Top 20+ Node.js Interview Questions and Answers for 2022

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 Node.js is a super popular server-side platform that is being used by more and more organizations. If you're preparing for a career change and have an upcoming job interview, it's always a good idea to prepare ahead of time and brush up on your interview skills. Although there are several common Node.js interview questions that appear in all types of interviews, we also recommend that you prepare by focusing on exclusive questions related to your specific industry.
We've compiled a comprehensive list of common Node.js interview questions that come up frequently in interviews and the best ways to answer them. This will also help you understand the basic concepts of Node.js.

Node.js interview questions and answers for beginners

This section will provide you with basic Node.js interview questions that will especially help newbies.

1. What is Node.js? Where can you use it?

Node.js is an open-source cross-platform JavaScript runtime and library for running web applications outside the client browser. It is used to create server-side web applications.
Node.js is ideal for data-intensive applications because it uses an asynchronous, event-driven model. You can use I/O intensive web applications such as video streaming sites. You can also use it to develop: real-time web applications, network applications, general purpose applications, and distributed systems.

2. Why use Node.js?

Node.js makes it easy to build scalable network programs. Some of its benefits include:
  • He is generally fast
  • It rarely blocks
  • It offers a uniform programming language and data type
  • Everything is asynchronous
  • It provides great concurrency

3. How does Node.js work?

A web server using Node.js typically has a workflow that is very similar to the diagram below. Let's explore this operation flow in detail.

Clients send requests to the web server to interact with the web application. Requests can be non-blocking or blocking:
  • Querying data
  • Deleting data
  • Update data
  • Node.js fetches incoming requests and adds them to the event queue
  • Requests are then passed one at a time through an event loop. It checks that the requirements are simple enough to not require any external resources
  • The event loop processes simple requests (non-blocking operations) such as I/O Polling and returns responses to the corresponding clients.
One thread from the thread pool is assigned to one complex request. This thread is responsible for completing a specific blocking request by accessing external resources such as compute, database, file system, etc.
Once the task is complete, a response is sent to the event loop, which sends it back to the client.

4. Why is Node.js single-threaded?

Node.js is single-threaded for asynchronous processing. By performing asynchronous processing on a single thread under typical web load, higher performance and scalability can be achieved instead of a typical thread-based implementation.

5. If Node.js is single-threaded, how does it handle concurrency?

The multi-threaded stateless request/response model is not followed by the Node JS platform and adheres to the single-threaded event loop model. The Node JS Processing paradigm is heavily influenced by JavaScript's event-based model and JavaScript's callback system. This allows Node.js to easily manage multiple concurrent client requests. The event loop is the heart of the processing model in Node.js.

6. Explain callback in Node.js.

A callback function is called after the specified task. It allows other code to run in the meantime and prevents any blocking. As an asynchronous platform, Node.js relies heavily on callbacks. All Node APIs are written to support callbacks.

7. What are the advantages of using promises instead of callbacks?

The control flow of asynchronous logic is more specified and structured.
The clutch is low.
We have built in error handling.
Improved readability.

8. How would you define the term I/O?

The term I/O is used to describe any program, operation, or device that transfers data to or from a medium and to or from another medium.
Each transfer is an output from one medium and an input to another. The medium can be a physical device, a network, or files on a system. 

9. How is Node.js most frequently used?

Node.js is widely used in the following applications:

  • Real-time chats.
  • Internet of Things.
  • Complex SPAs (Single-Page Applications)
  • Real-time collaboration tools
  • Streaming applications
  • Microservices architecture

10. What is NPM?

NPM stands for Node Package Manager, which is responsible for managing all packages and modules for Node.js.

Node Package Manager provides two main functions:
Provides an online repository for node.js packages/modules that can be searched at search.nodejs.org
It provides a command-line tool for installing Node.js packages and also manages Node.js versions and dependencies

11. What is the .Exports module for?

In Node.js, a module encapsulates all related code into a single unit of code that can be analyzed by moving all relevant functionality into a single file. You can export a module with a module and export a function that allows it to be imported into another file with the necessary keyword.

12. Why is Node.js preferred over other backend technologies like Java and PHP?

Some of the reasons why Node.js is preferred include:
  • Node.js is very fast.
  • Node Package Manager has more than 50,000 packages available for developers.
  • Ideal for data-intensive, real-time web applications because Node.js never waits for an API to return data.
  • Better synchronization of code between server and client thanks to the same code base.
  • It is easy for web developers to start using Node.js in their projects because it is a JavaScript library.

13. What is meant by event driven programming?

14. What is an event loop in Node.js?
Event loops handle asynchronous callbacks in Node.js. It is the foundation of non-blocking I/O in Node.js, making it one of the most importEvent-driven programming uses events to trigger various functions. An event can be anything, such as a keystroke or a mouse click. A callback function is already registered with the element that will be executed whenever the event is fired.
ant environmental features.

15. Difference between process.nextTick() and setImmediate()?

Difference between method and product. This is achieved by using nextTick() and setImmediate(). next Tick() defers execution of an action until the next iteration of the event loop, or simply calls a callback function once the current execution of the event loop is complete, while setImmediate() executes a callback on the next event loop cycle and returns control to the event loop for any I /O operations.

16. What are the two types of API functions in Node.js?

The two types of API functions in Node.js are:
  • Asynchronous, non-blocking functions
  • Synchronous, blocking function

17. What are streams in Node.js?

Streams are objects that allow you to read data or write data continuously.
There are four types of streams:
  • Readable - Used for read operations
  • Writable − Used for write operations
  • Duplex – Can be used for both read and write operations
  • Transform – A type of duplex flow where the output is calculated based on the input.

18. What is callback hell?

Callback hell, also known as the pyramid of doom, is the result of heavily nested, unreadable, and unmanageable callbacks, which in turn make code difficult to read and debug.
incorrect implementation of asynchronous logic causes callback hell
19. What is reactor pattern in Node.js?
The reactor pattern is a concept of non-blocking I/O operations. This pattern provides a handler that is associated with each I/O operation. Once an I/O request is generated, it is sent to the demultiplexer

20. ​​Why does Google use the V8 engine for Node.js?

Developed by Google, the V8 engine is open-source and written in C++. Google Chrome uses this engine. Unlike other engines, V8 is also used for the popular Node.js runtime. V8 was originally intended to improve the execution speed of JavaScript in web browsers. Instead of using an interpreter, V8 converts JavaScript code to more efficient machine code to increase performance. It converts JavaScript code to machine code at runtime using a JIT (Just-In-Time) compiler, just like many current JavaScript engines such as SpiderMonkey or Rhino (Mozilla).

21. Explain the concept of middleware in Node.js.

Middleware is a function that receives request and response objects. Most of the tasks that middleware functions perform are:

Run any code
Update or modify the request and response objects
Complete the request-response cycle
Invoke other middleware on the stack

22. What are the different types of HTTP requests?

HTTP defines a set of request methods used to perform requested actions. Application methods include:
  • GET: Used to retrieve data
  • POST: Generally used to perform state change or reactions on the server
  • HEAD: Similar to the GET method, but requests a response without a response body
  • DELETE: Used to delete a predefined resource
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