Routing

Express.js makes it straightforward to set up a web server, handle routing, and respond to HTTP requests. Here is a basic example of setting up an Express server that responds to GET requests on the root route:

const express = require('express');
const app = express();
 
const HTTP_PORT = process.env.PORT || 8080;
 
app.get('/', (req, res) => {
  res.send('Hello World');
});
 
app.listen(HTTP_PORT, () => console.log(`server listening on: ${HTTP_PORT}`));

From the above code, three essential objects are used to configure the server: app, req, and res.

The Application Object

The app object represents the main application in Express. It provides methods to handle routing, set up middleware, and manage view engines.

app.all()

Registers a callback for a route that matches any HTTP method (GET, PUT, POST, DELETE, etc.).

app.all('/http-testing', (req, res) => {
  res.send('test complete');
});

HTTP Verb Methods

Responds to requests using specific HTTP methods.

app.get('/get-test', (req, res) => {
  res.send('GET Test Complete');
});
 
app.put('/put-test', (req, res) => {
  res.send('PUT Test Complete');
});
 
app.post('/post-test', (req, res) => {
  res.send('POST Test Complete');
});
 
app.delete('/delete-test', (req, res) => {
  res.send('DELETE Test Complete');
});

app.locals

Attaches local variables to the application, persisting throughout the app's lifecycle.

app.locals.title = 'My App';

app.listen()

Starts the HTTP server on a specified port.

const HTTP_PORT = process.env.PORT || 8080;
app.listen(HTTP_PORT, () => {
  console.log('server listening on: ' + HTTP_PORT);
});

app.set()

Assigns a value to a specific setting, useful for configuration like setting the view engine.

app.set('view engine', 'pug');

app.use()

Adds middleware to the application, executing functions globally or on specific routes before route handlers.

app.use((req, res, next) => {
  console.log('Middleware running...');
  next();
});

The Request Object

The req object contains information and metadata about the request sent to the server. It is typically referred to as req.

req.body

Contains data submitted in the request body. Requires body-parsing middleware.

app.post('/urlencoded-test', (req, res) => {
  res.send(req.body);
});

req.cookies

Contains cookie data sent by the client. Requires cookie-parsing middleware.

// Cookie: name=tj
console.log(req.cookies.name); // "tj"

req.params

Contains route parameters specified in the URL.

app.get('/employee/:employeeNum', (req, res) => {
  res.send(`Employee Number: ${req.params.employeeNum}`);
});

req.query

Contains query string parameters in the URL.

app.get('/products', (req, res) => {
  let result = 'all Products';
  if (req.query.onSale == 'true') {
    result += ' (on sale)';
  }
  res.send(result);
});

req.get()

Gets the value of specific HTTP headers sent with the request.

app.get('/hello', (req, res) => {
  res.send(`Hello ${req.get('user-agent')}`);
});

The Response Object

The res object contains information and metadata about the response sent from the server. It is typically referred to as res.

res.cookie()

Sends a cookie with the response. A cookie is a small piece of data sent from a server and stored on the user's browser to remember information about the user.

app.get('/cookie-test', (req, res) => {
  res.cookie('message', 'Hello World!');
  res.send('Cookie Sent!');
});

res.end()

Ends the response process, sending no content.

app.put('/update', (req, res) => {
  res.status(204).end();
});

res.redirect()

Redirects the client to another URL.

app.get('/to-google', (req, res) => {
  res.redirect('https://www.google.ca/');
});

res.send()

Sends a response to the client. Can send a string, object, array, or buffer.

app.get('/json-test', (req, res) => {
  res.send({ message: 'Hello World!' }); // Content-Type: application/json; charset=utf-8
});
 
app.get('/plain-text-test', (req, res) => {
  res.send('Hello World!'); // Content-Type: text/html; charset=utf-8
});

res.sendFile()

Sends a file as a response.

app.get('/', (req, res) => {
  res.sendFile(path.join(__dirname, '/views/home.html'));
});

res.status()

app.put('/update', (req, res) => {
  res.status(204).end();
});