Expressjs Backend Developer Interview Questions
Express.js is a routing and Middleware framework for handling the different routing of the webpage and it works between the request and response cycle. Middleware gets executed after the server receives the request and before the controller actions send the response.
The basic syntax for the middleware functions are as follows –
app.get(path, (req, res, next) => {}, (req, res) => {})
In Express.js, request and response objects are fundamental to handling HTTP requests and generating HTTP responses. Here’s how Express.js handles these objects:
- Request Object (req):
- The request object (
req) represents the HTTP request received from the client. It contains information about the request, such as the HTTP method, URL, headers, query parameters, request body, and more. - Express populates the request object with this information and passes it to route handlers and middleware functions.
- The request object (
- Response Object (res):
- The response object (
res) represents the HTTP response that Express sends back to the client. It allows developers to send back data, set HTTP headers, and control the response status code. - Express provides methods on the response object to send different types of responses, such as sending JSON data (
res.json()), sending HTML (res.send()), redirecting the client to a different URL (res.redirect()), setting HTTP headers (res.setHeader()), and more.
- The response object (
Node.js server code sets up a RESTful API for managing data. It provides endpoints for performing CRUD (Create, Read, Update, Delete) operations on a collection of records. The server uses the Express.js framework to handle HTTP requests.
24. What is the difference between a traditional server and an Express.js server?
Traditional server | Express.js server |
|---|---|
| Typically, traditional servers are built using various server-side technologies and frameworks, such as Java with Spring, Python with Django, Ruby on Rails, ASP.NET, etc. | Express.js is a minimal and flexible Node.js web application framework. It is specifically designed for building web applications and APIs using JavaScript on the server side. |
| Traditional servers may use a synchronous or asynchronous programming model, depending on the underlying technology. | Express.js is built on top of Node.js, which uses an event-driven, non-blocking I/O model. Asynchronous programming is fundamental to Node.js and, by extension, to Express.js. |
| Frameworks like Spring or Django often come with built-in middleware and routing systems. | Express.js also provides middleware and routing, but it has a more lightweight and flexible approach. Middleware functions can be added to the request-response cycle to perform specific tasks. |
| Different server-side frameworks have their own communities, ecosystems, and plugins. The size and activity of these communities can vary depending on the framework. | Express.js has a large and active community. It is one of the most popular Node.js frameworks, and as such, it benefits from a rich ecosystem of middleware, plugins, and extensions. |
A JSON web token(JWT) is JSON Object which is used to securely transfer information over the web(between two parties). It can be used for an authentication system and can also be used for information exchange. The token is mainly composed of header, payload, signature.
Publisher Subscriber basically known as Pub-Sub is an asynchronous message-passing system that solves the drawback above. The sender is called the publisher whereas the receiver is called the subscriber. The main advantage of pub-sub is that it decouples the subsystem which means all the components can work independently.
POST parameter can be received from a form using express.urlencoded() middleware and the req.body Object. The express.urlencoded() middleware helps to parse the data that is coming from the client-side.
Example: Here, is the code to get post a query in Express.js
const express = require('express');
const app = express();
// Parse incoming request bodies with urlencoded payloads
app.use(express.urlencoded({ extended: true }));
// POST route to handle form submission
app.post('/submit', (req, res) => {
// Extract data from the request body
const { name, email } = req.body;
// Process the data (in this example, just logging it)
console.log('Received form submission:');
console.log('Name:', name);
console.log('Email:', email);
// Respond with a success message
res.send('Form submitted successfully');
});
// Start the server
const port = process.env.PORT || 3000;
app.listen(port, () => {
console.log(`Server is running on port ${port}`);
});
Explanation:
- We use
app.use(express.urlencoded({ extended: true }))to enable theexpress.urlencoded()middleware, which parses incoming request bodies withapplication/x-www-form-urlencodedformat. - We define a POST route
/submitto handle form submissions. Inside the route handler, we extract thenameandemailparameters from thereq.bodyobject, which is populated by theexpress.urlencoded()middleware. - We process the received data (in this example, just logging it to the console).
- We respond with a success message using
res.send().
Scaffolding is creating the skeleton structure of application. It allows users to create own public directories, routes, views etc. Once the structure for app is built, user can start building it.
Syntax:
npm install express --save
Error handling in Express.js refers to the process of capturing and responding to errors that occur during the execution of an Express application. In Express, you can handle errors using middleware functions, which are functions that have access to the request and response objects, as well as the next middleware function in the application’s request-response cycle.
Template Engine : A template engine basically helps us to use the static template files with minimal code. At runtime, the template engine replaces all the variables with actual values at the client-side.
To use templating with Express.js in Node.js:
- Install a template engine like EJS (
npm install ejs). - Set up Express to use the template engine (
app.set('view engine', 'ejs')). - Create EJS templates in the
viewsdirectory. - Render EJS templates in Express routes using
res.render(). - Pass dynamic data to the templates.
- Start the Express server.
Backend Developer Interview Questions
Backend development involves working on the server side of web applications, where the logic, database interactions, and server management take place. It focuses on handling data, processing requests from clients, and generating appropriate responses.
In this Top Backend Development interview questions, We cover Interview questions from all important topics from basic to advanced such as JavaScript, Node.js, Express.js, SQL, MongoDB, Django, PHP, Java Spring, and API. No matter whether you are a fresher or an experienced professional we have got questions that will enhance your skills and help you shine in your backend development interview.
Contact Us