//if this is the link, return false var tab = window.open("https://www.google.com.vn/", "_blank"); // if this is the link, reture true // var tab = window.open("https://www.google.com/search?q=coin&oq=coin&aqs=chrome..69i57j0i131i433i512j0i433i512l2j46i131i199i433i465i512j0i131i433i512j46i131i199i433i465i512j0i131i433i512j0i433i512j0i512.665j0j15&sourceid=chrome&ie=UTF-8", "_blank"); // I want to know why it is true and how to fix it setInterval(function() { checkTabsClosed() }, 3000); function checkTabsClosed() { console.log(tab); if (tab && tab.closed) { console.log("close"); } else console.log("open"); }