Deno on Cloudflare Workers

Welcome! In this lesson, we'll explore how to bring the power of Deno to Cloudflare Workers. This integration lets you leverage Deno's modern runtime features while benefiting from Workers' global edge network.

You'll learn how to prepare your Deno code so it can run seamlessly on Cloudflare's serverless platform.

Cloudflare Workers run in a V8 JavaScript engine environment. While Deno also uses V8, it adds its own APIs (like Deno.readTextFile, Deno.serve) and a secure permission model.

These Deno-specific APIs aren't directly available in the standard Worker runtime. So, how do we make Deno code compatible?

The first key step is transpilation. This is the process of converting source code from one language or version to another while maintaining its functionality.

• TypeScript to JavaScript: Deno often uses TypeScript. Workers need plain JavaScript. Transpilation converts your .ts files to .js.
• Modern JS to Older JS: Sometimes, newer JavaScript features might be transpiled down for broader compatibility.

Imagine you have a Deno utility written in TypeScript:

// my_util.ts
export function calculateSum(a: number, b: number): number {
  return a + b;
}

During transpilation, this becomes standard JavaScript, removing type annotations:

// my_util.js (after transpilation)
export function calculateSum(a, b) {
  return a + b;
}

This JavaScript is now understood by the Worker runtime.

The second crucial step is bundling. This combines multiple JavaScript modules and their dependencies into a single, optimized JavaScript file.

• Single File: Workers are often deployed as a single JavaScript file.
• Performance: Bundling reduces the number of files the runtime needs to load, improving startup time.
• Dependency Management: It resolves and includes all necessary code from imported modules.

Here's a simple Deno function. In a real project, this might be in its own module (e.g., utils.ts) and imported. For now, let's see it run directly:

Imagine we have our getGreeting function from the previous scene, perhaps in a file called src/utils.ts, and our main Worker logic in src/worker.ts that imports it.

// src/worker.ts
import { getGreeting } from './utils.ts';

// ... Worker logic ...

A bundler will take src/worker.ts as an entry point, resolve the import, transpile any TypeScript, and combine everything into one JavaScript file.

After bundling, your Deno code, now transpiled to JavaScript and combined into a single file, looks like a standard Cloudflare Worker. This is the file you'd deploy.

Here's a simplified example of what the output might resemble, including our greeting logic:

Once your Deno code is transpiled and bundled into a single JavaScript file (e.g., worker.js), you can deploy it using Cloudflare's Wrangler CLI, just like any other Worker.

• Wrangler handles uploading this bundled file to Cloudflare.
• The Cloudflare edge network then runs your JavaScript, effectively executing your Deno-originating logic.

The developer experience is Deno-first, but the deployment target is a standard Worker.

When deploying Deno code to Cloudflare Workers, which two processes are essential to make your Deno modules compatible with the Worker runtime?

Great job! You've learned how Deno modules can be deployed as Cloudflare Workers.

• Cloudflare Workers run JavaScript, so Deno code needs transpilation (e.g., TypeScript to JavaScript).
• For efficient deployment, multiple Deno modules are combined into a single file through bundling.
• Tools like esbuild automate this, turning your Deno project into a standard Worker script.

This allows you to leverage Deno's ecosystem for development while benefiting from the global reach of Cloudflare Workers.