The Page Visibility API allows developers to run specific code whenever the page user is on goes in focus or out of foucs. Imagine you run a game-hosting site and want to pause the game whenever the user loses focus on your tab. This is the way to go!
function pageChanged() { if (document.hidden) { console.log('User is on some other tab/out of focus') // line #1 } else { console.log('Hurray! User returned') // line #2 }}document.addEventListener("visibilitychange", pageChanged);
We're adding an event listener to the document; it fires whenever the page is changed. Sure, the pageChanged function gets an event object as well in the argument, but we can simply use the document.hidden property, ...
