Suggested Certification for Express.js

OpenJS Node.js Application Developer (JSNAD) certification from the OpenJS Foundation

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Interview Questions and Answers

Express.js applications can be deployed to various platforms, including cloud providers like Heroku, AWS, Google Cloud, and Azure. You typically need to set up a server, configure environment variables, and run the application.

You can use middleware like `multer` to handle file uploads. Install it with `npm install multer`.javascript const multer = require(multer); const upload = multer({ dest: uploads/ }); app.post(/upload, upload.single(file), (req, res) => { console.log(req.file); res.send(File uploaded!); });

Express.js is well-suited for building RESTful APIs. You can define routes for each resource (e.g., `/users`), using HTTP methods (GET, POST, PUT, DELETE) to perform CRUD (Create, Read, Update, Delete) operations. Use `res.json()` to return data in JSON format.

You can use middleware functions to handle errors. Define an error-handling middleware after all other routes and middleware. Express uses the number of arguments to a function to know its an error handler (four arguments). Example: javascript app.use((err, req, res, next) => { console.error(err.stack); res.status(500).send(Something broke!); });

Authentication can be implemented using middleware and strategies like JWT (JSON Web Tokens), Passport.js, or custom authentication methods. You typically need to handle user registration, login, and token validation.

The `next()` function passes control to the next middleware function in the stack. Its crucial for moving through the middleware pipeline.

First, install a template engine (e.g., `npm install ejs`). Then, set the view engine and render templates. Example with EJS: javascript app.set(view engine, ejs); app.get(/profile, (req, res) => { res.render(profile, { name: John }); });

Some common middleware packages include: `body-parser` (for parsing request bodies), `morgan` (for logging requests), `cookie-parser` (for handling cookies), `cors` (for handling Cross-Origin Resource Sharing), and `helmet` (for security headers).

You can access request parameters using `req.params` (for route parameters) and `req.query` (for query parameters). Example: javascript app.get(/users/:id, (req, res) => { console.log(req.params.id); res.send(`User ID: ${req.params.id}`); }); app.get(/search, (req, res) => { console.log(req.query.q); res.send(`Search query: ${req.query.q}`); });

You can use the `res.json()` method to send JSON responses. Example: javascript app.get(/data, (req, res) => { res.json({ message: Hello JSON! }); });

You need middleware like `body-parser` to parse form data. First install it: `npm install body-parser`. Then, use it like this: javascript const bodyParser = require(body-parser); app.use(bodyParser.urlencoded({ extended: false })); app.post(/submit, (req, res) => { console.log(req.body); res.send(Form submitted!); });

You can use the `express.static()` middleware to serve static files. Example: javascript app.use(express.static(public)); // Serves files from the public directory

Routers are mini-Express applications that can handle specific routes. They help organize your code by grouping related routes. You can create a router using `express.Router()`.

You can install Express.js using npm (Node Package Manager) with the command: `npm install express`.

Middleware functions are functions that have access to the request object (req), the response object (res), and the next middleware function in the application’s request-response cycle. Middleware functions can perform tasks such as parsing request bodies, logging, authentication, and authorization.

javascript const express = require(express); const app = express(); const port = 3000; app.get(/, (req, res) => {res.send(Hello World!);}); app.listen(port, () => {console.log(`Example app listening at http://localhost:${port}`);});

Routes are defined using HTTP methods (GET, POST, PUT, DELETE, etc.) and a path. For example: javascript app.get(/users, (req, res) => { res.send(List of users); }); app.post(/users, (req, res) => { res.send(Create a new user); });

Express.js supports common HTTP methods like GET, POST, PUT, DELETE, PATCH, OPTIONS, and HEAD.

Express.js is a minimal and flexible Node.js web application framework that provides a robust set of features for web and mobile applications.

Express.js simplifies Node.js web development by providing features like routing, middleware, templating, and error handling. Its fast, unopinionated, and highly customizable.