Node.js Interview Questions with Answers

Are you a Node.js Developer seeking a job in one of the top US MNCs? Or, are you a recruiter from a top US MNC looking for an excellent Node.js Developer? In either case, you have landed on the right page.

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When Node Js first launched in 2009, it quickly became the go-to option for web applications. Node Js made developing, deploying, and maintaining web applications easier with its event-driven architecture and non-blocking I/O model. Today, companies of all sizes, including the likes of Netflix, PayPal, and LinkedIn use Node Js. Understandably, Node Js developers are in high demand.

This article covers the most commonly asked Node Js interview questions and answers to help you hit the ground running. We will cover questions ranging from Node Js fundamentals to its more advanced features.

What is a Node js Developer:

Node Js developers are IT professionals responsible for designing, developing, and testing Node Js applications. Node Js developers typically work on web applications that leverage Node Js frameworks, such as Express.js and Sails.js. They handle Node Js development tasks like API integration, server configuration, debugging, and unit testing.

Node js Developer Qualifications

Hiring Node Js developers requires a keen eye for Node Js qualifications. Node Js developers should have the following minimum qualifications:

  • Bachelor's degree in Information Technology or Computer Science
  • Some years of experience working with Node Js
  • Experience developing Node Js applications with Node Js frameworks
  • Proficiency with Node Js databases, web servers, and cloud platforms
  • Knowledge of Node Js package managers and build tools
  • Strong understanding of Node Js concepts, such as asynchronous programming and event-driven architecture
  • Excellent debugging and troubleshooting skills
  • Strong analytical and problem-solving skills
  • Good communication and collaboration skills

Additionally, Node js developers are often required to have a working knowledge of the following:

  • Node js frameworks such as Express and Hapi
  • Node js databases such as MongoDB and CouchDB
  • Node js web servers such as Apache and Nginx
  • Node js cloud platforms such as Amazon Web Services and Azure
  • Node js package managers such as NPM and Yarn

What Does a Node js Developer Do

It's important to understand the roles and responsibilities of Node Js developers so you can make sure they have what it takes to excel in their role and also ask relevant Node Js interview questions. Generally, Node Js developers have the following roles and responsibilities:

  • Developing and maintaining all server-side network components
  • Integrating user-facing web components with server-side logic
  • Designing and developing web applications using Node Js frameworks
  • Writing efficient code that follows best practices
  • Testing web applications and debugging errors
  • Optimizing web application performance
  • Collaborating with front-end developers to ensure web applications are properly integrated
  • Maintaining web servers and databases
  • Updating web applications as needed with new features, security patches, and bug fixes

Node js Interview Questions with Answers

Let's dive into Node Js interview questions and answers. We'll discuss these questions in three categories:

  • Junior/ Entry-level/ Fresher
  • Mid-level/ Intermediate
  • Senior/ Advanced

Junior Node Js Interview Questions

These Node Js interview questions are for candidates starting out in web development and Node Js. They may have just cleared college or be in the early stages of their web development career.

What is Node Js?

Node Js is a JavaScript-based programming language that allows web developers to build web applications. It's an open-source runtime environment powered by the Google Chrome V8 JavaScript engine and uses a non-blocking I/O model and event-driven architecture.

What is the purpose of Node Js?

Node Js enables web developers to create web applications quickly and easily. It provides an event-driven, non-blocking I/O model for web applications. Additionally, Node Js makes it easier to manage web application resources because of its  asynchronous programming features. It also supports web sockets and other web technologies, making web development easier.

What do you understand by the term I/O?

I/O stands for Input/Output. It is the process of reading and writing data to a computer system. Node Js uses a non-blocking I/O model, which allows developers to read and write data asynchronously. This means that the Node Js application can continue to process tasks even when waiting for a response from an external system.

What makes Node.js superior to other popular frameworks?

Node Js is faster and more efficient than other popular frameworks because of its  v8 engine. The v8 engine compiles and executes JavaScript code faster than other frameworks, making Node Js applications run faster. Additionally, Node Js is single threaded, meaning it can handle more simultaneous requests than other frameworks. This makes Node Js more efficient and cost-effective to run.

In JavaScript, what is a first-class function?

In JavaScript, a first-class function is a function you can treat as any other value in the language. Developers can pass it as an argument, store it in a variable, or return it from a function. This function reduces code duplication by allowing developers to write modular code that they can reuse.

What is asynchronous programming?

Asynchronous programming is a programming technique where the program does not need to wait for a task to complete before continuing with the execution of instructions. This enables applications to process multiple tasks in parallel, thereby improving the application's performance.

What does REPL stand for?

REPL stands for Read Eval Print Loop. It is a type of interactive programming interface that evaluates user input and prints the result. This allows developers to quickly test small pieces of code without having to write a complete program.

What is the event loop in Node Js?

The event loop in Node Js is a mechanism that enables Node Js to process multiple tasks in parallel. It consists of an event queue for storing incoming requests, file changes, or input from an API. The event loop then processes these events in a non-blocking manner, allowing Node Js applications to take advantage of its asynchronous programming features.

What are the read write operations in Node Js?

The read/write operation in Node Js enables developers to read and write data from files on the server. This operation reads and writes data from a file, creating, updating, and deleting files.

Mid-level Node Js Interview Questions

These Node Js interview questions are for candidates who are more experienced with Node Js. They may have a few years (3-5 years) of experience working with Node Js and be familiar with some more advanced web development concepts.

What is the HTTP module in Node Js?

The HTTP module in Node Js handles HTTP requests and responses. It provides an interface to create web servers and make http calls to web APIs. The HTTP module is also responsible for parsing requests and providing methods to send data over the web. Additionally, the http module provides several other useful functions, such as creating web sockets, establishing secure connections, and more.

In Node.js, how would you use a URL module?

The URL node module enables developers to parse URLs into its component parts. It provides methods to extract query parameters, pathname, path, hostname, port, and other URL components. The URL module can also create URLs from its component parts.

What is an asynchronous callback?

An asynchronous callback is a function that is executed after an asynchronous operation completes. When the asynchronous operation returns a result, it triggers this function to perform additional tasks.

What is command line, and how do you use it in Node Js?

The command line is a text-based user interface used to execute commands in a command-line interface (CLI). It is commonly used to execute tasks such as running scripts and working with files. In Node Js, the command line can run scripts, install packages, and more.

What is a package manager?

A package manager is a command-line utility used to install, update and remove software packages. Node Js comes with two package managers: NPM and Yarn.  NPM installs packages from the command line, while Yarn automates package installation by managing a list of dependencies.

What is the eventemitter class in Node Js?

The event emitter class in Node Js is a utility that enables developers to listen for and emit events. It creates event handlers that can be triggered when an event occurs. This event emitter class is used in Node Js event-driven applications, such as event-driven web servers and event-based APIs.

What does the var HTTP require HTTP command do in Node Js?

The var HTTP require HTTP command is used to import the http module into a Node Js application. This command creates an instance of the http class, which provides methods and properties to create web servers and handle HTTP requests.

What are the different types of streams in Node Js?

The different types of streams in Node Js are readable, writable, and duplex. The readable stream is used for reading data from a source. On the other hand, the writable stream is used for writing data to a destination while the duplex stream is used for reading and writing data simultaneously.

Advanced Node Js Interview Questions

These are Node Js interview questions for applicants with 5 years of experience or more. These candidates should be familiar with Node Js concepts and be able to handle advanced development tasks.

What is the difference between a callback and a promise in Node Js?

Callbacks are functions used to handle asynchronous operations. In contrast, promises are objects that represent the result of an asynchronous operation.

What are the benefits of using promises instead of callbacks?

Promises improve the readability and maintainability of code by eliminating the "callback hell" issue. Promises are object-oriented, making it easier to debug and test code. Additionally, promises can be chained together for better control flow and error handling. Finally, promises make asynchronous programming easier by managing asynchronous operations in a single place. Finally, streams support asynchronous programming and enable developers to return data without waiting for the entire process to complete.

What is the purpose of try/catch in Node Js?

The try/catch block in Node Js handles errors or exceptions. It allows developers to execute code that might throw an error and then handle the error if it occurs. This makes debugging and testing code much easier, as developers can catch errors and handle them in a single place.

What differentiates Node.js's fork() and spawn() methods?

The fork() method in Node Js creates a new process that is a copy of the existing one. It has access to all the same variables and functions as the existing process. On the other hand, the spawn() method creates a new process separate from the existing one. The spawn() method does not have access to the same variables and functions as the existing process, but it runs faster than the fork() method.

In Node.js, how do you open a file?

You can open a file in Node Js using the  fs.open() method. This method takes two arguments: a filename and a flag that specifies how to open the file. The fs.open() method returns a file descriptor used to read, write, and close the file.

Which HTTP requests does Node Js support?

Node Js supports the HTTP GET, POST, HEAD, and DELETE requests.

  1. The GET request retrieves data from a server.
  2. The POST request sends data to a server.
  3. The HEAD request retrieves headers from a server.
  4. The DELETE request deletes data from a server.

What are the benefits of using streams in Node Js?

Streams simplify data processing by allowing developers to process data in chunks. This reduces memory usage, improves performance, and allows faster data transfer. Additionally, streams can pipe data from one stream to another, making it easier to manage data flows.

What is the purpose of process.nextTick in Node Js?

The process.nextTick command in Node Js is used to schedule a callback function to be executed as soon as possible. This command can defer a callback until the current execution context is finished. It is commonly used to ensure asynchronous operations are executed in the correct order.

What is the purpose of a cluster in Node Js?

The cluster module in Node Js enables developers to create multiple processes or threads that can be used to take advantage of multiple CPU cores. This allows Node Js applications to scale more efficiently and improves their performance.

What is v8 heap?

The v8 heap is the memory space allocated by the v8 JavaScript engine for storing objects and variables. v8 uses this memory space to store all the data associated with a Node Js application, including variables, objects, and function calls. v8 is optimized to reduce memory usage and improve the performance of applications. The v8 heap is an important part of Node Js and must be managed properly to ensure applications run efficiently. Developers should monitor v8 heap usage and tune their applications for optimal performance. Additionally, v8 provides several performance-related flags to help developers better manage v8 heap usage.

What is garbage collection in Node Js?

Garbage collection is a process used by v8 to reclaim memory from unused objects and variables. v8 uses garbage collection algorithms to determine which parts of v8 heap can be released and reclaimed. v8 runs garbage collection periodically, so developers should ensure their applications use v8 resources efficiently to minimize garbage collection occurring. This improves the performance of Node Js applications. Garbage collection can also be manually triggered by calling the v8.gc() method. This can be used to force garbage collection and reclaim memory when needed.

What are the different types of errors in Node Js?

The different types of errors in Node Js include syntax errors, runtime errors, and logical errors. Syntax errors occur when the code does not conform to the syntax of the language. Runtime errors occur when a program is executing and an unexpected error occurs. Logical errors occur when the written code is correct but produces an incorrect result. Developers can debug and test these errors using the Node Js error handling functions. These include try/catch blocks, the error-first callback pattern, and Promises.

Hire a Node Js Developer

Hiring a Node Js developer to join your team requires a comprehensive understanding of the Node Js platform and expertise in web development. This can be a difficult process due to the technicalities involved. That’s why you should let a professional handle the interview process so that they can ask relevant Node Js interview questions.

At Revelo, we provide businesses with access to top-tier Node Js developers with the experience and skills necessary to take on any web development project. We match you with talent who become full-time hires and are embedded in your team. Our pool of talented Node Js developers has the knowledge and expertise to create robust web applications that meet the needs of your business.  Contact us today to learn more about how we can help you hire the perfect Node Js developer for your team.

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