Interview Questions.

Node js Interview Questions


Node js Interview Questions

Node.Js was first of all advanced via Ryan Dahl and saw its first launch in May 2009. It is a JS environment used to execute JavaScript code outside the browser. Based on Chrome’s V8 engine, it represents the JavaScript everywhere and anywhere programming paradigm, unifying the web app improvement to a unmarried language as opposed to specific languages for server and customer-side scripting.

Many corporate including LinkedIn, IBM, GoDaddy, Groupon, Netflix, and Paypal use Node.Js. Its growing reputation has sparked a call for for Node.Js developers.

Node JS Interview Questions and Answers

If you desire to make a profession in Node.Js, below are the top Node js interview questions and solutions so that it will make you interview-ready.

Question: Explain the basics of Node.Js.

Answer: In its elemental feel, Node.Js is a JS runtime built using Chrome’s V8 JavaScript engine as a platform. Node.Js has gained reputation as it is light-weight and efficient, majorly because of its occasion-pushed and non-blockading I/O version. Built with overall performance as its primary consciousness, Node.Js is chargeable for processing the JavaScript code into the native system code, that could then be utilized by your computer to execute the approaches. Even even though it's far based on the V8 engine, that is utilized in Google Chrome and different chromium-primarily based browsers (Vivaldi, Brave and Opera), it does not run within the browser itself. During development, various functions including report device API, HTTP library and OS application strategies had been brought to the engine, in order that Node.Js can be done as a application on a computer.

Question: How are ‘Child Threads’ dealt with in Node.Js?

Answer: In its center experience, Node.Js is a unmarried thread process. Also, it does no longer reveal any infant threads and the modes of thread management to the developer. However, child threads can be generated in Node.Js in an expansion of approaches, one in all them being asynchronous I/O. Although the child threads spawned via those strategies run within the backdrop, they don’t block the main code or execute any application code. But if you require threading assist in an utility powered by using Node.Js, a couple of equipment are to be had for utilization.

Question: State some variations between Angular JS and Node.Js.

Answer: Below are some variations between Angular JS and Node.Js

Angular JS Node.js
Angular JS is written in TypeScript Node.js is written in a variety of languages, such as C, C++, and JavaScript
It is ideal while creating highly interactive web pages It is suited for small-scale projects and applications
It is an open-source framework for web application development It is a run-time environment based on multiple platforms
Used to create single-page applications for client-side Use to create server-side networking applications
Helps in splitting an application into model-view-controller (MVC) components Helps in generating queries for databases
Appropriate for the development of real-time applications It is appropriate in situations when something faster and highly scalable is required
Angular itself is a web application framework Node.js has many frameworks, including Express.js, Partial.js and more

Question: State the number one uses of Node.Js.


Complex unmarried-page programs: Node.Js is good for creating single-page applications which are complex in nature, consisting of on line drawing equipment, mail answers, and social networking. These styles of programs are limited to at least one-page and the UX is similar to that of a computing device software. Node.Js may be used here because of its asynchronous facts drift happening at the backend.

Real-Time Applications (RTA): We use a hefty wide variety of Real-Time applications in our everyday lifestyles. For instance, Google Docs, Slack, Skype, WhatsApp and lots of greater. Node.Js’ event API, WebSockets, and asynchronous statistics glide can make certain a wonderful server operation, with a purpose to update the statistics immediately.

Chat Rooms: This may be clubbed underneath RTA, however due to the fact that immediately messaging and chatting has emerged as one of the pinnacle real-time application fashions, it wishes a special awareness. If your product is in this realm, you're looking at requirements inclusive of light-weight, high site visitors ability and substantial information go with the flow. All those necessities can be fulfilled the usage of Node.Js and a few JavaScript framework on the backend. The aforementioned web sockets are available in accessible in receiving and sending messages in a chat room surroundings.

Browser-Based Games: The above-mentioned chat rooms can also be incorporated into browser-primarily based games, where Node.Js is a super desire. Combining the Node.Js technology with HTML5 or even JS gear will assist you create actual-time browser-based totally video games.

Data Streaming Applications: Another form of utility wherein Node.Js is best is records streaming applications. The key selling point of those packages is that they can method facts within the unloading phase. Through this, whilst a few elements can be downloaded prematurely to hold the connection and might down load the other parts if and whilst vital. In this context, Node.Js streaming packages address both audio and video facts.

Representational State Transfer (REST) Application Programming Interfaces (APIs): APIs based on REST keep a key position inside the construction of present day business software architecture due to the wide usage of the HyperText Transfer Protocol (HTTP). The Express.Js framework of the Node.Js environment can help in building rapid and mild REST APIs.

Server-Side Web Applications: While Node.Js and its frameworks can assist in developing server-aspect internet programs, it have to be cited that CPU-heavy operations should now not be predicted.

Command Line Tools: Node.Js’ expansive surroundings is an advantage with regards to constructing a command line tool, and there are a variety of tutorials to be had on line which will let you construct your very own CLT.

Question: What is Event-Driven programming?

Answer: Event-Driven programming technique profoundly uses occasions to trigger diverse capabilities. In this situation, an occasion can be something, which includes the urgent of a key or clicking of a mouse button. Whenever an event takes place, a name-lower back characteristic already registered with the element is achieved, following the ‘submit-subscribe’ sample. Due to this programming approach, Node.Js is quicker than different comparable technologies.

Question: In the context of Node.Js, what's REPL?

Answer: In the context of Node.Js, REPL is Read, Eval, Print and Loop. REPL is a computer environment (just like a Windows console or Linux shell) where any command that is entered is met with a machine answered output. The REPL surroundings is bundled with Node.Js by using default, and it plays the following obligations:

Read: Reads the inputs from the person and converts it into JavaScript records-structure, sooner or later storing it in memory

Eval: It gets the records structure and evaluates it

Print: It prints the very last output

Loop: It loops the provided command till CTRL + C is pressed two instances

Question: What is a check pyramid in Node.Js?

Answer: In Node.Js, a take a look at pyramid is a discern which explains the percentage of unit exams, integrations checks, and give up-to-cease tests are required for the fruitful improvement of a undertaking. The additives of a check pyramid are given underneath:

Unit Tests: They check the man or woman units of code in isolation. They are speedy and you may perform quite a few those assessments

Integrations Tests: They check the integration among distinctive gadgets.

End-to-End (E2E) Tests: They test the gadget as a whole, proper from the User Interface to the information shop, and again.

Question: What is libuv?

Answer: Libuv, a help library of Node.Js, is used for asynchronous Input/output. While it become to begin with developed only for Node.Js, it now witnesses exercise with different structures such as Luvit, Julia, Pyuv and extra. Some of the functions of Libuv are:

File System Events

Child Processes

Full-featured event loop backed

Asynchronous TCP & UDP sockets

Question: Is Node.Js the excellent platform for CPU-heavy programs?

Answer: Even though Node.Js can help in creating server-aspect applications, CPU-incentive applications are not the sturdy in shape of Node.Js. The CPU-heavy operations pave the manner for the blockage of incoming requests and push the thread into essential conditions.

Question: What is the reason of the Express JS Package?

Answer: Built on top of Node.Js, ExpressJS is a JS framework used to manage the float of data among the routes and server in server-side apps. Being light-weight, flexible and full of a selection of applicable capabilities, it's far apt for cellular and net application development.

Question: What are the main variations among Node.Js vs Javascript?


Node.js JavaScript
Cross-platform open source JS runtime engine.  A high-level scripting language based on the concept of OOPS.
Code can be run outside the browser.  Code can run only in the browser.
Used on server-side. Used on client-side.
No capabilities to add HTML tags. HTML tags can be added. 
Can be run only on Google Chrome's V8 engine. Can be run on any browser.
Written in C++ and JavaScript. An upgraded version of ECMA script written in C++.

Question: What are the major advantages of Node.Js?

Answer: Some fundamental benefits of Node.Js are:

smooth to research and huge community help.

Easy scalability and high performance.

Pretty extensible with extended aid.

Full-stack JavaScript.

Caching mechanism allows net pages to load quicker.

Non-blockading I/O structures.

Question: Explain the difference among Asynchronous and Non-blocking off?

Answer: Asynchronous or non-synchronous means that for a message despatched, we are able to no longer obtain a reaction right now; for that reason, there is no dependency or order of execution. The server stores information and an acknowledgement is received when the motion is done. This improves performance and performance.

Non-blocking operation, as the name suggests, does no longer stop or block any operations. The distinction is that non-blocking operation receives a reaction at once with whatever records is available. If information is not to be had, it returns an errors. It is normally used with I/O.

Question: Explain bundle.Json?

Answer: The npm applications contain a file package.Json inside the assignment root folder, which includes the metadata relevant to the challenge. It offers facts to the npm thru which npm identifies a undertaking and its dependencies. Apart from this, it carries other metadata like undertaking description, version, license statistics and configuration information. 

Question: Describe errors-first callback in Node.Js?

Answer: The error-first callback, additionally called as errorback gives the mistake and statistics. It takes a few arguments, the first one being the mistake object and others being the records. The errors-first callback sample has many benefits: for the reason that it is steady, leads to more adoption, if there may be no reference to the facts, there may be no need to technique it. If there is no blunders, the callback is referred to as with null because the first argument. 

Question: Explain the cause of module.Exports.

Answer: The cause is to offer commands to inform Node.Js approximately which a part of the code like items, capabilities, strings etc. Should be exported from a given record so that different documents can access it. Suppose we've got a module that looks as if:

    id: '.',
    exports: {},
    parent: null,
    filename: '/modtest.js',
    loaded: false,
    children: [],

Note that the exports belongings is empty, now if we observe code to this property, that will become the export of the module. If we require the module in some other record, with a view to be the export property fee:

module.exports.stringProperty = "Hello, welcome";
    id: '.',
    exports: { stringProperty: 'Hello, welcome' }

Question: What is the Reactor Pattern in Node.Js?

Answer: It is a idea of non-blocking I/O operations in Node.Js. Through this pattern, we get the handler (or callback characteristic) for every I/O operation. Each I/O request is submitted to a demultiplexer, that handles concurrency and queues the requests/events. Reactor sample includes assets, event notifier/demultiplexer, event loop, occasion queue, request handler.

Question: Explain LTS releases of Node.Js

Answer: LTS or Long-Term Support is implemented to launch lines which are supported and maintained by means of Node.Js project for an extended length. There are two forms of LTS: 

Active, which is actively maintained and upgraded, and 

protection line that is nearing its give up of the road and is maintained for a brief window of time.

Question: What is a URL module?

Answer: The URL module affords APIs to work with URLs:

a legacy API which is particular to Node.Js.

More recent API that implements WHATWG URL Standard used by internet browsers.

Some example strategies are URL.Port, URL.Password, URL.Host, url.ToString() under the URL magnificence. For the full documentation, take a look at the legit URL module web page.

Question: Explain the working mechanism of manipulate float feature?

Answer: Control go with the flow characteristic is the sequence in which statements or functions are achieved. Since I/O operations are non-blocking off in Node.Js, manage float can not be linear. Therefore, it registers a callback to the occasion loop and passes the control back to the node, in order that the next traces of code can run with out interruption. For example:

[code language="javascript"]
fs.readFile('/root/text.txt', func(err, data){
console.log("This is displayed first");

In this, the readFile operation will make an effort; however, the following console.Log isn't blocked. Once the operation completes, information may be displayed.

Question: What are the principle variations among spawn() and fork() strategies in Node.Js?


Spawn Fork
Designed to run system commands. A special instance of spawn() that runs a new instance of V8.
Does not execute any other code within the node process.  Can create multiple workers that run on the same Node codebase.
child_process.spawn(command[, args][, options]) creates a new process with the given command.  Special case of spawn() to create child processes using. child_process.fork(modulePath[, args][, options])
Creates a streaming interface (data buffering in binary format) between parent and child process. Creates a communication (messaging) channel between parent and child process.
More useful for continuous operations like data streaming (read/write), example, streaming images/files from the spawn process to the parent process. More useful for messaging, example, JSON or XML data messaging.

Question: What is the motive of ExpressJS bundle in Node.Js?

Answer: ExpressJS bundle or framework is constructed on top of Node.Js to fast-tune the improvement of unmarried-web page, multi-web page and hybrid server-primarily based programs. Express is said to be the backend part of the MEAN stack.

Question: Highlight the differences among method.NextTick() and setImmediate().


let execseq = function() {  
 setImmediate(() => console.log("immediate"));  
 process.nextTick(() => console.log("nextTick"));  
 console.log("event loop");

Question: Explain the distinction between Node.Js vs Ajax?

Answer: Ajax is a client-aspect technology and is used for updating web page content material with out refreshing the equal. Node.Js is a server-aspect JavaScript this is used to broaden server software program. Further, Node.Js is a full-fledged development environment, whereas Ajax is used just to attain records or run scripts.

Question: Give the reason why Express' app' and 'server' ought to be stored separate.

Answer: If we maintain the app and server functionalities separate, the code may be divided into more than one modules, thereby decreasing the dependency between modules. Each module will perform a single assignment. Also, due to the separation of good judgment, we can keep away from duplicate code.

Question: Explain the Difference among setImmediate() vs setTimeout().

Answer: While the word immediately is barely deceptive, the callback happens best after the I/O occasions callbacks, whilst we name setImmediate(). SetTimeout() is used to set a delay (in milliseconds) for execution of a one-time callback. If we execute, 

setImmediate(function() {
setTimeout(function() {
}, 0)

We will get the output as 'setTimeOut' and then 'setImmediate'.

Question: List Out and give an explanation for the popular modules of Node.Js?

Answer: The middle modules of Node.Js are:

http includes classes, methods and events for creating Node.js http server.
URL contains methods for URL resolution and parsing.
querystring deals with query string.
path contains methods for working with file paths.
fs consists of classes, methods, and events for handling file I/O.
util util module includes utility functions useful for developers.

Question: Add an instance of Streams in Node.Js?

Answer: Example of analyzing from flow:

var readStream = fs.createReadStream('data.txt');
readStream.on('data', function(chunk) {
   data += chunk;

Example of writing into move:

var writeStream = fs.createWriteStream('dataout.txt');

Question: What is crypto in Node.Js? How is it used?

Answer: The crypto module in Node.Js is used for cryptography, i.E. Consists of a hard and fast of wrappers for open SSL's hash, HMAC, signal, decipher, cipher and verify functions.

Here is an instance of the use of cipher for encryption:

const crypto = require('crypto');  
const cipher = crypto.createCipher('usrnm', 'pwdd');  
var encryptd = cipher.update('Welcome to hackr', 'utf8', 'hex');  
encryptd +='hex');  

Let’s use decipher to decrypt the above to look if we get the same textual content lower back:

const crypto = require('crypto');  
const decipher = crypto.createDecipher('usrnm', 'pwdd');  
var encryptd = '<enter the previous output-encrypted code here>';  
var decryptd = decipher.update(encryptd, 'hex', 'utf8');  
decryptd +='utf8');  

Question: Explain using the DNS module in Node.Js?

Answer: The DNS module is used for resolving a call. It is furnished through the running system and is used for the real DNS research too. With this module, it isn't required to memorize the IP addresses because the DNS servers convert domain/subdomain into IP addresses.

Question: Explain the safety mechanism of Node.Js?

Answer: Some mechanisms are:

Authorization codes: We can use authorization codes to secure Node.Js. That manner, any 0.33 birthday party that wants to get right of entry to Node.Js goes via the GET request of the resource company's network. 

Certified Modules: Certification modules are like filters that test the libraries of Node.Js to discover if any 1/3-party code is present or not. Any hacking can be detected using certifications. 

Curated Screening sign up: This is a exceptional manipulate machine wherein all of the programs (code and software program) are checked to make certain their safety. This experiment helps to dispose of unverified or unreliable libraries stepping into your utility.

Regular updates: Downloading the newest version of Node.Js will save you capability hackers and assaults. 

Question: Explain numerous styles of API capabilities in Node.Js.

Answer: The two forms of API functions in Node.Js are:

Asynchronous/Non-blocking off: These requests do now not look forward to the server to reply. They continue to procedure the subsequent request, and once the reaction is received, they get hold of the identical.

Synchronous/Blocking: These are requests that block every other requests. Once the request is finished, simplest then the following one is taken up.

Question: What are LTS versions of Node.Js?

Answer: Long Term Support or LTS version/releases of Node.Js are the releases which get hold of all the critical fixes, performance step usaand security updates. These variations obtain guide for at least 1.Five years and have a focal point on protection and stability of the application.

Question: Explain the running of assert in Node.Js

Answer: Assert is used to put in writing checks in Node.Js. The feedback is supplied best if any of the check cases which are jogging fails. To test invariants, the module offers you a set of assertion tests. It is used internally by using Node.Js, however if you use require (‘assert’) code, you'll be capable of use it in other applications as properly.

Question: What is callback hell?

Answer: In Node.Js, callback hell is likewise known as the Pyramid of Doom. Caused by way of intensively nested, unreadable and unmanageable callbacks, making the code harder to read and debug. It is induced due to fallacious execution of the asynchronous logic.

Question: What is stub in Node.Js?

Answer: Stubs are programs or features used to stimulate element behavior. Stubs offer the answers to the capabilities in the course of test instances.

Question: What is Event Loop?

Answer: All the asynchronous callbacks are dealt with by using an occasion loop in Node.Js. It is the foundation of the non-blockading enter/output in Node.Js, making it one of the most important functions of the environment. Due to the nature of Node.Js being occasion-pushed, a listener may be attached to an occasion for the callback to be executed by using the former when the occasion takes place. Node.Js executes the occasion loop after which moves directly to the rest of the code, without having to watch for the output. Once the whole operation culminates, it receives the output and the callback function is achieved. Once it receives the response, the features are achieved one by one.

Question: What is flow in Node.Js? What are its kinds?

Answer: In Node.Js, streams are the collection of facts similar to strings and arrays. Moreover, streams are gadgets via which you may examine source records or write vacation spot statistics constantly. These streams are especially useful for reading and processing big quantities of information. There are four varieties of streams in Node.Js, which can be:

Readable: Used to examine big quantity of records from supply

Writeable: Used to write statistics to destination

Duplex: Used for each read and write

Transform: A duplex movement used for facts modification

Question: List and explain the timing functions of Node.Js.

Answer: A timer module containing a couple of functions for the execution of the code after a selected term is supplied by using Node.Js. Some of the capabilities provided in this module are:

technique.NextTick: This characteristic schedules a callback function which is required to be invoked in the next generation of the event loop

setTimeout/clearTimeout: This function schedules code execution after the assigned amount of time (in milliseconds)

setImmediate/clearImmediate: This capabilities executes code at the conclusion of the prevailing occasion loop cycle

setInterval/clearInterval: This feature is used to execute a block of code a number of instances

Question: Highlight the differences among manner.NextTick() and setImmediate().

Answer: Both procedure.NextTick() and setImmediate() are features of the Timers module, however the distinction lies in their execution.

The technique.NextTick() feature waits for the execution of motion until the subsequent bypass round inside the occasion loop or whilst the occasion loop culminates, then best the callback characteristic is invoked.

The setImmediate() characteristic is used for callback method execution on the next cycle of the occasion loop, which returns it to the event loop for the execution of the enter/output operations.

Question: Explain readFile and createReadStream in Node.Js.

Answer: Both readFile and createReadStream are approaches to study and execute files furnished with the aid of the Node.Js.

The readFile system is fully buffered which returns reaction(s) most effective if the entire file is entered into the buffer and may be read. This technique is highly memory intensive and might grow to be gradual in case the document size is huge.

The createReadStream technique is partially buffered, treating the complete manner as a chain of occasions. In this method, the whole documents are cut up into chunks that are processed after which despatched as a response individually in succession. Unlike readFile, createReadStream is effective in terms of reading and processing massive files.

Question: Does Node.Js offer a Debugger?

Answer: A built-in TCP protocol and the debugging client is provided through Node.Js. If you want to debug your file, you could use the following argument earlier than the name of your JS report that you wish to debug.

node debug [script.js | -e “script” | :]

Answer: Exit codes in Node.Js are a particular organization of codes that end off strategies, that could include worldwide objects as well. Some of the go out codes in Node.Js are:

Internal JavaScript Evaluation Failure

Fatal Error

Internal Exception handler Run-time failure


Uncaught deadly exception

Question: Why is NODE_ENV used?

Answer: When any Node.Js task is inside the stage of production, Node.Js promotes the principle to use NODE_ENV variable to flag it. When the NODE-ENV is about to manufacturing, your software will perform at a speed 2 to three times quicker than ordinary. The variable additionally improves judgment during the development segment of initiatives.

Question: What is Event Emitter in Node.Js?

Answer: Node.Js has an EventEmitter class which holds all the items that may emit activities. These gadgets preserve a feature known as eventEmitter.On() using which multiple features can be attached to the occasion emitted by using the object. Whenever an item from the EventEmitter magnificence throws an occasion, all of the connected features to the vent are known as upon synchronously.

Question: What is Punycode?

Answer: Punycode can be defined as an encoding syntax in Node.Js that's beneficial for changing the Unicode string of characters into ASCII. This is executed as the hostnames can simplest realize ASCII codes and now not Unicode. While it was bundled up within the default bundle in recent variations, you may use it within the preceding version the use of the following code:

punycode = require(‘punycode’);

Question: Explain the concept of JIT and spotlight its relation with Node.Js.

Answer: A JIT or Just-in-time compiler sends bytecode (which include interpretable commands) to the processor through changing it into instruction. Once you are completed with the writing a part of a application, the source language statements are compiled into bytecode with the aid of the compiler, instead of the code that contains the records that's similar to the destination hardware platform processor.

Node.Js employs JIT compilation which improves the speed of code execution to a extraordinary extent. It takes the source code and converts it into machine code in runtime. Through this, features which can be known as regularly are compiled to system code, growing the general velocity of code execution.

Question: Why is the buffer elegance utilized in Node.Js?

Answer: In Node.Js, the buffer magnificence stores the uncooked information, in a manner similar to that of an array of integers. However, it communicates to a uncooked memory unload, allotted out of doors the V8 heap. The Buffer class is a global magnificence and may be accessed in an software without having to import the buffer module. It is majorly used as pure JavaScript code is not attuned with binary records.

Question: What is the difference among fork () and spawn () techniques in Node.Js?

Answer: In Node.Js, spawn () launches a new method with the to be had set of instructions. This doesn’t generate a new V8 example handiest a single copy of the node module is energetic at the processor. This approach may be used when your child technique returns a big quantity of data to the node.

On the opposite hand, fork () is a particular case of spawn () which generates a brand new V8 engines instance. Through this technique, multiple employees run on a single node code base for a couple of duties.

Question: State the steps to write down an Express JS software.

Answer: To set up an ExpressJs application, you need to comply with the following steps:

Create a folder with the undertaking name

Create a document named bundle.Json inside the folder

Run the ‘npm set up’ command on the command prompt to install the libraries present within the package file

Create a report named server.Js

Create the ‘router’ file within the package along with a folder named as index.Js

The application is created inside the package deal containing the index.Html file

With this, we come to an end of the pinnacle Node.Js interview questions. Do you think we neglected an crucial query or have any doubts that need to be cleared? Let us understand inside the feedback underneath. You also can take a look at our great Node.Js tutorials, curated with the aid of network participants.