I spent a week trying to intercept Slack push notifications from a Chrome extension. Here's why it's impossible.

After I published my last article about building a Chrome extension that speaks browser notifications aloud, a commenter asked a question I didn't have a good answer to.

He pointed out that a lot of web apps — Slack, Gmail, most modern tools — fire their notifications from a service worker via registration.showNotification(), not from the page's JavaScript context. My MAIN world override of window.Notification would never reach those.

He was right. And I told him I'd look into it.

I spent a week researching whether there was any way to close that gap. There isn't. But the reason why is more interesting than a simple "no."

Two ways a website can show you a notification