (loops and conditions) changes the control flow.

module.exports is a Node.js module that allows you to export objects, functions, and variables from your code. You can use it to create modules that can be imported and used in other Node.js programs.

Libuv is a library that provides an event loop and a thread pool for handling asynchronous operations seamlessly. It helps in handling file systems, child processes, files, DNS, etc.

The express framework is a web application framework that helps you easily create server-side applications.

It is used when you want to disperse request processing over multiple Node.js processors. Mostly this is done to ramp up the ability to handle more requests per second.

Node.js uses cryptography for a variety of purposes, including password hashing, public key authentication, and encrypting network traffic. Some of the crypto modules used in Node.js are crypto, tls, crypto.createHash(), and crypto.createCipher() among others.

The important features of the npm directory are:

• A package.json file that defines the dependencies for your project
• A Node_modules directory that contains the modules for your project
• An .npmignore file that defines which files should be ignored while publishing your module

You can include an HTTP server in your Node module by using the http module. The http module provides an API for creating and interacting with HTTP servers and clients. It allows you to handle incoming HTTP requests and send HTTP responses, as well as control the server's behavior, such as listening on a specific port and setting various options.

The nmp -Ig-command installs the specific package for your project globally through npm which is the Node.js package manager.

You can scale a Node.js application by using a cluster. A cluster is a pool of worker processes that share a single port.

The process of connecting the output of one stream to another is called piping.

Punycode is a way of encoding internationalized domain names that use characters outside of the ASCII range.

The purpose of EventEmitter is to provide a mechanism for event-driven programming. The EventEmitter class provides a set of methods that allow you to emit events, listen for events, and remove event listeners. When an event is emitted, any listeners that are registered for that event will be invoked. This allows developers to write code that can respond to changes in state, user actions, or other events within the application.

The child process module allows you to spawn child processes in Node.js. The child process module provides a way to create and control child processes. A child process is a separate instance of the Node.js process that runs concurrently with the parent process.

The child process module allows you to spawn new child processes, execute commands in a shell, and communicate with child processes using IPC (Inter-Process Communication) channels.

This method returns a character at a particular index in a string.

The Split() function splits the string and returns an array of strings.

The simple way to do this is with help of the request library -