JavaScript Document hidden Property

console.log(document.hidden);
// false while you are looking at this tab

document.addEventListener("visibilitychange", () => {
  console.log(document.hidden);
  // Modify behavior…
});

let ticks = 0;
let timer = null;

function start() {
  if (timer) return;
  timer = setInterval(() => {
    ticks += 1;
    console.log("tick", ticks);
  }, 1000);
}

function stop() {
  clearInterval(timer);
  timer = null;
}

document.addEventListener("visibilitychange", () => {
  if (document.hidden) {
    stop();
  } else {
    start();
  }
});

if (!document.hidden) start();