expressjs Node.js

Express.js is a popular web application framework for Node.js. It is a lightweight and flexible framework that provides a robust set of features for building web applications and APIs.

Express.js is designed to be simple and easy to use, with a minimalistic API that makes it easy to get started. It provides a powerful set of routing and middleware features that allow you to easily handle HTTP requests and responses.

Here's an example of how to create a simple Express.js application:

const express = require('express')
const app = express()

app.get('/', (req, res) => {
  res.send('Hello, world!')
})

app.listen(3000, () => {
  console.log('Server started on port 3000')
})

In this example, we create an Express.js application and define a route for the root URL that sends a "Hello, world!" message back to the client. We then start the server and listen for incoming requests on port 3000.

Express.js also provides a rich set of middleware functions that allow you to add functionality to your application, such as handling cookies, parsing JSON and URL-encoded data, and authenticating users. Middleware functions can be added globally to your application, or to specific routes or groups of routes.

Here's an example of using middleware in an Express.js application:

const express = require('express')
const app = express()

// middleware function to log incoming requests
const logger = (req, res, next) => {
  console.log(`${req.method} ${req.url}`)
  next()
}

app.use(logger)

app.get('/', (req, res) => {
  res.send('Hello, world!')
})

app.listen(3000, () => {
  console.log('Server started on port 3000')
})

In this example, we define a middleware function that logs incoming requests to the console. We then add the middleware function globally to our application using the app.use() method. Any incoming requests will now be logged to the console before being processed by the route handlers.