Node.js Interview Questions and Answers -

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

Node.js is an open-source, cross-platform JavaScript runtime environment and library to run web applications outside the client’s browser. It is used to create server-side web applications.

Node.js is perfect for data-intensive applications as it uses an asynchronous, event-driven model. You can use I/O intensive web applications like video streaming sites. You can also use it for developing: Real-time web applications, Network applications, General-purpose

2. Why is Node.js Single-threaded?

Node.js is single-threaded for async processing. By doing async processing on a single-thread under typical web loads, more performance and scalability can be achieved instead of the typical thread-based implementation.

3. Why use Node.js?

Far far away, behind the word mountains, far from the countries Vokalia and Consonantia, there live the blind texts. Separated they live in Bookmarksgrove right at the coast

4. Node.js makes building scalable network programs easy. Some of its advantages include:

a) It is generally fast

b) It rarely blocks

c) It offers a unified programming language and data type

d) Everything is asynchronous

e) It yields great concurrency

5. How does Node.js work?

1) Clients send requests to the webserver to interact with the web application. Requests can be non-blocking or blocking:

2) Querying for data

3) Deleting data

4) Updating the data

5) Node.js retrieves the incoming requests and adds those to the Event Queue

6) The requests are then passed one-by-one through the Event Loop. It checks if the requests are simple enough not to require any external resources

7) The Event Loop processes simple requests (non-blocking operations), such as I/O Polling, and returns the responses to the corresponding clients

A single thread from the Thread Pool is assigned to a single complex request. This thread is responsible for completing a particular blocking request by accessing external resources, such as computation, database, file system, etc.

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

1) The control flow of asynchronous logic is more specified and structured.

2) The coupling is low.

3) We've built-in error handling.

4) Improved readability.

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

The Multi-Threaded Request/Response Stateless Model is not followed by the Node JS Platform, and it adheres to the Single-Threaded Event Loop Model. The Node JS Processing paradigm is heavily influenced by the JavaScript Event-based model and the JavaScript callback system. As a result, Node.js can easily manage more concurrent client requests. The event loop is the processing model's beating heart in Node.js.

8. Explain callback in Node.js.

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

9. How is Node.js most frequently used?

Node.js is widely used in the following applications:

1) Real-time chats

2) Internet of Things

3) Complex SPAs (Single-Page Applications)

4) Real-time collaboration tools

5) Streaming applications

6) Microservices architecture

10. 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

Every transfer is an output from one medium and an input into another. The medium can be a physical device, network, or files within a system

11. Explain the difference between frontend and backend development?

Front-end	Back-end
Frontend refers to the client-side of an application	Backend refers to the server-side of an application
It is the part of a web application that users can see and interact with	It constitutes everything that happens behind the scenes
It typically includes everything that attributes to the visual aspects of a web application	It generally includes a web server that communicates with a database to serve requests
HTML, CSS, JavaScript, AngularJS, and ReactJS are some of the essentials of frontend development	Java, PHP, Python, and Node.js are some of the backend development technologies

12. What are the pros and cons of Node.js?

Node.js Pros	Node.js Cons
Fast processing and an event-based model	Not suitable for heavy computational tasks
Uses JavaScript, which is well-known amongst developers	Using callback is complex since you end up with several nested callbacks
Node Package Manager has over 50,000 packages that provide the functionality to an application	Dealing with relational databases is not a good option for Node.js
Best suited for streaming huge amounts of data and I/O intensive operations	Since Node.js is single-threaded, CPU intensive tasks are not its strong suit

13. What is the difference between Angular and Node.js?

Angular	Node.js
It is a frontend development framework	It is a server-side environment
It is written in TypeScript	It is written in C, C++ languages
Used for building single-page, client-side web applications	Used for building fast and scalable server-side networking applications
Splits a web application into MVC components	Generates database queries

14. What is NPM?

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

Node Package Manager provides two main functionalities:

1) Provides online repositories for node.js packages/modules, which are searchable on search.nodejs.org

2) Provides online repositories for node.js packages/modules, which are searchable on search.nodejs.org

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

Some of the reasons why Node.js is preferred include:

1) Node.js is very fast

2) Node Package Manager has over 50,000 bundles available at the developer’s disposal

3) Perfect for data-intensive, real-time web applications, as Node.js never waits for an API to return data

4) Better synchronization of code between server and client due to same code base

5) Easy for web developers to start using Node.js in their projects as it is a JavaScript library

16. Which database is more popularly used with Node.js?

MongoDB is the most common database used with Node.js. It is a NoSQL, cross-platform, document-oriented database that provides high performance, high availability, and easy scalability

17. What is the purpose of the module .Exports?

In Node.js, a module encapsulates all related codes into a single unit of code that can be parsed by moving all relevant functions into a single file. You may export a module with the module and export the function, which lets it be imported into another file with a needed keyword.

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

19. What is the command used to import external libraries?

The “require” command is used for importing external libraries. For example - “var http=require (“HTTP”).” This will load the HTTP library and the single exported object through the HTTP variable.

Now that we have covered some of the important beginner-level Node.js interview questions let us look at some of the intermediate-level Node.js interview questions.

20. What are the modules in Node.js?

Modules are like JavaScript libraries that can be used in a Node.js application to include a set of functions. To include a module in a Node.js application, use the require() function with the parentheses containing the module's name.

Node.js has many modules to provide the basic functionality needed for a web application. Some of them include:

Core Modules	Description
HTTP	Includes classes, methods, and events to create a Node.js HTTP server
util	Includes utility functions useful for developers
fs	Includes events, classes, and methods to deal with file I/O operations
url	Includes methods to work with query string
query string	Includes methods to work with query string
stream	Includes methods to handle streaming data
zlib	Includes methods to compress or decompress files

Node.js Interview Questions and Answers For Intermediate Level

21. What does event-driven programming mean?

An event-driven programming approach uses events to trigger various functions. An event can be anything, such as typing a key or clicking a mouse button. A call-back function is already registered with the element executes whenever an event is triggered.

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

The two types of API functions in Node.js are:

1) Asynchronous, non-blocking functions

2) Synchronous, blocking functions

23.What is an EventEmitter in Node.js?

EventEmitter is a class that holds all the objects that can emit events

Whenever an object from the EventEmitter class throws an event, all attached functions are called upon synchronously

24. Differentiate between process.nextTick() and setImmediate()?

The distinction between method and product. This is accomplished through the use of nextTick() and setImmediate(). next Tick() postpones the execution of action until the next pass around the event loop, or it simply calls the callback function once the event loop's current execution is complete, whereas setImmediate() executes a callback on the next cycle of the event loop and returns control to the event loop for any I/O operations.

25. What is an Event Loop in Node.js?

Event loops handle asynchronous callbacks in Node.js. It is the foundation of the non-blocking input/output in Node.js, making it one of the most important environmental features.

26. What is the Express.js package?

Express is a flexible Node.js web application framework that provides a wide set of features to develop both web and mobile applications

27. What are streams in Node.js?

Streams are objects that enable you to read data or write data continuously.

Readable

Used for reading operations<

Writable

Used for write operations

Duplex

Can be used for both reading and write operations

Transform

A type of duplex stream where the output is computed based on input

28. What is the package.json file?

The package.json file is the heart of a Node.js system. This file holds the metadata for a particular project. The package.json file is found in the root directory of any Node application or module

This is what a package.json file looks like immediately after creating a Node.js project using the command: npm init

You can edit the parameters when you create a Node.js project.

29. How would you use a URL module in Node.js?

The URL module in Node.js provides various utilities for URL resolution and parsing. It is a built-in module that helps split up the web address into a readable format.

var url = require('url');

var adrs = "http://localhost:8080/default.hrm?year=2020&month=match';"

var que = url.parse(adrs, true);

console.log(que.host);//returns 'localhost:8080'

console.log(que,pathname); //returns '/default.htm'

console.log(que.search); //returns '?year=2020 and month=march'

var quedata = que.query; //returns an object: { year: 2020,month:'march'}

console.log(quedata.month); //returns 'march'

30. How do you create a simple Express.js application?

The request object represents the HTTP request and has properties for the request query string, parameters, body, HTTP headers, and so on

The response object represents the HTTP response that an Express app sends when it receives an HTTP request

var express = require( 'express' );

var app = express();

app.get('/' ,function(req,res){

res.send('hello word');

})

var server = app.listen(8081,function(){

var host = server.address().address

var port = server.address().port

console.log("example app listing at http://%s:%s" ,host,port)

})

31. How do we implement async in Node.js?

As shown below, the async code asks the JavaScript engine running the code to wait for the request.get() function to complete before moving on to the next line for execution.

async function fun1(req,res){

let response = await request.get('http://localhost:3000');

if(response.err){ console.log('error');}

else { console.log('fetched response');

}

32. How do you create a simple server in Node.js that returns Hello World?

1) Import the HTTP module

2) Use createServer function with a callback function using request and response as parameters.

3) Type “hello world."

4) Set the server to listen to port 8080 and assign an IP address

var http = require('http);

http.createserver(function(req,res){

res.writehead(200,{'content-type':'text/plain'});

res.end('hello world\n');

}).listen(8080,'727.0.01');

33.Explain asynchronous and non-blocking APIs in Node.js.

1) All Node.js library APIs are asynchronous, which means they are also non-blocking

2) A Node.js-based server never waits for an API to return data. Instead, it moves to the next API after calling it, and a notification mechanism from a Node.js event responds to the server for the previous API call

34. What is a callback function in Node.js?

A callback is a function called after a given task. This prevents any blocking and enables other code to run in the meantime.

Node.js Interview Questions and Answers For Experienced Professionals

This section will provide you with the Advanced Node.js interview questions which will primarily help experienced professionals.

35. What is the control flow function?

The control flow function is a piece of code that runs in between several asynchronous function calls.

36. What is REPL in Node.js?

REPL stands for Read Eval Print Loop, and it represents a computer environment. It’s similar to a Windows console or Unix/Linux shell in which a command is entered. Then, the system responds with an output

REPL Perform the following desired tasks:

Read: read users input, parses the input into JavaScript data structure and store memory

Eval: Takes and evaluate the data structure

Print: Print the result

Loop: Loops the above command untill user presses ctrl-c twice

37. How does control flow manage the function calls?

The Control flow does the following jobs:

1) Control the order of execution

2) Collect Data

3) Limit Concurrency

4) Call the next step program

38. What is piping in Node.js?

Piping is a mechanism used to connect the output of one stream to another stream. It is normally used to retrieve data from one stream and pass output to another stream

39. How to Change my Photo from Admin Dashboard?

Far far away, behind the word mountains, far from the countries Vokalia and Consonantia, there live the blind texts. Separated they live in Bookmarksgrove right at the coast

40. What is the difference between fork() and spawn() methods in Node.js?

Far far away, behind the word mountains, far from the countries Vokalia and Consonantia, there live the blind texts. Separated they live in Bookmarksgrove right at the coast

fork()	spawn()
fork() is a particular case of spawn() that generates a new instance of a V8 engine.	Spawn() launches a new process with the available set of commands.
Multiple workers run on a single node code base for multiple tasks.	This method doesn’t generate a new V8 instance, and only a single copy of the node module is active on the processor.

41. What is WASI, and why is it being introduced?

The WASI class implements the WASI system called API and extra convenience methods for interacting with WASI-based applications. Every WASI instance represents a unique sandbox environment. Each WASI instance must specify its command-line parameters, environment variables, and sandbox directory structure for security reasons.

42. What are the different types of HTTP requests?

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

GET:

Used to retrieve the data

POST

Generally used to make a change in state or reactions on the server

HEAD:

Similar to the GET method, but asks for the response without the response body

DELETE:

Used to delete the predetermined resource

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

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

1) Execute any code

2) Update or modify the request and the response objects

3) Finish the request-response cycle

4) Invoke the next middleware in the stack

44. What is fork in node JS?

A fork in general is used to spawn child processes. In node it is used to create a new instance of v8 engine to run multiple workers to execute the code.

45. For Node.js, why does Google use the V8 engine?

The V8 engine, developed by Google, is open-source and written in C++. Google Chrome makes use of this engine. V8, unlike the other engines, is also utilized for the popular Node.js runtime. V8 was initially intended to improve the speed of JavaScript execution within web browsers. Instead of employing an interpreter, V8 converts JavaScript code into more efficient machine code to increase performance. It turns JavaScript code into machine code during execution by utilizing a JIT (Just-In-Time) compiler, as do many current JavaScript engines such as SpiderMonkey or Rhino (Mozilla).

46. How would you connect a MongoDB database to Node.js?

To create a database in MongoDB:

1) Start by creating a MongoClient object

2) Specify a connection URL with the correct IP address and the name of the database you want to create

var mongoclient = required('mongodb').mongoclient;

var url = "mongodp://localhost:27017/mydp";

mongoclient.connect(url,function(err,dp){

if(err) throw err;

console.log("database created!");

db.close();

});

47. Describe Node.js exit codes.

Exit Codes are set of specific codes which are used for finishing specific process. given below are some of the exit used in node.js

1) Uncaught fatal exception

2) Unused

3) Fatal Error

4) Internal Exception handler Rub-time failure.

48. How do you open a file in Node.js?

fs.open(path, flags[,model], callback

49. What is a test pyramid in Node.js?

Essentially, the test pyramid describes that you should write unit tests, integration tests and end-to-end tests as well. You should have more integration tests than end-to-end tests, and even more unit tests. Let's take a look at how you can add unit tests for your applications!

50. What is the purpose of NODE_ENV?

NODE_ENV specifically is used (by convention) to state whether a particular environment is a production or a development environment. A common use-case is running additional debugging or logging code if running in a development environment.

Top 50 Node JS Interview Questions and Answers

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

2. Why is Node.js Single-threaded?

3. Why use Node.js?

4. Node.js makes building scalable network programs easy. Some of its advantages include:

5. How does Node.js work?

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

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

8. Explain callback in Node.js.

9. How is Node.js most frequently used?

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

11. Explain the difference between frontend and backend development?

12. What are the pros and cons of Node.js?

13. What is the difference between Angular and Node.js?

14. What is NPM?

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

16. Which database is more popularly used with Node.js?

17. What is the purpose of the module .Exports?

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

19. What is the command used to import external libraries?

20. What are the modules in Node.js?

Node.js Interview Questions and Answers For Intermediate Level

21. What does event-driven programming mean?

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

23.What is an EventEmitter in Node.js?

24. Differentiate between process.nextTick() and setImmediate()?

25. What is an Event Loop in Node.js?

26. What is the Express.js package?

27. What are streams in Node.js?

Readable

Writable

Duplex

Transform

28. What is the package.json file?

29. How would you use a URL module in Node.js?

30. How do you create a simple Express.js application?

31. How do we implement async in Node.js?

32. How do you create a simple server in Node.js that returns Hello World?

33.Explain asynchronous and non-blocking APIs in Node.js.

34. What is a callback function in Node.js?

Node.js Interview Questions and Answers For Experienced Professionals

35. What is the control flow function?

36. What is REPL in Node.js?

37. How does control flow manage the function calls?

38. What is piping in Node.js?

39. How to Change my Photo from Admin Dashboard?

40. What is the difference between fork() and spawn() methods in Node.js?

41. What is WASI, and why is it being introduced?

42. What are the different types of HTTP requests?

GET:

POST

HEAD:

DELETE:

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

44. What is fork in node JS?

45. For Node.js, why does Google use the V8 engine?

46. How would you connect a MongoDB database to Node.js?

47. Describe Node.js exit codes.

48. How do you open a file in Node.js?

49. What is a test pyramid in Node.js?

50. What is the purpose of NODE_ENV?

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