Cloudflare Workers #

A Cloudflare Workers is a JavaScript edge runtime on Cloudflare CDN.

You can develop the application locally and publish it with a few commands using Wrangler, a CLI developed by Cloudflare. Wrangler includes trans compiler, so we can write the code with TypeScript.

Let’s make your first application for Cloudflare Workers with Hono.

1. Install #

wrangler init #

Initialize the project with Wrangler.

mkdir hono-example
cd hono-example
npx wrangler init -y

npm install hono #

Install hono from the npm registry.

npm init -y
npm i hono

2. Hello World #

Edit src/index.ts:

// src/index.ts
import { Hono } from 'hono'
const app = new Hono()

app.get('/', (c) => c.text('Hello! Hono!'))

export default app

3. Run #

Run the development server locally. Then, access http://localhost:8787 in your Web browser.

npx wrangler dev

4. Publish #

If you have the Cloudflare account, you can deploy to Cloudflare.

npx wrangler publish ./src/index.ts

That’s all!

Starter template #

You can start making your Cloudflare Workers application with the starter template. It is really minimal using TypeScript, esbuild, Miniflare, and Jest.

To generate a project skeleton, run this command.

npx create-cloudflare my-app

Advanced #

Service Worker mode or Module Worker mode #

There are two syntax for writing the Cloudflare Workers. Service Worker mode and Module Worker mode. Using Hono, you can write with both syntax:

// Service Worker
// Module Worker
export default app

Now, we recommend using Module Worker mode because the binding variables are localized.

Types #

You have to install @cloudflare/workers-types if you want to have types.

npm i --save-dev @cloudflare/workers-types

Testing #

For testing, we recommend using jest-environment-miniflare. Refer to the starter template for setting it up.

If there is the application below:

import { Hono } from 'hono'

const app = new Hono()
app.get('/', (c) => c.text('Please test me!'))

We can test that it is returning “200 OK” Response with this code:

describe('Test the application', () => {
  it('Should return 200 response', async () => {
    const res = await app.request('http://localhost/')

Bindings #

In the Cloudflare Workers, we can bind the environment values, KV namespace, R2 bucket, or Durable Object. You can access them in c.env. It will have the types if you pass the “type struct” for the bindings to the Hono as generics.

interface Env {
  BUCKET: R2Bucket
  USER: string
  PASS: string

const app = new Hono<{ Bindings: Env }>()

// Access to environment values
app.put('/upload', async (c, next) => {
  const auth = basicAuth({ username: c.env.USER, password: c.env.PASS })
  await auth(c, next)
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