Top 10 Interview Question On Express.JS

Introduce to Interview Question On Express.JS

Whether you’re a developer fresh out of college or someone looking to change jobs, you are bound to go through mandatory interviews to do so. Given that Express.js represents a back-end extension of Node.js, which is quite popular due to its open-source nature, you will likely be asked about it.

According to published data, 43% of developers use Node.js for enterprise-level applications, while 85% primarily use it for web app development. As its extension, Express.js is bound to rear its head during your next job interview, making proper preparation important. Let’s cover several Express.js questions you are bound to face during job hunting, whether you go after freelance gigs or long-term IT employment.

What exactly is Express.js?

Depending on the kind of position you apply for, your interviewer will either start with the very basics or jump straight into problem-solution type questions. If the former is the case, you should be prepared to quickly and succinctly explain what Express.js actually is to your interviewer. Express.js is an open-source Node.js-based web app framework designed for building web apps and APIs.

Express.js is written in JavaScript and has been in development since 2010. As such, many popular development frameworks have sprouted from Express.js, including Feathers, Blueprint, and Kites, which you can also learn to use for your job. It’s important that you exhibit interest and passion not only for Node.js but also for app development as a whole during the interview. This, more than anything, will determine whether the employer moves forward with your application.

Which features does Express.js contain?

Like with any development framework, Express.js comes packed with a number of features which make its use worthwhile. In the case of Express.js, some of the features you should be aware of for your interview are:

It can style single page, multi-page as well as hybrid web apps

It allows for middleware set up to respond to HTTP requests

It can dynamically render HTML pages based on templates

It features high-performance I/O

It features MVC architecture support for web applications

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The feature list of Express.js is, of course, comprehensive, but these are the points you should hit during your interview more than others. Any of these elements, if listed, can become sub questions and discussion topics on their own, so be prepared to talk about their practical application. If you used Node.js in tandem with Express.js previously, you can create a portfolio of sorts on GitHub and showcase your work to potential employers.

What is a Cookie, and what purpose does it fulfill?

If you’re applying for a web-based development project, you will likely have to set up Cookies on your client’s or employer’s website. Express.js does feature a cookie-parser middleware, which you can install on the app and, in turn, activate Cookies on whichever freelance project you work on.

To answer the question, Cookies are a form of client-side data which retains information of a user’s action. The functionality of Cookies is to help personalize the user’s experience on the app or website, track their browsing patterns, and better manage their sessions. It is an extremely useful form of UX personalization, which can be helpful for eCommerce apps or websites as well as any other content-rich platform.

What do we mean by Scaffolding in Express.js?

As with any other framework, Express.js will require you to rely on established terminology and lingo during development. Interviewers will likely test your knowledge of these terms and their proper usage, starting with the likes of Scaffolding. Scaffolding is a process of creating the base form of application development environment so that you can start building the app properly.

Express.js features Yeoman as a Scaffolding tool built for Node.js and, as such, is actively used by the former. The framework also features an express application generator, which is a command set that can create a list of files and folders default to Express.js. If given the opportunity, you can write the command down for your interviewer and list the files/folders it generates:

npm install express-generator –g
express myTestExpressApp

This will generate: bin (folder), public (folder), routes (folder), views (folder), app.js (file), package.json (file)

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What exactly is Middleware, and what can we do with it?

Middleware represents a function in Express.js, which is used to perform a number of different actions depending on the current point in development. Some of the actions you can perform via Middleware are:

Code execution

Changes to request and response objects

Ending request-response cycles

Moving on to the next Middleware function in your stack

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There are also different forms of Middleware which you can integrate into your development framework. You should be familiar with these during interview, and you can learn more about them if your hiring goes forward:

Built-in Middleware function

Error-handling Middleware function

Application-level Middleware function

Router-level Middleware function

Third-party Middleware function


What do we mean by Routing in Express.js?

Routing is the process of the application’s or website’s response to a client-side request made on the platform. Routing refers to a particular URI endpoint and a specific HTTP request method, where each function is executed when its route is matched. Let’s look at a very simple example of a route as seen in Express.js development:

var express = require(‘express’)
var app = express()


// respond with “hello world” when a GET request is made to the homepage
app.get(‘/’, function (req, res) {
res.send(‘hello world’)

Again, this example can be used during your application to showcase your handle of Express.js, but you should learn more about Routing following the interview.

Which database integrations does Express.js feature?

Express.js feature
Express.js feature


Regardless of whether you work as a freelancer or a long-term developer, you will definitely come across database integration tasks. Express.js is highly flexible in this regard, so make sure to familiarize yourself with the following databases and their relation to the following before your interview:



SQL Server


While these are not all of the databases supported by Express.js, they will be enough to help you pass through the interview more easily. Given the nature of web and app development, it’s also likely that you will work with other developers more familiar with database management. Thus, your focus should lie in Node.js and Express.js, first and foremost, to improve your odds at employment.

Which arguments are available in Express.js?

This is a simple but important question which might pop up while you talk about Routing with the interviewer. Express.js features three simple arguments which can be inserted based on the desired developer action:

Res – response object

Req – request object

Next – argument used in case of passing management to one of the previous two arguments (switching)

Depending on who you ask, the third argument can but doesn’t have to be mentioned during the interview. The reasoning behind this lies in the fact that it doesn’t perform any action other than switching between other arguments. It’s up to you how thorough of an answer you want to give at that point.

How would you configure application properties via Express.js?

configure application properties via Expressjs
configure application properties via Expressjs

We can edit application properties in one of two ways when developing a website or app with Express.js. You can configure properties through Process.env or through RequireJs, respectively. The choice between the two will fall down to personal preference and your own expertise.

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Create a file with the .env extension inside your project folder and add all of the initial properties to it. Subsequently, use the following string to access the properties and modify them:

var host=process.env.APP_HOST;


Simply create a file ‘config.json’ inside ‘config’ folder of your project folder, then add config properties in ‘config.json’ file. Subsequently, use the require keyword to access the ‘config.json’ file.

How can we debug in Express.js?

Finally, you will likely be asked about debugging in Express.js and how to do it quickly. There is a simple answer to this question, which depends on the platform you develop the app on. The two commonly used debugging methods in Express.js are:


node app.js


set DEBUG=express:*
node app.js

Final Notes

The best way to prepare for your next interview with Express.js in mind is to get in touch with the development community behind the framework. Express.js features a plethora of tutorials and how-to guides, ranging from basic functionality to advanced integration and coding tips and tricks.

Consider the questions we’ve discussed during your own interview and try to expand on the answers with your own experience and insight. Interviewers love nothing more than to talk to creative developers with innovative ideas on how to use existing development frameworks in interesting ways.

Bio: Kristin Savage is a professional content writer, editor, and tech aficionado. She spends her working hours writing articles and case studies on IT, digital marketing, and business development topics. Kristin is a valued contributor to, a source of free essay samples and flashcards for students in need of writing help. In her spare time, Kristin enjoys dabbling into programming and enjoys spending time outdoors.

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