In this article, let’s learn and master the top 30 expressjs interview questions and answers with practical code examples.
ExpressJS is a popular web application framework for Node.js that simplifies the process of building robust and scalable web applications.
As the demand for ExpressJS developers continues to rise, it’s important to prepare for interviews with questions that are commonly asked in the industry.
In this article, we have compiled a list of the top 30 ExpressJS interview questions that you may encounter during your job search.
Whether you are a beginner or an experienced developer, this guide will provide you with the necessary knowledge to ace your ExpressJS interview and land your dream job.
1. What is Express.js?
Answer: Express.js is a web application framework for Node.js. It provides a set of features for building web applications and APIs, such as routing, middleware, templating, and database integration.
2. What are the advantages of using Express.js?
Answer: Some advantages of using Express.js are:
- It is lightweight and flexible, allowing developers to create web applications quickly and easily.
- It supports various middleware and third-party modules, making it easy to integrate with other tools and services.
- It provides a simple and intuitive API for handling HTTP requests and responses.
- It allows for easy creation of RESTful APIs and web services.
3. How do you create a basic Express.js application?
Answer: To create a basic Express.js application, you can use the following code:
const express = require('express');
const app = express();
app.get('/', (req, res) => {
res.send('Hello, World!');
});
app.listen(3000, () => {
console.log('Server listening on port 3000');
});
4. What is middleware in Express.js?
Answer: Middleware in Express.js is a function that handles requests and responses in the middleware chain. It can be used to perform actions such as logging, authentication, validation, and error handling. Middleware functions are executed sequentially in the order they are added to the middleware stack.
5. How do you use middleware in Express.js?
Middleware can be added to an Express.js application using the use method. For example, to add a logging middleware, you can use the following code
app.use((req, res, next) => {
console.log(`${req.method} ${req.url}`);
next();
});
6. What is routing in Express.js?
Answer: Routing in Express.js is the process of mapping HTTP requests to corresponding handler functions. It allows developers to define a set of routes for an application and specify what happens when each route is accessed.
7. How do you define routes in Express.js?
Answer: Routes can be defined using the get, post, put, delete, and other HTTP methods in Express.js. For example, to define a route that handles a GET request to the /users path, you can use the following code:
app.get('/users', (req, res) => {
res.send('List of users');
});
8. What is template engine in Express.js?
Answer: A template engine in Express.js is a module that allows developers to render dynamic HTML pages using templates. It allows for the separation of HTML and code, making it easier to maintain and modify web pages.
9. What are some popular template engines in Express.js?
Answer: Some popular template engines in Express.js are Pug (formerly known as Jade), EJS (Embedded JavaScript), and Handlebars.
10. How do you integrate a template engine in Express.js?
To integrate a template engine in Express.js, you need to install the corresponding module and set it as the default view engine for the application. For example, to use Pug as the template engine, you can use the following code:
const express = require('express');
const app = express();
app.set('view engine', 'pug');
11. What is a middleware stack in Express.js?
Answer: A middleware stack in Express.js is a series of middleware functions that are executed sequentially for every HTTP request that matches a particular route. The middleware stack is built using the use method and can include any number of middleware functions.
12. How do you handle errors in Express.js?
Answer: Errors in Express.js can be handled using middleware functions that have four arguments (err, req, res, next). These functions are executed whenever an error is thrown or passed to the next function. For example, to handle a 404 error, you can use the following code:
app.use((req, res, next) => {
res.status(404).send('Sorry, page not found');
});
13. What is the difference between req.params and req.query in Express.js?
Answer: req.params is an object that contains route parameters extracted from the URL, while req.query is an object that contains query parameters passed in the URL after the ? character. For example, if the URL is /users/:id?name=John, req.params.id would be set to the value of :id, while req.query.name would be set to 'John'.
14. How do you handle file uploads in Express.js?
File uploads in Express.js can be handled using middleware functions that support multipart/form-data. The multer middleware is a popular module used for handling file uploads. For example, to handle a file upload, you can use the following code
const multer = require('multer');
const upload = multer({ dest: 'uploads/' });
app.post('/upload', upload.single('file'), (req, res) => {
res.send('File uploaded successfully');
});
15. What is a cookie in Express.js?
Answer: A cookie in Express.js is a small piece of data that is sent from a web server to a web browser and stored on the client’s machine. Cookies are commonly used for authentication, session management, and user preferences.
16. How do you handle cookies in Express.js?
Cookies can be handled in Express.js using the cookie-parser middleware. For example, to set a cookie, you can use the following code:
const cookieParser = require('cookie-parser');
app.use(cookieParser());
app.get('/setcookie', (req, res) => {
res.cookie('username', 'John Doe');
res.send('Cookie set successfully');
});
17. What is a session in Express.js?
A session in Express.js is a way to store data about a user across multiple requests. It allows for stateful communication between the server and client and is commonly used for authentication and user management.
18. How do you handle sessions in Express.js?
Answer: Sessions can be handled in Express.js using the express-session middleware. For example, to set up a session, you can use the following code:
const session = require('express-session');
app.use(session({ secret: 'mysecretkey' }));
app.get('/setsession', (req, res) => {
req.session.username = 'John Doe';
res.send('Session set successfully');
});
19. How do you create a new Express.js application?
Answer: To create a new Express.js application, you can use the express command-line interface (CLI) tool. First, install the tool globally by running npm install -g express-generator. Then, run express myapp to generate a new Express.js application named myapp. Finally, navigate into the myapp directory and run npm install to install the dependencies.
20. How do you create a new route in Express.js?
Answer: To create a new route in Express.js, you can use the app.get, app.post, app.put, app.delete, or app.all methods. For example, to create a route that responds to a GET request to /hello, you can use the following code:
app.get('/hello', (req, res) => {
res.send('Hello, World!');
});
21. How do you access route parameters in Express.js?
Answer: Route parameters can be accessed using the req.params object. For example, to create a route that responds to a GET request to /users/:id, you can use the following code:
app.get('/users/:id', (req, res) => {
const userId = req.params.id;
res.send(`User ID: ${userId}`);
});
22. How do you handle JSON data in Express.js?
Answer: JSON data can be handled using the express.json() middleware. For example, to handle a JSON POST request to /users, you can use the following code:
app.use(express.json());
app.post('/users', (req, res) => {
const userData = req.body;
// Handle the user data
});
23. How do you handle form data in Express.js?
Answer: Form data can be handled using the express.urlencoded() middleware. For example, to handle a POST request to /users with form data, you can use the following code:
app.use(express.urlencoded({ extended: true }));
app.post('/users', (req, res) => {
const userData = req.body;
// Handle the user data
});
24. How do you serve static files in Express.js?
Static files can be served using the express.static middleware. For example, to serve static files from the public directory, you can use the following code:
app.use(express.static('public'));
25. How do you use templates in Express.js?
Answer: Templates can be used in Express.js using template engines such as EJS, Pug, or Handlebars. For example, to use EJS as the template engine, you can use the following code:
app.set('view engine', 'ejs');
app.get('/hello', (req, res) => {
res.render('hello', { name: 'John' });
});
26. How do you handle errors in Express.js?
Answer: Errors can be handled using middleware functions that have four arguments (err, req, res, next). These functions are executed whenever an error is thrown or passed to the next function. For example, to handle a 404 error, you can use the following code:
app.use((req, res, next) => {
res.status(404).send('Sorry, page not found');
});
27. How do you use cookies in Express.js?
Answer: Cookies can be handled using the cookie-parser middleware. First, install the middleware by running npm install cookie-parser. Then, use it in your Express.js application as follows:
const cookieParser = require('cookie-parser');
app.use(cookieParser());
app.get('/set-cookie', (req, res) => {
res.cookie('name', 'John');
res.send('Cookie has been set');
});
app.get('/get-cookie', (req, res) => {
const name = req.cookies.name;
res.send(`Cookie value: ${name}`);
});
28. How do you handle sessions in Express.js?
Answer: Sessions can be handled using the express-session middleware. First, install the middleware by running npm install express-session. Then, use it in your Express.js application as follows:
const session = require('express-session');
app.use(session({
secret: 'my-secret-key',
resave: false,
saveUninitialized: true
}));
app.get('/set-session', (req, res) => {
req.session.name = 'John';
res.send('Session has been set');
});
app.get('/get-session', (req, res) => {
const name = req.session.name;
res.send(`Session value: ${name}`);
});
29. How do you authenticate users in Express.js?
Answer: Users can be authenticated using middleware functions that verify the user’s credentials and set the req.user property. For example, to authenticate users using a username and password, you can use the following code:
app.post('/login', (req, res) => {
const { username, password } = req.body;
// Authenticate the user
if (authenticated) {
req.user = { username };
res.redirect('/');
} else {
res.send('Invalid username or password');
}
});
app.get('/', (req, res) => {
if (req.user) {
res.send(`Welcome, ${req.user.username}`);
} else {
res.redirect('/login');
}
});
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