Service Worker + Lighthouse Issue Demo

Lighthouse includes two audits which are used to determine if your Progressive Web App (PWA) works offline. There are the Current page responds with a 200 when offline and start_url responds with a 200 when offline audits. However, I'm getting a false positive for these audits when using Lighthouse 5.1.0 and a very simple service worker setup. This repo is intended to demonstrate this issue.

This repo contains a tiny service worker that just overrides the default fetch behaviour, in order to just call fetch:

self.addEventListener('fetch', (event) => {
    event.respondWith(fetch(event.request))
})

It doesn't cache anything. With this service worker, this PWA does not work offline. If you go offline and refresh the page, the page will fail to load. However, the offline audits in Lighthouse show that this page does work offline, which is incorrect.

Setup

// Install dependencies
npm i

// Start the express server
node index.js

To reproduce the issue

• Start the express server
• Navigate to localhost:3000
• Use the Audit panel in Chrome Dev Tools or the Lighthouse Chrome Extension to run Lighthouse
• Review the results - the Current page responds with a 200 when offline and start_url responds with a 200 when offline audits have passed