Listed below are 15 of probably the most regularly requested questions on Node.js interviews

Do you have a programming interview? Preparing for this is as important as developing your coding knowledge to improve it. It gives you the confidence to conduct the interview and shake off the nervousness. This is especially true if this is your first time in your life before a programming interview.

To give the Node.j developers the necessary preparation for an interview, I’ve put together a list of 15 frequently asked questions about Node.js and web development interviews. These questions and their answers will also encourage you to brush up on any areas that you think need improvement before the big interview.

In this post, we will focus on questions that are specific to Node.js only. Note, however, that questions about Javascript are very common in Node.j’s interviews. You should therefore prepare yourself for some of these questions as well. We wrote a post not so long ago Common JavaScript Interview Questions to cover the basics.

Now let’s take a look at the knot-related questions you are likely to ask in your next interview.

How is Node.js different from Javascript?

When should you use Node.js?

Node.js is asynchronous, event-driven, non-blocking and single-threaded. This makes Node a perfect candidate for developing the following types of applications:

  • Real-time applications such as chat and services that provide live updates.
  • Streaming applications that deliver video or other multimedia content to a large audience.
  • I / O intensive applications such as collaborative platforms.
  • Web backends that follow the microservices architecture.

However, the unique properties of Node.js make it less than ideal for some other types of applications: Those who perform CPU-intensive tasks like complex math calculations are constrained by Node’s single-threaded execution.

If you want to learn more about it, check out our article on the architecture of Node.js and when you can use Node.js in projects.

What does EventEmitter do?

Every object in Node.js that can output events is a member of the EventEmitter Great. The The http module is one such example.

All EventEmitter Classes can use that eventEmitter.on () function to attach event listeners to the event. As soon as such an event is caught, its listeners are called one after the other synchronously.

What is Node’s event loop?

Because Node.js is single-threaded, it doesn’t have to be blocking to prevent the thread from taking too long to do a task that takes a while to complete. The event loop is responsible for enabling this non-blocking behavior. His job is to plan pending tasks using the application thread.

We know that Node uses callbacks to process the response returned by an asynchronous function when its task is complete. Similar to the event that created the task, an event is also issued when the task completes. Node.js adds these events that need to be handled to an event queue.

The event loop loops through events in the event queue and schedules when the associated callback functions should be performed.

What are nodal currents?

Streams are pipelines that read or write data from a source and transmit it to a continuous flow destination. There are four types of streams:

  • Readable
  • Writable
  • Duplex (both readable and writable)
  • Transform (A kind of duplex stream. The output is calculated from the input.)

Every stream is also a EventEmitter. This means that a stream object can throw events when there is no data in the stream, when data is available in the stream, or when data in the stream is deleted from the program.

What is the difference between the readFile and createReadStream functions?

The readFile function Asynchronously reads the entire contents of the file and stores it in memory before passing it to the user.

createReadStream Uses a readable stream that reads the file block by block without storing it entirely in memory.

createReadStream optimizes the file reading process compared to readFile by using less memory and doing it faster. If the file is of a considerable size, the user does not have to wait long for all of the content to be available because small blocks are sent to the user as it is read.

How do you deal with unrecorded exceptions in Node.js?

We can catch uncaptured exceptions that are thrown in the application at the process level. We add a listener to that process global object to capture such events.

Can Node take full advantage of a multiprocessor system?

Node applications are always single-threaded. Therefore, of course, the application only uses a single processor even when running on multiprocessor systems.

One of Node’s core modules, Cluster, provides support for Node applications to take advantage of multiple cores. It allows us to create multiple worker processes that can run on multiple cores at the same time and share a single port to listen for events.

Here each process uses IPC to communicate with the main thread and to pass the server handle to others as needed. The master process can either listen on the port itself and hand each new connection to child processes in a round robin order, or assign the port to child processes so that the child processes can listen to requests.

What reactor design pattern is used in Node.js?

The reactor pattern is used to maintain non-blocking I / O in Node.js. It adds a callback function (handler) to every I / O operation. The handler is then passed to a demultiplexer when the request is generated.

Demultiplexer collects every I / O request made in the application and queues them as events in a queue. We call this the event queue. After the event queues, the demultiplexer returns control of the application thread.

In the meantime, the event loop loops through each event in the event queue and invokes the attached callback to process the event response.

This is the reactor pattern used by Node.js.

What are the advantages of a single threaded web backend versus a multi-threaded backend?

In other words, although Node is single-threaded, most of the programming languages ​​used for backend development provide multiple threads for application operations. How is it beneficial for backend development to only have a single thread?

  • It’s easier for developers to implement applications. Our applications have no risk of suddenly encountering unexpected racing conditions during production.
  • Single threaded applications are easily scalable.
  • You can service a large number of user requests that come in at the same time without much delay. In comparison, a multithreaded backend has to wait until a thread from the thread pool is free to service the user request when the traffic is high. Because Node is non-blocking, there is no risk that a user request will hang too long on the individual thread (this only applies if the operations are not CPU intensive).

What is REPL in the node?

REPL stands for Read-Eval-Print-Loop. It is a virtual environment in which you can easily run a programming language. The node has a built-in REPL for executing JavaScript code. It is similar to the consoles we use in browsers to run JavaScript code.

To start the REPL node, all you need to do is run the node command on the command line. Once you’ve written a line of JavaScript code, you can then see its output.

The callback passed to the setImmediate function is executed through the event queue in the next iteration of the event loop.

On the other hand, the callback was forwarded to process.nextTick is executed before the next iteration of the event loop and after the operation currently running in the program has been completed. When the application starts, the callback is invoked before the event loop iterates over the event queue.

Therefore the process.nextTick call back is always called before the setImmediate callback.

What are stubs?

Stubs are used when testing applications. They simulate the behavior of a specific component or module so that you can focus only on the part of the code that you want to test. By using stubs instead of components that are not relevant to the test, you don’t have to worry about external components affecting the results.

For example, if the component under test is doing a file read before the part under test, you can use a stub to simulate this behavior and return bogus content without actually reading the file.

In Node we use libraries like Sinon for this purpose.

Why is it advisable to separate “App” and “Server” in Express?

By separating the app and server in Express, we can separate the API implementation from the network-related configuration. This allows us to run API tests without making network calls. This also guarantees faster test execution and better metrics for code coverage.

To achieve this separation, you should declare API and server in separate files. Here we use two files: app.js. and server.js.

What are yarn and npm? Why would you want to use yarn over npm?

Above the sea level is the standard package manager distributed with Node.js. It has a large library of public and private packages stored in a database called “emp registry” that users can access through npm’s command line client. Using npm, users can easily manage dependencies used in a project.

yarn is also a package manager released in response to some of npm’s shortcomings. However, yarn relies on npm registration to give users access to packages. Since the underlying structure of the yarn is based on npm itself, your project structure and workflow will not need to experience significant changes when you migrate from npm to yarn.

As I mentioned earlier, in some cases, yarn offers better functionality over npm. Unlike npm, all downloaded packages are cached so you don’t have to download them again when needed.

It also provides better security by using checksums to verify the integrity of packets. It guarantees that a package that worked on one system will work the same on every other system.


In this post, we’ve worked through 15 of the most frequently asked questions about Node.js interviews so you can better prepare for your next interview. When you know what kind of questions you are likely to be asked and their answers, you can be confident of answering interview questions without feeling nervous.

These items was originally published on Live code stream by Juan Cruz Martinez (Twitter: @bajcmartinez), Founder and publisher of Live Code Stream, entrepreneur, developer, author, speaker and maker of things.

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