express()

The main Express module exports and factory function

The express module exports the Express factory function and various utility functions and constructors.

express()

Creates an Express application. The express() function is the top-level function exported by the express module.

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

Example

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

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

app.listen(3000);

Exported Properties

The express module exports several additional properties for creating routers, middleware, and accessing prototypes.

express.application

The Application prototype, which is used to extend the app object.

const express = require('express');
const app = express.application;

express.request

The Request prototype, used to extend req objects.

const express = require('express');
const req = express.request;

express.response

The Response prototype, used to extend res objects.

const express = require('express');
const res = express.response;

Exported Constructors

express.Router([options])

Creates a new router object. A router behaves like middleware and can be used to organize routes.

Example

const express = require('express');
const router = express.Router();

router.get('/users', (req, res) => {
  res.send('Users list');
});

app.use('/api', router);

express.Route

Exposed Route constructor from the router module. Used internally by Express.

Exported Middleware

Express exports several built-in middleware functions from external packages.

express.json([options])

Middleware that parses incoming requests with JSON payloads. Based on body-parser.

Example

app.use(express.json());

app.post('/api/users', (req, res) => {
  console.log(req.body); // Access parsed JSON
  res.json({ received: true });
});

express.urlencoded([options])

Middleware that parses incoming requests with URL-encoded payloads. Based on body-parser.

Example

app.use(express.urlencoded({ extended: true }));

app.post('/login', (req, res) => {
  const { username, password } = req.body;
  res.send(`Login attempt for ${username}`);
});

express.raw([options])

Middleware that parses incoming request payloads into a Buffer. Based on body-parser.

Example

app.use(express.raw({ type: 'application/octet-stream' }));

app.post('/upload', (req, res) => {
  console.log(req.body); // Buffer
  res.send('Received');
});

express.text([options])

Middleware that parses incoming request payloads into a string. Based on body-parser.

Example

app.use(express.text());

app.post('/notes', (req, res) => {
  console.log(req.body); // String
  res.send('Note saved');
});

express.static(root, [options])

Serves static files from the specified directory. Based on serve-static.

Example

app.use(express.static('public'));
app.use('/static', express.static('public'));

// Serve with options
app.use(express.static('public', {
  maxAge: '1d',
  dotfiles: 'ignore',
  index: 'index.html'
}));

Complete Example

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

// Use built-in middleware
app.use(express.json());
app.use(express.urlencoded({ extended: true }));
app.use(express.static('public'));

// Create a router
const router = express.Router();
router.get('/users', (req, res) => {
  res.json([{ id: 1, name: 'John' }]);
});

app.use('/api', router);

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