Using JSR with Cloudflare Workers

Cloudflare Workers provides a serverless execution environment for JavaScript and WebAssembly that can execute your code on Cloudflare’s global network.

JSR packages can be used in Cloudflare Workers by using JSR’s npm compatibility layer.

First, create a new Cloudflare Worker project:

npm create cloudflare@latest
yarn create cloudflare
pnpm create cloudflare
bun create cloudflare

You can then add JSR packages using your package manager. This will add the package to your package.json and install it into your node_modules folder using your preferred package manager (npm, yarn, or pnpm).

# pnpm 10.9+ and yarn 4.9+
pnpm add jsr:@std/encoding
yarn add jsr:@std/encoding

# npm, bun, and older versions of yarn or pnpm
npx jsr add @std/encoding
bunx jsr add @std/encoding
yarn dlx jsr add @std/encoding
pnpm dlx jsr add @std/encoding

Note: A .npmrc file is created when using the JSR CLI. The .npmrc file that is created should be checked into source control. Without this, future calls to npm install / yarn / pnpm install / bun install will not succeed.

You can then import JSR packages in your code:

import { encodeBase64 } from "@std/encoding/base64";

export default {
  async fetch(request: Request): Promise<Response> {
    return new Response(encodeBase64("Hello World!"));
  },
};

Running wrangler dev to start the local development server will run your Cloudflare Worker. You can then visit http://localhost:8787 to see the result.

wrangler dev

Learn more about using packages.