gioboa / cloudflare-qwik-mfes

Small repro of Cloudflare Qwik MFEs to demonstrate the challenges we're facing

Cloudflare Qwik MFEs

This repository demonstrates the challenges we are facing using Qwik in a Cloudflare micro-frontend (MFE) architecture.

This is a scaled down version of an application using two MFEs - main and body. main is the entry point, and renders the body MFE inside of it. Upon serving the application, you'll notice dotted borders are used on container elements to clearly show the boundary between MFEs.

The main challenge is around prefetching where multiple Qwik containers are used. Containers emit a 'qprefetch' CustomEvent with filenames for their bundles, and a global listener forwards them to a Service Worker for prefetching. The problem is that the global listener uses document.currentScript.closest('[q\\:container]') to resolve the base, which will always resolve to main. This architecture works when a single container is used, but when there are multiple containers, each with a unique base, the listener fails to construct the correct URLs for bundles outside of main.

body renders a button to interact with. On click, this will render a new component to demonstrate lazy loading (and the lack of prefetching). All qprefetch events are logged to the console, which demonstrates that bundles are emitted without a base. In the HTML, the prefetch-service-worker script element shows the global listener, which clearly shows how the base is resolved.

In creating this reproduction another bug has been spotted with the Service Worker itself.

This function is taken from https://github.com/QwikDev/qwik/blob/f6fc2f855a11b541d383bf9b26db399dbb781a5a/packages/qwik/src/prefetch-service-worker/process-message.ts#L150

export function drainMsgQueue(swState: SWState) {
  if (!swState.$msgQueuePromise$ && swState.$msgQueue$.length) {
    const top = swState.$msgQueue$.shift()!;
    swState.$msgQueuePromise$ = processMessage(swState, top).then(() => {
      drainMsgQueue(swState);
    });
  }
}

Messages are only processed when $msgQueuePromise$ is falsey. Conceptually this is fine, however there is no code that restores it to a falsey value when all messages are processed. The result is that only the first message to the SW is processed.

Installing

This project uses NPM workspaces. Running npm i at the project root will install all dependencies for all MFEs.

Docs for main dependencies:

• Wrangler, used to serve the application in a local Cloudflare environment.
• Qwik, used to write the application.
• Vite, used to build the application.

Serving

Both MFEs need to be served to view the full application.

1. Open a terminal in the /packages/main directory, and run npm start.
2. Open a terminal in the /packages/body directory, and run npm start.

main will serve on localhost:8080, you can view the full application from here. body will serve inside main, but can be viewed in isolation on localhost:8080.