Top 70 Node.Js Interview Questions and Answers in 2021

Node.js is the open-source, cross-platform, back-end JavaScript runtime environment that runs on a V8 engine and executes the JavaScript code outside the web browser.

Node.js usually makes use of an event-driven, non-blocking I/O model that makes it efficient, and lightweight which is perfect for data-intensive real-time applications that run across the distributed devices.

Are you planning to attend a Node.js Interview? Are you in search of Node js Interview Questions and Answers? Then, you are on the right page. We have listed the most frequently asked Node.js Interview Questions and Answers.

Table of Contents

Top 70 Node.js Interview Questions

1. What are the advantages of Node.js?

Node.js make building scalable network programs easy. A few of its advantages include:

  1. Robust technology stack.
  2. Fast-processing and event-based model
  3. Scalable technology for microservices. 
  4. Rich ecosystem. 
  5. Strong corporate support. 
  6.  Seamless JSON support. 

2. Define the first-class function in Javascript?

A programming language can have First-class functions when the functions in that language are handled like any other variable. 

For example: In such languages, a function is passed as an argument to the other functions, and it can be returned by another function, and it can be assigned as a value to the variable.

3. What is Node.js?

Node.js can be defined as Server-side scripting used to build scalable programs. Its various advantages over the other server-side languages, the prominent one is being non-blocking I/O.

4. Explain how does Node.js work?

A web server using Node.js has a workflow.

  1. Clients usually send requests to webservers to interact with web applications. Requests can be either non-blocking or blocking:
  2. Querying for data
  3. Deleting the data 
  4. Updating  data
  5. Node.js retrieves incoming requests and adds them to the Event Queue.
  6. The requests are passed one by one via Event Loop. It checks whether the requests are simple enough and do not require any external resources.
  7. The Event Loop processes the simple requests, i.e., non-blocking operations, like  I/O Polling, and returns the responses to its corresponding clients.

5. How are packages managed in your Node.js project?

The Node package manager has the complete set of commands that manages the npm modules on a local system like installation, searching, un-installation, etc. The package. JSON file holds the whole metadata information for an npm module.

6. Explain the term I/O?

I/O stands for “Input/Output.”  Computers are based on the basic fundamental idea that every input results in an output. The ports on the outside of the computer are commonly called the “I/O ports” because they the ones that connect input and output devices to the computer.

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7. Is Node.js Single-threaded?

Yes! Node.js is single-threaded. It follows a Single-Threaded with Event Loop Model inspired by the JavaScript Event-based model with the JavaScript callback mechanism. So, Node.js is a single-threaded same as that of JavaScript but not purely like the JavaScript code, which implies things are done asynchronously like network calls, files, DNS lookup, system tasks, etc.

8. Explain how Node.js is better than other frameworks?

  1. Node.js provides simplicity because of its non-blocking I/O and even-based model that results in short response time and concurrent processing, not like other frameworks where developers make use of thread management. 
  2. It runs on a chrome v8 engine written in c++ and has high performance with constant improvement. 
  3. Since we use Javascript in both the frontend and backend, the development is much faster. 

9. Explain the term event-driven programming? 

event-driven programming

Event-driven programming is when the program is designed in such a way to respond to user engagement in different forms. It is called a programming paradigm where the flow of program execution is determined by the  “events.” Events can be any user interaction, like a click or keypress, in response to a prompt from the system.

10. Explain the concept of callback in Node.js?

The callback can be defined as an asynchronous equivalent for the function. A callback function is called on the completion of a given task. A node usually makes heavy use of callbacks. This makes Node.js highly scalable, as it processes a huge number of requests without waiting for any functions to return the results.

Node.js Interview Questions and Answers

11. Define the steps how “Control Flow” controls the functions calls?

Control flow function is a code that is implemented between the Asynchronous function calls. There are some steps given below to be followed while implementing it.

  1. The order of execution has to be controlled
  2. Collection of the required data is a must.
  3. The concurrency must be limited.
  4. When all the above processes are done, the next step of the program is requested.

12. Where is Node.js used?

  1. Streaming applications
  2. Microservices architecture
  3. Web development
  4. Network applications
  5. Distributed systems
  6. General-purpose applications
  7. Real-time chats
  8. Internet of Things

13. Differentiate between frontend and backend development?

Frontend DevelopmentBackend Development
The term front-end usually refers to the user interface.The term back-end” means the server, application, and database that are behind the scene to deliver information to users.
Languages used: HTML, CSS, JavaScript.Languages used: Node.js, c++, Python, PHP, Java.
Frameworks: AngularJS, React.js, SASS, Flutter, etc.Frameworks: Express, Django, Rails, Laravel, Spring.

14. Name some commonly used timing features of Node.js?

  1. Counts per second: It specifies the number of event loop iterations per second.
  2. count: It gives the total number of event loop iterations.
  3. startTime: It gives the timestamp at which the current iteration of the event loop began.
  4. duration: It gives the current duration of the current iteration of the event loop.

15. Name the two types of API functions in Node.js?

We have two types of API functions in Node.js:

  1. Asynchronous, non-blocking functions
  2. Synchronous blocking functions

 Node.js Interview Questions 

16. Define modules in Node.js?

A module in Node.js can be defined as a simple or complex functionality that is organized in single or multiple JavaScript files and can be reused throughout the Node.js application. Each of the modules in Node.js has its own context, so it cannot interfere with other modules.

17. Explain the advantages of using promises instead of callbacks?

The key advantages that the promises have over callback handlers:

  1. A better definition of control flow of asynchronous logic.
  2. Reduced coupling.
  3. Better error handling.
  4. Improved readability.

18. Define control flow function?

A control flow function in Node.js can be defined as a lightweight, generic piece of code that runs in between many asynchronous function calls and takes care of the required housekeeping to control the order of execution, limit concurrency,  collect data, etc.

19. Why do we prefer  Node.js over other backend technologies like Java and PHP?

  1. Node.js is very fast.
  2. Node Package Manager (NPM) has over 50,000 bundles that are available at the developer’s disposal.
  3. It is perfect for the real-time web, data-intensive applications because Node.js never waits for the API to return data.
  4. It provides better synchronization of code between client and server due to the same code base.
  5. It is easy for web developers to start using Node.js in their projects because it is a JavaScript library.

20. Define fork in Node.JS?

The fork method is a case of the spawn() to create the Node processes. This method returns an object which has a built-in communication channel in addition to all the methods in a normal ChildProcess instance.

Node.js Interview Questions 

21. Differentiate between Angular and Node.js?

AngularNode.js
It is an open-source framework for client-side applications.It is a cross-platform runtime system and environment for applications that are written in JavaScript.
You just have to add an AngularJS file like any other JavaScript file to use it in your applications.You have to install Node.js on the computer system.
It is written entirely in JavaScript. It is usually written in C, C++, and JavaScript languages.
It is suited for building single-page client-side web applications.We mainly use it to build fast and scalable server-side networking applications.

22. Write a code to create a simple server in Node.js that returns “Test Sample”?

var http = require("http");
http.createServer(function (request, response) {
  response.writeHead(200, {'Content-Type': 'text/plain'});
  response.end('Test Sample\n');
}).listen(3000);

23. Will the node run on windows?

Yes – it does. You have to download the MSI installer from their website.

24. Name the database that is more popularly used with Node.js?

MongoDB is the most popular database used with Node.js. MongoDB is a NoSQL, document-oriented, cross-platform database that aims to provide high performance, easy scalability, and high availability.

25. Define REPL in Node.js?

The Node. js REPL (Read-Eval-Print-Loop) can be defined as an interactive shell that processes the Node. The shell reads the JavaScript code that the user enters. It then evaluates the result of interpreting the line of code, and prints the result to the user, and loops it until the user signals to quit.

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 Node.js Interview Questions and Answers

26. Is it possible to access the DOM in the node?

No, you cannot access DOM in node.

27. Can you name some of the most commonly used libraries in Node.js?

Some of the commonly used libraries are listed below:

  1. Express: It is a Node.js library that is available through the npm registry. It is a very flexible, minimalist, and opinionated web framework.
  2. Gulp: It is a Node.js toolkit that helps to automate painful tasks and enhance the development workflow. One can install Gulp using the npm install command:
$npm install gulp
  1. Async: It is a utility module that allows us to work with asynchronous JavaScript and install NodeJS through npm async directly in the browser.
  2. Moment: It is a lightweight JavaScript date library used for manipulating, formatting, and parsing the dates.
  3. Lodash: It is a JavaScript utility library used to ease the programming tasks exported as the NodeJS modules.
  4. Cheerio: It is a fast and lean implementation of web scraping in JavaScript that is designed especially for the server.
  5. Nodemailer: It is a module for NodeJS applications that allows us to send emails from the NodeJS.

28. Name the two arguments that async.queue takes as input?

  1. Task Function
  2. Concurrency Value

29. Using the event loop, name the tasks that should be done asynchronously?

  1. I/O operations
  2. Heavy computation
  3. Anything requiring blocking

30. List the cons of Node.js?

Some of the disadvantages of Node.js are:

  1. It reduces the performance when handling Heavy Computing Tasks.
  2. It invites a lot of code changes due to its unstable API.
  3. Its  Asynchronous Programming Model makes it difficult to maintain the code.
  4. The lack of Library Support can Endanger your Code.

 Node.js Interview Questions 

31. What are the uses of the module.exports?

Module exports in Node.js are the instruction that tells the Node.js which bits of code like functions, objects, strings, etc. to “export” from the given file so that other files are allowed to access the exported.

32. Why is node.js becoming popular with JAVA programmers?

Node.js is becoming popular with JAVA programmers because it is a loop-based server for JavaScript. It gives users the ability to write JavaScript on the server, which in turn has access to things like HTTP  file I/O, stack, TCP, and databases.

33. Write the command used to import external libraries?

The command used to import external libraries is “require.”

Example: “var http=require (“HTTP”).”  

34. Name the tools used to assure consistent code style?

ESLint is used with any IDE, which ensures a consistent coding style and further helps in maintaining the codebase.

35. Define event loop in Node.js?

The event loop allows the  Node.js to perform non-blocking I/O operations. To process and handle the external events and to convert them into callback invocations, we make use of the event loop. So that at I/O calls, Node.js switches from one request to another.

 Node.js Interview Questions and Answers

36. Defne EventEmitter in Node.js?

The EventEmitter in Node.js is a module that facilitates the communication or interaction between the objects in Node. EventEmitter will be at the core of Node asynchronous event-driven architecture. Many of the Node’s built-in modules are inherited from EventEmitter that includes prominent frameworks like Express.js.

37. Explain the concept of callback hell?

Callback hell is a process that burdens a JavaScript developer when he tries to execute multiple asynchronous operations one after the other. Some people call it a pyramid of doom.

38. Name the steps by which you can async in Node.js?

  1. First-class functions
  2. Function composition
  3. Callback Counters
  4. Event loops

39. Define the package.json file?

All npm packages usually contain a file in the project root, known as a package. JSON – This file holds different metadata that is relevant to the project. This file gives the information to npm that allows to identify the project and handle the project’s dependencies.

40. Can you differentiate between process.nextTick() and setImmediate()?

process.nextTick()setImmediate()
It is processed after every phase of the event loop.It is only processed on the check handler phase of an event loop.
It fires immediately on the same phase.It fires on the following iteration or ‘tick’ of the event loop.

Node.js Interview Questions 

41. Explain how Node.js overcomes the problem of blocking the I/O operations?

Node.js solves the problem by placing the event-based model at its core, using an event loop instead of using threads.

42. What is the use of the URL module in Node.js?

The Node.js URL Module performs the operations with address URLs. Here, the web address is split into manageable parts. A URL string can carry information that includes the protocol like HTTPS, query string values, the hostname, etc.

43. Name the security implementations within Node.js?

The security implementations in Node.js are given below:

  1. Authentications
  2. Error Handling

44. Differentiate between Node.js vs. Ajax?

Node.jsAjax
It is a Server-Side JavaScript that is used for developing server software.Ajax is a client-side technology used for updating the contents of the given page without refreshing it.
Node is a full development environment that allows you to do things; Node.js cannot communicate with databases.It is just a technique to get data/scripts from an external file.
It is a server-side technology.It is a client-side technology.

45. Define Express.js package?

Express.js can be defined as a Node.js web application server framework, which is designed for building single-page, hybrid, and multi-page web applications. It is the standard server framework for Node.js. 

Node.js Interview Questions 

46. Define node.js streams?

Streams are the fundamental concepts that power Node.js applications. They are the data-handling methods used to read or write the input into output sequentially. Streams handle reading or writing files, network communications, or any kind of information exchange in an efficient way.

47. Name the types of streams in Node.js?

There are four types of stream, namely,

  1. Writable Stream: streams to which data can be written.
  2. Readable Stream: streams from which data can be read.
  3. Duplex Stream: streams that are Readable and Writeable. 
  4. Transform: Duplex streams that modify or transform the data as it is written and read.
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48. Explain the Challenges with Node.js maintenance?

  1. Extensive stack
  2. Technical debt
  3. Scalability challenges
  4. Poor documentation

49. How to create a simple Express.js application?

  1. The request object defines the HTTP request, and it has the properties for the request query string, body, HTTP headers, parameters, etc.
  2. The response object defines the HTTP response that an Express app sends when it receives the HTTP request.
Var express = require (‘express’)
Var app =express();
app.get(‘/’, function (req, res) {
res.send(‘Hello World”)
}};
app.listen(3000, function() {
console.log (‘ example app listening on port 30002’);

50. Explain the term non-blocking in Node.js?

Blocking relates to the operations that block further execution until that operation is finished. Non-blocking refers to the code that doesn’t block the execution. Or blocking is done when the execution of the additional JavaScript in the Node.js process has to wait until the non-JavaScript operation completes.

 Node.js Interview Questions 

51. Define asynchronous and non-blocking APIs in Node.js? 

asynchronous and non-blocking APIs

Asynchronous Input/Output is a type of input/output processing that permits the other processing to continue before finishing the transmission. 

Blocking relates to the operations that block further execution until that operation is finished. Non-blocking refers to the code that doesn’t block the execution. Or blocking is done when the execution of the additional JavaScript in the Node.js process has to wait until the non-JavaScript operation completes.

52. Define Node.js buffers?

The Buffer class in Node.js is used to handle raw binary data. Each buffer relates to some raw memory that is allocated outside V8. Buffers act like arrays of integers, but they are not resizable, and they have a whole bunch of methods for binary data.

53. Define callback function in Node.js?

The callback can be defined as an asynchronous equivalent for a function. All the APIs of Node are written to support callbacks.

 For example, a function that reads a file may start reading the file, and the control is returned to the execution environment so that the next instructions can be executed.

54. What is Middleware?

Middleware can be defined as a function that has access to the request object ( req ), a response object ( res ), and the next function, which is in the application’s request-response cycle. The next function in the Express router, when invoked, executes the middleware by succeeding the current middleware.

55. Differentiate between fork() and spawn() methods in Node.js?

fork()spawn()
It is an instance of spawn that runs a fresh instance of the V8 engine.It is a command designed to run system commands.
Multiple workers run on the single node code base for multiple tasks.It launches a new process with the available set of commands.

Node.js Interview Questions 

56. Define a Reactor Pattern in Node.js? 

Reactor Pattern is mainly used to avoid blocking of the Input/Output operations. When the I/O requests are generated, they should submit to a demultiplexer that handles concurrency in avoiding the blocking of the I/O mode, and it collects the requests in the form of the event and queues those events.

There are two components in this: 

Reactor: It dispatches the I/O event to appropriate handlers.

Handler: It actually works on those events.

57. Define Piping in Node.js?

Pipes in Node.js are used to connect multiple streams together. One of the examples is to pipe the read and write stream together to transfer the data from one file to the other. 

58. Why we have to separate the Express app and server?

The server is basically responsible for initializing the routes, middleware, and other application logic. The app has all the business logic, which will then be served by the routes that are initiated by the server. This ensures business logic is encapsulated and decoupled from application logic and makes the project more readable and maintainable.

59. Name some of the flags used in the read/write operations in files?

FlagDescription
rIt opens the file for reading. An exception will occur if the file does not exist.
r+It is used to open the file for reading and writing. An exception will occur if the file does not exist.
rsIt opens the file for reading in synchronous mode.
rs+It is used to open the file for reading and writing synchronously. 
wIt opens the file for writing. The file is created or truncated. 
aIt opens the file for appending. 

60. Why Google uses the V8 engine for Node.js?

The V8 Engine built by Google is an open-source that is written in C++. This engine is used inside Google Chrome. However, V8 is also used for Node.js.  In order to obtain the required speed, V8 translates the JavaScript code into a more efficient machine code instead of using the interpreter.

Node.js Interview Questions 

61. Define Test pyramid in Node.js? 

test pyramid

A test pyramid is defined as a metaphor that helps in the grouping of software tests in a bunch of different granularities. 

For example, unit testing, component testing, integration testing, system testing, end-to-end testing, UI testing

62. Define the exit codes of Node.js?

Exit codes give an idea of how a process got terminated or the reason behind termination. 

A few of them are:

  1. Uncaught fatal exception – (code – 1) – It specifies an exception that is not handled.
  2. Unused – (code – 2) – This is reserved by the bash.
  3. Fatal Error – (code – 5) – There is an error in V8 with stderr output of the description
  4. Internal Exception handler Run-time failure – (code – 7) – There is an exception when bootstrapping function was invoked.
  5. Internal JavaScript Evaluation Failure – (code – 4) – There was an exception when the bootstrapping process failed to return the function value when evaluated.

63. Name the different types of HTTP requests?

HTTP mainly defines a set of request methods that are used to perform desired actions. The request methods include:

  1. GET:  It is used to retrieve the data.
  2. POST: It is used to make a change in the state or reactions on a server.
  3. HEAD: It is similar to that of the GET method, but it asks for responses without a response body.
  4. DELETE: We mainly use it to delete the predetermined resource.

64. What is a stub in Node.js?

Stubs are wrapped into existing functions. When a stub is wrapped into the existing function, the original function doesn’t get called. Stubs are the functions or the programs that can affect the behavior of components or modules. 

65. What is NODE_ENV?

NODE_ENV is specifically used to state whether a specific environment is a production environment or a development environment. 

66. What is a Thread pool?

Thread pool

A thread pool can be defined as a set of worker threads that can efficiently execute the asynchronous callbacks on behalf of the application. The thread pool reduces the number of application threads and provides management of the worker threads.

67. What are Clusters?

A cluster can be defined as a pool of similar workers running under the parent Node process. Workers are spawned using the method fork() of the child_processes module. Meaning workers can share server handles and use the IPC to communicate with the parent Node process.

68. What is WASI?

Web assembly provides the implementation of the Web Assembly System Interface specification through WASI API in node.js that is implemented using WASI class.

69. How to connect a MongoDB database to Node.js?

To create a database in MongoDB, follows the given steps:

  1. Start by creating a MongoClient object.
  2. Next, specify the connection URL with the correct IP address and name of the database you want to create.

70. Explain how ‘Child Threads’ are handled in Node.js?

As we already know that javascript is a single-threaded application, so there is no concept of child threads in JS. When the asynchronous code is processed, that function is passed to the browser, and then the data is sent back to the JS when the event is ready to be processed further.

Since Node.js is a single thread process, it doesn’t expose the child threads and thread management methods to developers Node.js will spawn child threads for few tasks like asynchronous I/O, but they run behind the scenes and don’t execute any application JavaScript code or block the main event loop.

Good luck with your Node.js Interview, and we hope our Node.js Interview Questions and Answers were of some help to you. You can also check our Angular Interview Questions and MongoDB Interview Questions which might be of some help to you.

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