Edge Computing with Cloudflare Workers & Deno · Lesson

Routing & Middleware

Utilize routing libraries and middleware patterns to organize and enhance your Worker API.

Routing & Middleware is a free Edge Computing with Cloudflare Workers & Deno lesson on CoddyKit — lesson 2 of 3. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the Edge Computing with Cloudflare Workers & Deno learning path, one of 3 lessons in the course, and your progress syncs across the web and the CoddyKit app.

API Routing Essentials

When building APIs, we need a way to direct incoming requests to the correct functions based on their URL path and HTTP method (GET, POST, etc.). This process is called routing.

Think of it like a receptionist for your API. When a request comes in, the router checks its destination and sends it to the right department (your code handler).

Manual Worker Routing

In a Cloudflare Worker, all incoming requests are handled by the fetch event listener. You can manually inspect the request's URL and method to decide what to do.

While possible for simple cases, this approach quickly becomes complex and hard to manage as your API grows.

export default {
  async fetch(request) {
    const url = new URL(request.url);
    if (url.pathname === '/hello' && request.method === 'GET') {
      return new Response('Hello from manual route!');
    }
    return new Response('Not Found', { status: 404 });
  }
}

Introducing itty-router

To simplify routing, we use lightweight libraries. For Cloudflare Workers, itty-router is a popular choice. It's tiny, fast, and designed for the edge.

It provides a clean, expressive way to define routes and handlers, making your Worker code much more organized.

Basic GET Routes

With itty-router, you can define routes using methods like router.get() for GET requests. Each route takes a path and a handler function.

Let's create a simple Worker that responds to / and /greet.

import { Router } from 'itty-router';

const router = Router();

router.get('/', () => new Response('Welcome to the API!'));
router.get('/greet', () => new Response('Hello there!'));

export default {
  fetch: router.handle
};

Handling All HTTP Methods

itty-router allows you to define routes for specific HTTP methods like .post(), .put(), .delete(), and more.

You can also use .all() to match any HTTP method for a given path, useful for middleware or generic handlers.

import { Router } from 'itty-router';

const router = Router();

router.get('/data', () => new Response('GET data'));
router.post('/data', () => new Response('POST data', { status: 201 }));
router.all('*', () => new Response('Method Not Allowed', { status: 405 }));

export default {
  fetch: router.handle
};

Dynamic Route Parameters

Often, you need to extract dynamic values from the URL, like an item ID or a username. These are called route parameters.

itty-router uses a colon (:) to define parameters in a route path. The values are then available in the handler's request.params object.

import { Router } from 'itty-router';

const router = Router();

router.get('/users/:id', ({ params }) => {
  return new Response(`Fetching user ${params.id}`);
});

export default {
  fetch: router.handle
};

What is Middleware?

Middleware functions are code snippets that run before or after your main route handler. They can modify the request, perform logging, check authentication, or add headers to the response.

They act as a pipeline, allowing you to add common functionalities across multiple routes without duplicating code.

Implementing Simple Middleware

With itty-router, middleware can be added to specific routes or globally. A middleware function receives the request and can return a response (ending the chain) or continue to the next handler.

Let's add a simple logging middleware that runs for every request.

import { Router } from 'itty-router';

const router = Router();

const loggerMiddleware = async (request, event) => {
  console.log(`Request: ${request.method} ${request.url}`);
  // To proceed to the next handler, don't return a Response.
  // If you return a Response, the chain stops.
};

router.all('*', loggerMiddleware);
router.get('/hello', () => new Response('Hello from route!'));

export default {
  fetch: router.handle
};

Chaining Middleware

You can chain multiple middleware functions. Each middleware executes in order. If a middleware doesn't return a response, the next one in the chain (or the final route handler) is called.

This allows for powerful, modular processing of requests, like authentication, data parsing, and logging.

import { Router } from 'itty-router';

const router = Router();

const authMiddleware = async (request) => {
  if (request.headers.get('Authorization') !== 'Bearer token123') {
    return new Response('Unauthorized', { status: 401 });
  }
};

const headerMiddleware = async (request, event) => {
  // Add a custom header to the response later
  event.response = new Response('', { headers: { 'X-Powered-By': 'CoddyKit' } });
};

router.get('/secure', authMiddleware, (request) => {
  return new Response('Access granted!');
});
router.get('/info', headerMiddleware, (request) => {
  return new Response('Info page');
});

export default {
  fetch: async (request, env, ctx) => {
    const response = await router.handle(request, env, ctx);
    // Merge headers from middleware if present
    if (ctx.response && response) {
      for (let [key, value] of ctx.response.headers.entries()) {
        response.headers.set(key, value);
      }
    }
    return response;
  }
};

Routing & Middleware Check

Consider a Cloudflare Worker using itty-router. You want to ensure that all requests to /admin/* paths require an X-Admin-Key header, and if it's missing, return a 403 Forbidden response. Other paths should not be affected.

Recap: Routing & Middleware

You've mastered the fundamentals of organizing your edge API with routing and middleware!

Routing directs requests to the right handlers.
Libraries like itty-router simplify route definition, including dynamic parameters.
Middleware functions enhance requests/responses, adding common logic like logging or authentication before (or after) the main handler.

These patterns are crucial for building scalable and maintainable serverless APIs at the edge.

Frequently asked questions

Is the “Routing & Middleware” lesson free?

Yes — the full text of “Routing & Middleware” is free to read here on the web, and the Edge Computing with Cloudflare Workers & Deno course includes 3 lessons in total. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the Edge Computing with Cloudflare Workers & Deno course, upgrade to CoddyKit PRO.

What will I learn in “Routing & Middleware”?

Utilize routing libraries and middleware patterns to organize and enhance your Worker API. You practise Edge Computing with Cloudflare Workers & Deno with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.

Do I need any experience to start Edge Computing with Cloudflare Workers & Deno?

No prior experience is required. Edge Computing with Cloudflare Workers & Deno on CoddyKit is structured for beginners through advanced learners; this is — lesson 2 of 3, so you can start here or from the beginning and move at your own pace.

How long does the “Routing & Middleware” lesson take?

Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.

Can I write and run code in this Edge Computing with Cloudflare Workers & Deno lesson?

Yes. Every Edge Computing with Cloudflare Workers & Deno lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.

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