Active / Offline state of browser tab

<script> 
document.addEventListener("visibilitychange", function() {
      document.title = document.hidden ? "I'm away" : "I'm here";
});
document.addEventListener("visibilitychange", (event) => {
  if (document.visibilityState == "visible") {
    console.log("tab is active")
  } else {
    console.log("tab is inactive")
  }
}); 

var siteTitle="";
window.addEventListener('blur', () => {
  siteTitle = document.title;
  document.title = 'Come back! :c';
});
window.addEventListener('focus', () => {
  document.title = siteTitle;
});
</script>