The read-only XRSessionEvent interface's session property indicates which XRSession the event is about.

An XRSession object indicating which WebXR session the event refers to.

In this example, the session property is used to obtain the session object to manage when an event is received.

xrSession.addEventListener("visibilitychange", (e) => {
  switch (e.session.visibilityState) {
    case "hidden":
      myEnableRendering(true);
      break;
    case "visible":
    case "visible-blurred":
      myEnableRendering(false);
      break;
  }
});

This calls a function that reacts to the session's visibility state change.