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