NodeJS: Top 14 Interview Questions & Answers (2023)

Juan SalasJuan Salas

Juan Salas

NodeJS: Top 12 Interview Questions (2023)

NodeJS is a widely used JavaScript framework for back-end development, which creates a high demand for developers familiar with its use. Properly preparing for an interview related to this type of position is essential for hiring talent and applying to development positions.

Here are the 15 most common interview questions on NodeJS and some insights on preparing for them.

1. What Is NodeJS?

NodeJS is an open-source, cross-platform, JavaScript runtime environment that executes JavaScript code outside of a browser. Node lets developers use JavaScript to write command line tools and for server-side scripting—running scripts server-side to produce dynamic web page content before the page is sent to the user's web browser.

It is an event-driven architecture that supports asynchronous I/O, allowing for concurrent requests to be processed without blocking any single request. Node provides a comprehensive library of JavaScript modules that significantly simplifies the development of web applications.

Node offers an easy way for developers to create real-time applications such as chat apps, online games, and collaborative tools like wikis or group calendars.

NodeJS also enables developers to quickly build efficient backends for web and mobile applications by providing them with access to powerful APIs and database integrations such as MongoDB, Redis, Elasticsearch, etc.

Because of its lightweight nature and scalability, NodeJS may also be utilized to construct IoT (Internet of Things) projects.

2. What Are NodeJS Modules?

Modules are groups of linked functions that are loaded into the code as a single file. They are similar to JavaScript libraries. Modules can be organized into packages.

3. How Does NodeJS Handle Asynchronous Programming?

NodeJS uses an event-driven, non-blocking I/O model to enable asynchronous programming. This means that it can handle multiple requests simultaneously without waiting for one request to finish before starting the next.

It can do this by using a single thread to process all requests at once, which makes it much more efficient than other web servers that require multiple threads for each request.

NodeJS offers many useful libraries and features for asynchronous programming, such as promises, async/await, and generators. These features make it easier for developers to write code that handles asynchronous tasks without manually managing callbacks or tracking state changes between different application parts.

Asynchronous programming in NodeJS can be used in many scenarios, such as handling user input from forms or making API calls from within the application.

4. What Is An Event Loop?

An event loop in NodeJS is a mechanism that allows the server to perform non-blocking I/O operations. It works by allowing the server to register events and then execute a callback function when an event occurs. In this way, the server can continue to accept requests while waiting for an event to occur.

The event loop is based on the JavaScript language so that it can be used with any application built with NodeJS.

The event loop consists of the following components:

  • The task queue: stores functions that have been registered as callbacks for events that have occurred.
  • The timer queue: stores functions scheduled to run after a certain amount of time has elapsed.
  • The poll queue: contains functions waiting for an I/O operation to complete before they can be executed.

5. What Is A Callback, And How Do They Work?

A callback is a function passed as an argument to another function and executed after the outer process has been completed.

For asynchronous programming, this means that code can be performed without waiting for other parts of the program to finish executing.

Callbacks are used extensively in NodeJS due to their asynchronous nature.

When a callback is used, the outer function will execute and then pass control back to the inner function (the callback). The callback will then run with whatever data was returned from the outer function. This allows multiple tasks to be run simultaneously rather than having them happen one after another.

Callbacks are essential for ensuring that code runs efficiently and asynchronously in NodeJS. Without callbacks, programs would have to wait for each task to be complete before moving on to the next one, which could cause delays and make applications less responsive.

Callbacks allow developers to write code that can handle multiple tasks and respond quickly when needed.

6. What Is the Difference Between Callbacks and Promises?

Callbacks are integral components of the same task in the event loop's sequence, guaranteeing that the value of the inner function is accessible to the outer function when it is executed.

Promises are representations of data that may become available at a later time. Promises enable the event loop to proceed through its sequence while waiting for an asynchronous evaluation of the promise.

7. How To Debug A NodeJS Application?

There are various methods for debugging a NodeJS application. The most common way is to use an integrated development environment (IDE) such as Visual Studio Code or WebStorm to debug the code.

This allows devs to set breakpoints, step through the code line by line, and inspect variables.

Another method is using the Node Inspector, a debugging tool built into NodeJS. With it, devs can connect the application to a debugger, view the source code, set breakpoints, and step through the code.

Developers can also use console.log() statements throughout their code to print out values of variables at different points in the execution of their program.

Finally, they can use a third-party debugging tool such as Chrome DevTools or Firebug for Firefox to inspect and debug your NodeJS application.

8. What Is npm, And Why Should Developers Use It?

npm stands for Node Package Manager, a package manager for JavaScript. It makes it easy for developers to reuse existing code and create new projects quickly and efficiently.

npm is the world's largest software registry, containing over 1 million packages of reusable code. These packages are used by millions of developers around the world to build their applications more quickly.

It also provides a command line interface (CLI) which allows developers to install, update, configure, and uninstall packages from the command line.

Using npm can save developers time by allowing them to use existing code instead of writing everything from scratch. This means that developers can focus on building the needed features without worrying about reinventing the wheel each time they want to add a feature or fix a bug.

Additionally, npm helps ensure that all projects use identical versions of dependencies so that there are no conflicts between different versions of code being used in other projects.

9. How Can You Secure A Web Application Built With NodeJS?

Securing a web application built with NodeJS requires developers to take the necessary steps to ensure their application is not vulnerable to common security threats.

They should use secure coding practices, such as input validation and output encoding, to prevent malicious code from executing on the server.

Additionally, developers should use authentication and authorization mechanisms to protect data from unauthorized access. They should also implement encryption protocols, such as TLS/SSL, to protect data in transit.

10. What Are Some Differences Between Client-Side JavaScript And Server-side JavaScript When Using NodeJS?

Client-side JavaScript is the code that runs in the browser, while server-side JavaScript is the code that runs on the server. Node allows developers to use JavaScript for both client-side and server-side development.


  • Runs in a web browser.
  • Used for UI design, form validation, animation, and AJAX requests.
  • Executed by a user's computer/browser.


  • Runs on a web server or application server.
  • Used for database access, business, logic, and application logic.
  • Executed by an application server or web server running NodeJS.

11. How Can You Test A NodeJS Application?

There are several ways to test a NodeJS application, including unit testing, integration testing, and end-to-end testing.

Unit tests

Unit tests are used to test individual components of the application in isolation from other members. It enables developers to rapidly find problems with certain areas of the codebase without having to build up a full testing environment. Unit tests can be written using frameworks such as Jest and Mocha.

Integration tests

Integration tests are used to ensure that different application components work together correctly. By setting up an environment similar to production, these tests can detect issues with data flow between parts or unexpected behavior in specific scenarios. Integration tests can be written using frameworks such as Chai and SuperTest.

End-to-end tests

End-to-end (E2E) tests are used to test the entire system from start to finish, simulating user interactions with the application and checking that they result in the expected outcome. E2E tests can be written using frameworks such as Cypress and TestCafe.

Manual tests

Manual testing involves running through scenarios and checking for bugs or unexpected behavior that automated tests may not have detected.

12. How Can You Monitor The Performance Of A Production-Level Application Built with NodeJS?

Several tools are available to help monitor the performance of a NodeJS application. These include:

1. Application Performance Monitoring (APM) tools

Tools such as New Relic and AppDynamics offer detailed insights into application performance metrics such as response times, throughput, errors, and more.

2. Logging tools

LogDNA or Splunk can track and analyze log data from the NodeJS application to identify potential issues.

3. Profiling tools

Developers can use Node Inspector or Chrome DevTools to observe how their code executes in real-time and identify potential bottlenecks.

4. System monitoring tools

Datadog or Prometheus provides insights into system resource utilization (CPU/memory/disk) and can detect any unexpected usage spikes that could lead to performance issues.

13. Why Does Google Utilize The V8 Engine for Node?

Due to its open-source nature, Google's V8 is the most advanced and quickest JavaScript and WebAssembly engine to date, which allows for a large community of developers to build features and address issues. It is also highly adaptable to nearly any machine.

14. What Are Forks In The Node Context?

The fork command is a subset of the spawn command that creates a new instance of the V8 engine on which NodeJS runs, allowing the parent and child processes to interact. This is important for building a worker pool to utilize multi-core processors and convey individual messages across processes more efficiently.

In Conclusion

NodeJS is a popular environment, but it must be used correctly. Developers need to understand how it fits in with the rest of a development stack.

The questions in this article are basic in terms of using NodeJS. We must ensure that the talent thoroughly understands this material and can describe it in their own words.