1// Using requestIdleCallback for scheduling low-priority background tasks
2const idleCallback = () => {
3  // Perform background tasks
4  console.log('Background task executed');
5};
6
7window.requestIdleCallback(idleCallback);

1.button {
2  border: 0;
3  padding: 10px;
4  box-shadow:
5    -2px -2px 5px gray,
6    2px 2px 5px gray;
7}
8
9@media (forced-colors: active) {
10  .button {
11    /* Use a border instead, since box-shadow is forced to 'none' in forced-colors mode */
12    border: 2px ButtonText solid;
13  }
14}

1```
2const observer = new PerformanceObserver((list) => {
3  const entries = list.getEntries();
4  entries.forEach(entry => {
5    console.log(`Resource timing for ${entry.name}: ${entry.duration}ms`);
6  });
7});
8
9observer.observe({ entryTypes: ['resource'] });
10```

1// Using navigator.sendBeacon for sending data in the background
2const data = "Analytics data";
3navigator.sendBeacon("/analytics", data);
4
5// Sending analytics at the end of a session
6document.addEventListener("visibilitychange", function logData() {
7  if (document.visibilityState === "hidden") {
8    navigator.sendBeacon("/analytics", data);
9  }
10});

1const target = { value: 42 };
2const { proxy, revoke } = Proxy.revocable(target, {});
3
4console.log(proxy.value); // Output: 42
5revoke();
6console.log(proxy.value); // Throws TypeError: Cannot perform 'get' on a proxy that has been revoked