Most developers find this API by accident — usually while chasing a bug where the user logged out in one tab and the other three still show the dashboard. Embarrassing in dev, security issue in prod.
The fix is built into every modern browser. It's called BroadcastChannel. Most people skip it because they didn't know it was there.
What even is it?
You know how your browser can have the same website open in multiple tabs? Those tabs are completely isolated from each other — they can't talk. Open five tabs of your app and each one lives in its own little bubble.
The BroadcastChannel API fixes that. It lets any tab, window, or iframe on the same origin send a message to all the others. One line to open a channel, one line to send, one line to listen. That's it.
