Top 25+ Express.Js Interview Questions & Answers
By: Saurabh Samir
Tags: JavaScript, Interview Questions, Programming Languages, Expressjs, Nodejs

You’re probably aware that JavaScript is the programming language most often used to add interactivity to the front end of a website, but its capabilities go far beyond that — entire sites can be built on JavaScript, extending it from the front to the back end, seamlessly.

Express.js and Node.js gave JavaScript newfound back-end functionality — allowing developers to build software with JavaScript on the server side for the first time. Together, they make it possible to build an entire site with JavaScript: You can develop server-side applications with Node.js and then publish those Node.js apps as websites with Express.

Because Node.js itself wasn’t intended to build websites, the Express framework is able to layer in built-in structure and functions needed to actually build a site. It’s a pretty lightweight framework that’s great for giving developers extra, built-in web application features and the Express API without overriding the already robust, feature-packed Node.js platform. In short, Express and Node are changing the way developers build websites.

EXPRESS.JS FRAMEWORK BASICS

Server-side web and mobile application framework

Language: written in JavaScript

Express builds:

i. Single-page, multi-page, and hybrid mobile and web apps

ii. Common back-end functions for web applications

iii. APIs (application programming interfaces)

Templating engines : Express comes with two templating engines, Jade and EJS, which facilitate the flow of data into a website structure. MVC pattern : Express supports the Model-View-Controller architecture, a really helpful way to build websites in a model-driven format. Platform : Node.js Operating system : It’s cross-platform, so it’s not limited to one OS. The Express Generator lets you create complex applications quickly.

How Express.js works

Here is a block scheme on how Express.js works with Node.js and MongoDB

Node.js is an event-driven server, that has a single thread which manages all connections to the server. It processes all the requests in the callbacks without delaying their flow.

As you can see from the picture above, when the request enters the server, Express processes it into the callback without blocking the main stack.

Imagine that you need to retrieve some data from the file or database. Such process may be time-consuming (for example because of disc read delay). The average server will block all other requests until these data are delivered.

Node JS, in its turn, registers the logic of data post-processing in the callback. Data are processed in parallel, so the server can accept another data at the same time. As the result, Node.js can process the bigger amount of requests more efficiently.

Mongoose is the Mongo driver add-in, that perfectly fits the Express ecosystem. The main advantage of MongoDB is that it is JavaScript oriented. It means that the driver transfers all the data they are without wasting time on adjusting them to the programming environment. MongoDB is developed for scale-out data-driven servers.

Each request in MongoDB is processed in the same way as in the callback. It means that the server doesn’t have to wait (block the stock) until the certain data are transferred and can process other requests simultaneously. It is extremely important because the scale-out database can be situated on one or several physically remote servers, so retrieving data from them is time-sapping.

Now let’s conclude the whole process once again. Server receives the request and registers the event data processing. Then the event sends the request to the remote Mongo server. After this is done, some time is needed for data to return. Simultaneously, the server is processing other requests. When the data arrives, Mongo driver invokes the user request handler. The user request handler delivers the data back to the client.

This blog provides Frequently asked Top 25+ Express.Js interview questions and best answers for freshers and 2–4 year experienced developers.

1. What is Express Js? What are core features of Express framework?

Express JS is a framework which helps to develop web and mobile applications. Its works on node.js plateform. Its sub part of node.js.

Express JS Features:

Following are some of the core features of Express framework ?

Set up middlewares in order to respond to HTTP/RESTful Requests.

It is possible to defines a routing table in order to perform different HTTP operations.

Dynamically renders HTML Pages based on passing arguments to templates.

Provides all the feature provides by core Node.js.

Express prepare a thin layer, therefore, the performance is adequate.

Organize the web application into an MVC architecture.

Manages everything from routes to rendering view and preforming HTTP request.

2. What type of web application can built using Express JS?

you can build single-page, multi-page, and hybrid web applications.

3. What are core features of Express framework?

Allows to set up middle-wares to respond to HTTP Requests.

Defines a routing table which can works as per HTTP Method and URL.

Dynamically render HTML Pages.

4. Why I should use Express JS?

Express 3.x is a light-weight web application framework to help organize your web application into an MVC architecture on the server side.

More Interview Questions on Express JS Visit : https://learnfrenzy.com/blog/top-25-expressjs-interview-questions--answers