Express Route Handlers

Introduction

Imagine you're running a post office. Every letter or package needs to be routed to its destination. Express works similarly, acting as the routing system for your web server. In this guide, we will configure Express routes to handle client requests, building on your knowledge of Node's http package.

You'll learn how to handle the following HTTP request types:

GET - Retrieve data
POST - Submit new data
PUT - Update existing data
PATCH - Modify a subset of data
DELETE - Remove data

Setting Up Express

Let’s begin by creating a simple Express application:

const express = require('express');

const app = express();

// Define routes
app.get('/', (req, res) => {
    res.send('Hello from Express!');
});

app.post('/users', (req, res) => {
    res.send('User created!');
});

// Start the server
const port = 8081;
app.listen(port, () => console.log(`Listening on port ${port}...`));

Key Steps:

Create the Express server using express().
Define routes with app.get(), app.post(), etc.
Start the server with app.listen().

Understanding Routes

A route in Express is like a traffic signal directing requests to the right path. Each route matches:

Path: A URI, like /users.
HTTP Method: One of GET, POST, PUT, DELETE, or PATCH.

Here's an example:

app.get('/welcome', (req, res) => {
    res.send('Welcome to our site!');
});

The req (request) object provides details about the client's request, while the res (response) object allows you to send data back.

Dynamic Route Paths

Routes in Express can be dynamic:

Strings: '/users'
Regular Expressions: '/ab+cd'
Arrays: ['/home', '/about']

Example:

let paths = ['/', '/about', '/contact'];

app.get(paths, (req, res) => {
    res.send('This works for multiple paths!');
});

Designing Routes

Good route design makes your application intuitive. Consider these examples for a Twitter-like app:

Path	HTTP Verb	Description
/tweets	GET	Retrieve all tweets
/tweets	POST	Create a new tweet
/tweets/:id	GET	Retrieve a tweet by ID

Sending Responses

Use the res object to send responses:

res.send(): Sends plain text or HTML.
res.json(): Sends JSON data.

Example:

app.get('/json', (req, res) => {
    res.json({
        message: 'Hello, JSON!',
        status: 'success'
    });
});

Testing Your Routes

To test your Express application:

Run your app with node app.js.
Visit http://localhost:8081 in a browser (for GET requests).
Use tools like Postman or Fetch API for other methods:

fetch('/users', {
    method: 'POST',
    headers: { 'Content-Type': 'application/json' },
    body: JSON.stringify({ username: 'NewUser' })
}).then(res => res.json()).then(console.log);

Real-World Applications

Express routes are foundational for:

APIs: Serve JSON data to frontend applications.
Websites: Render HTML pages or serve static files.
Microservices: Create small, single-purpose services.

Example: A task management app could use routes like:

GET /tasks: List all tasks.
POST /tasks: Add a new task.
DELETE /tasks/:id: Remove a task by ID.