Starting a Cloudflare Worker from scratch

While tooling for web development is getting more and more complex, with CLIs for your CLIs becoming a thing, sometimes it's worth taking a step back, and realizing that doing things from scratch isn't so hard.

In this article, we're going to create and deploy a Cloudflare Worker without a CLI.

Table of contents

• Steps to "Hello World"
• Summary

Steps to "Hello World"

1. Make a new directory, and cd into it

mkdir my-worker/
cd my-worker/

2. Initialize the npm project

npm init -y

3. Install some packages

npm install -D typescript wrangler @cloudflare/workers-types

4. Create a tsconfig.json file

touch tsconfig.json

After running the above command, paste the following into tsconfig.json:

//tsconfig.json
{
  "compilerOptions": {
    "noEmit": true,
    "module": "esnext",
    "target": "esnext",
    "lib": ["esnext"],
    "strict": true,
    "moduleResolution": "node",
    "types": ["@cloudflare/workers-types"]
  }
}

5. Make a src/ directory, create an index.ts file inside

mkdir src/
touch src/index.ts

After running the above command, paste the following into index.ts:

// index.ts
export default {
  fetch: () => {
    return new Response('Hello World!');
  },
};

6. Create a wrangler.toml file

touch wrangler.toml

After running the above command, paste the following into wrangler.toml:

# wrangler.toml
name = "my-worker"
main = "src/index.ts"
compatibility_date = "2023-12-22"

7. Login to wrangler

npx wrangler login

8. Deploy your Worker

npx wrangler deploy

You can now visit the URL that wrangler outputs, and you should see "Hello World" in your browser.

9. (optionally) Install vitest, add a test script

npm install vitest -D
touch src/index.test.ts

After running the above commands, paste the following into src/index.test.ts:

import { unstable_dev } from 'wrangler';
import type { UnstableDevWorker } from 'wrangler';
import { describe, expect, it, beforeAll, afterAll } from 'vitest';

describe('Worker', () => {
  let worker: UnstableDevWorker;

  beforeAll(async () => {
    worker = await unstable_dev('src/index.ts', {
      experimental: { disableExperimentalWarning: true },
    });
  });

  afterAll(async () => {
    await worker.stop();
  });

  it('should return Hello World', async () => {
    const resp = await worker.fetch();
    if (resp) {
      const text = await resp.text();
      expect(text).toMatchInlineSnapshot(`"Hello World!"`);
    }
  });
});

Finally, in package.json replace the test script with:

"test": "vitest"

Summary

There you have it, a Cloudflare Worker from scratch.

While it's not strictly better than just running

npx wrangler@2 init my-worker2 -y

(which is the exact CLI command you'd run to get the project above)

At least this way you understand what's happening before reaching for tooling to automate it.