ExpressJS Interview Questions and Answers

ExpressJS is the most used and popular server-side scripting tool to create everything from an easy-grip line program to compound enterprise-level web applications with equal ease. This is the only reason why many organizations demand certified ExpressJS developers for providing the management of the entire server-side.

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ExpressJS Interview Questions and Answers

ExpressJS is the most used and popular server-side scripting tool to create everything from an easy-grip line program to compound enterprise-level web applications with equal ease. This is the only reason why many organizations demand certified ExpressJS developers for providing the management of the entire server-side. As a result, ExpressJS opens many career opportunities for candidates who wish to have a secure job in this field. 

Suppose you are an aspirant who is wishing to get the ExpressJS developer job. In that case, you should buckle up your preparation and start with the ExpressJS interview questions for getting the job post at the most famous organization quickly. This blog is framed to help the candidates with the top interview question on ExpressJS. Let’s start 

1- Describe the meaning of ExpressJS

A free, open-source, lightweight Node js-based application framework is the ExpressJS. ExpressJS was written in JavaScript by TJ Holowaychuk in 2010; it is formulated to develop web-related applications and APIs. 

2- Mention various features of ExpressJS 

The given points state the features of ExpressJS

● ExpressJS has middleware that responds to HTTP and restful requests. 

● With ExpressJS, the routing table can be defined for performing numerous HTTP operations. 

● ExpressJS renders HTML path thickness solely based upon arguments and templates. 

● ExpressJS is known for this thin layer and high performance. 

● ExpressJS has adequate support for RDBMS and NoSQL databases. 

● ExpressJS can organize web applications to MVC infrastructure. 

● ExpressJS manages all the tasks from routes for rendering views and performing HTTP requests. 

3- State the numerous ways to allow CORS in ExpressJS 

Cross-origin resource sharing is the device that allows the restriction of resources that will be requested from different domains. ExpressJS allows CORS as through. 

● CORS allows setting a single header through res.setheader() 

● For setting up multiple headers, res.header() OR res.set() will be used. 

● The module of express CORS. 

4- Define scaffolding of ExpressJS

Scaffolding is the process through which the creation of the skeleton of any application is possible. Scaffolding can be done in mainly two ways which are 

● Express application generator

● Yeoman

5- Explain routing and it’s working in ExpressJS 

Determining how the application responds to the client request in the particular endpoint with a URL and specific HTTP request method is said as the routing. The router has one or more handler functions through which the route executed is matched. The syntax of the route is app.METHOD(PATH, HANDLER)

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6- Define middleware in ExpressJS

The function is invoked through the express routing layer before the handler of the final request. Middleware in ExpressJS can perform numerous tasks like 

● The execution of any code. 

● It can make any changes in the request and response objects. 

● It can end the cycle of response requests. 

● Middleware can call the following middleware function in the stack. 

7- State the meaning of database integration in ExpressJS

Database integration can add the capability of connecting databases to the applications of ExpressJS in just a matter of loading in the NodeJS driver for the database in the application. ExpressJS supports numerous RDBMS and NoSQL database like 

● MongoDB


● Oracle

● PostgreSQL

● SQL server 

● SQLite

8- Mention the steps for setting ExpressJS application

The following steps given under can utilizes the setting up of the ExpressJS application 

● Require a folder with a constant name as the project name will be created. 

● Require the file name package.json within the folder. 

● The command npm. The install will be run in electronic communication.npm.install libraries of the packages. 

● The server.js file is created. 

● The file named router is made in the package, which consists of the folder name index.js

● The creation of the app in the package has an index.html file. 

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9- State the usage of the following in ExpressJS 

Next is responsible for passing management with the consecutive matching route. It operates to pass management to one of the route handlers. This argument needs to be omitted, which is beneficial whenever you get the series of handlers. 

10- Mention the features of the ExpressJS framework

Numerous core features of the ExpressJS are 

● ExpressJS frameworks allow setting the middleware for responding to HTTP requests. 

● It will define the routing table through which it can work as per the HTTP method and URL. 

● The express framework supports dynamic HTML pages. 

11- What is the method of getting variables in the ExpressJS of the GET method?

var express = 


var app=express();

app.get(‘/’, function(req, res){

   /*req have all the values**/




12- Give the syntax of removing debugging from express app

var io=

require(‘’).listen(app, {log:false});

io.set(‘log level’,1);

13- Give the syntax of the “next” parameter in ExpressJS 


function(req, res, next){


req and res represent the request and responding objects

Next passes control the next matching route. 

14- Which function arguments are available in ExpressJS route handlers?

The list of argument available under ExpressJS is 

● Req for requesting the objects. 

● Res for responding to the objects. 

● Next for employing to pass management to 1 of the route handlers. However, this argument is optional in the case of ExpressJS. 

15- What is the procedure of configuring properties of express application?

Under ExpressJS, mainly two methods are followed for configuring the properties as 

For env process 

● The name of the file env is created within the project. 

● The properties will be there in the .env file. 

● The properties can be employed under the server in ExpressJS. 

For require js process 

● The name of the file config.json.js created in the config folder within the project. 

● The properties are config which is to be present in the config.json file. 

● The access of accustomed will be the config.json file. 

16- Give the syntax for enabling debugging under express application

In Unix operating system, debugging can be availed through 

$ DEBUG=express:* node index.js

Whereas in Windows, the syntax will be 

set DEBUG=express:* & node index.js 

17- How to authenticate users?

It is one more authentication opinionated area that express doesn’t venture to. Authentication can be used for any authentication scheme. 

18- State the name of the template engine which ExpressJS support

The template engine, which has the signature, can easily be covered by ExpressJS like path, locals, and callback. 

19- State the reasons for using ExpressJS 

Various reasons for choosing ExpressJS are 

● ExpressJS framework is lighter in weight than any web application framework. 

● ExpressJS helps in organizing web applications to MVC architecture on the server-side. 

20- Describe the modules used in ExpressJS 

The framework of ExpressJS has no notion of the database. It is the concept that is left up to a third-party module. It can interface with any nearby data. Numerous modules used in ExpressJS are 


● util

● fs


● query string

● stream

● zlib

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21- Mention the uses of ExpressJS 

ExpressJS helps in developing scalable network programming efficiently. Many more reasons for using ExpressJS are 

● ExpressJS is fast. 

● ExpressJS doesn’t block easily. 

● ExpressJS offers a unified programming language and data type. 

● Under ExpressJS, everything is asynchronous. 

● ExpressJS has high concurrency. 

22- Is ExpressJS the fantastic platform for CPU-heavy applications?

ExpressJS is beneficial in creating server-side applications; CPU-enabled applications don’t suit ExpressJS. The CPU-heavy execution paves the way for blocking requests and pushing the threads to critical situations. 

23- Give the purpose of the ExpressJS package 

ExpressJS are the flexible NodeJS application framework that provides various features for developing web and mobile applications. It is used in managing the flow of information between routers and servers in server-side applications. It has numerous features because of its long-lasting features. Learn more at 3RI Technologies

24- State the advantages of ExpressJS 

The benefits of ExpressJS are given under 

● ExpressJS is very fast because it is built on a google V8 engine. 

● ExpressJS framework is asynchronous in which it never waits for API. 

● ExpressJS is highly scalable than other frameworks. 

● ExpressJS offers an open-source community to add excellent modules. 

● ExpressJS outputs the data in chunks. 

25- Define error first callback in ExpressJS

It is also known as the error back, which gives the error and data. ExpressJS takes numerous arguments out of which one is an error and others are objects. It offers many benefits as it is consistent, leads to adoption, and has no data reference. 

26- Define LTS release of ExpressJS 

LTS can also be said as Long-term support, which is applied to relate the lines supported and maintained through the ExpressJS project for the period of extension. Mainly two varieties of LTS are there 

● Active LTS, which are retained and updated. 

● The line of maintenance was nearing its end of the line and maintained for a shorter time. 

27- Give the difference between spawn() and fork() 

Spawn Fork 
It is designed for running the commands The instance of spawn runs the new instance of Google V8 
It doesn’t execute different code with the process It can create numerous workers which run on the same code. 
child_process.spawn creates the new process of the command The case of spawn is used in the creation of the child process. 
It creates the streaming interface between parent and child processIt creates the communication channel between parent and child process
It is more useful in operations like data streaming, file streaming of files, etc. It is used in JSON and data messaging. 

28- Give the example of streaming in ExpressJS 

var readStream =

fs.createReadStream( ‘data.txt’);


function(chunk) {

data += chunk;


29- Describe crypto 

It is the type of module used in ExpressJS that is further used in cryptography, including wrappers under open SSL hash, HMAC, sign, decipher cypher, and function verification. 

30- Give the usage of DNS in ExpressJS 

The module named DNS is used in resolving the name. DNS is provided through an operating system that is used for an actual DNS lookup. It is not required for memorizing the IP address as a DNS server that converts domain and subdomain. 

31- Describe the security mechanism of ExpressJS 

The security mechanism of ExpressJS is 

● Authorization of codes

● Certification of modules

● Screening curated register 

● Updates regulations

32- Define LTS version 

LTS version of ExpressJS is the type of release that receives critical fixes, performance step up, and security updates. In addition, LTS versions have the support of 1.5 years, focusing on the security and stability of the application. 

33- Give the assert working in ExpressJS 

The word assert is used in the writing of tests in ExpressJS. The feedback will only be given if the test cases fail. For testing invariants, the modules will provide the assertion tests. The assertion is used internally in ExpressJS, but this testing will let you use it in other web applications. 

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34- What is the use of NODE_ENV? 

Whenever the production stage in the ExpressJS project starts, it promotes using the principle NODE_ENV variable for flagging it. Thus, whenever the Node env is set for production, the application will be running 2 to 3 times faster. 

35- Define Punycode 

It can be defined as the encoding syntax of ExpressJS, which is helping in converting the Unicode string of characters into ASCII. Punycode is the hostnames that ASCII codes and Unicode can only comprehend. It was bundled up with the default package in the recent versions of the code. 

36- List various types of middleware 

Numerous types of middleware are 

● Application-level middleware 

● Router level middleware 

● Error handling middleware 

● Built-in middleware 

● Third-party middleware 

37- Define stub

These are the stub or functions which are used for stimulating the component behaviour. Also, stubs provide the answers to the function during the test cases. 

38- Describe the meaning of CLI 

The CLI is primarily known as the command-line interface. CLI is the utility or program where users type the command to perform the actions or run a script instead of clicking on the screen. Some CLI includes 

● Bash on Linux

● Terminal of MAC

● Command prompt or power shell

● Shell/command line

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39- Define V8 engine 

It is google’s high-performance open-source Javascript engine which is written in mainly C++ and google. In addition, V8 implements ECMAS script, which is specified on ECMA 262 and runs on Windows 7. 

40- Mention the purpose of require()

It is used for the inclusion of modules from the external files in ExpressJS. Require() is the easiest way of including a module in the express. It requires a function that takes the parameter string for the location of the file. Require() to read the entire javascript file, which executes the file and then returns the exports. 

41- Give the distinction between the cluster and child_process module 

Is the module which has the function set and property to help the developers for forking the processes which they can take the advantage of the multi-core. It can be easily spun on ExpressJS which can communicate with each other in the messaging system. 

42- Name the varieties of a web application that can be built on ExpressJS 

Web applications like single-page, double-page, and hybrid pages can be developed with ExpressJS. 

43- Point the difference between put and patch 

Put has the embedded entity in the modified version of the resources which are deposited on the real serverUnder patch, the information regarding the modification of the original server which holds the time of resourcing for producing the new version is present.
At the time of quotation, people need to forwarding the full payload as requestOnly need to send the parameter at the time of update. 

44- State the reasons for using Zlib in ExpressJS 

The comprehensive library of cross-platform data is zlib. Zlib can be used in ExpressJS for thread pools, HTTPS requests, and compression responses. But for using the zlib, it’s necessary to install the express zlib package. 

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45- Define closures 

It is the function defined in another scope that has access to the variable within the outside range. Thus, the variables present on a global level can be made locally with the closures. 

46- State the meaning of revealing module pattern and also give the syntax

This function is just similar to the module pattern. IT Exposes only the properties and procedures which are returned via the object. The syntax for the revealing module is 

var greeting = ‘Hello world.’

function greet() {



module.exports = {

greet: greet 


47- Give the example of callback function

function callback(err, results// usually we’ll check for the errors before handling results

if(err) {

          //handle error somehow and return


          //no error, perform standard callback handling 


48- Define JIT and state its relation with ExpressJS 

It exists for Just in time. JIT is the program compiler used to send the bytecode to the processes with converting it to instruction. After the writing of the program finishes, the compiler will source the language statement to byte code instead of compiling it all over. With ExpressJS, JIT has improved the execution speed of the code. ExpressJS takes the source coding and converts it to the code of runtime. 

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49- Give the syntax program in pyramid shape for the printing of 0 to N 

function generate Pyramid() {

var totalNumberofRows =5;

var are = new Array();

for (var I = 1;I<= I, j++) {







50- What is the method of generating UUIDs? 

The method are demonstrated below with the syntax 

var uuid = require( ‘node-uuid’);

//Generate a V1 (time based) id uuid.v1();

//Generate a v4 (random) id uuid.v4();
With the last question, the guide of ExpressJS interview questions is completed. We have covered all the basic and advanced-level interview questions on ExpressJS. We hope this guide will help you crack the interview on ExpressJS effectively and conveniently so that you don’t need to search here and there on different websites for the question. These questions are the most common questions which an interviewer may ask to test your capability and skills. So, start your preparation for ExpressJS now and pass your interview with flying colors. 

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