the only way to know about other tabs is if your tab spawned them. As the opener it could receive messages back from other tabs. (see postMessage: https://developer.mozilla.org/en-US/docs/Web/API/Window/postMessage ) There are some response headers that would also control what an opener could do with that tab handle. (such as "Cross-Origin-Opener-Policy": https://developer.mozilla.org/en-US/docs/Web/HTTP/Reference/Headers/Cross-Origin-Opener-Policy ) For instance, navigating away from initial URL.