Web APIs

Web APIs extend JavaScript with browser capabilities. Workers run in separate realms without direct DOM access and communicate using structured-clone messages and transferable objects.

Observe without polling

const observer = new IntersectionObserver(entries => {
  for (const entry of entries) {
    if (entry.isIntersecting) loadPreview(entry.target);
  }
});
observer.observe(document.querySelector("[data-preview]"));

MutationObserver reports DOM changes; ResizeObserver reports element size; WebSocket provides full-duplex messages; BroadcastChannel communicates same-origin contexts. Geolocation, notifications, media, clipboard, and other powerful APIs require secure contexts and permissions. Feature-detect, handle denial, clean up observers/connections, and bound incoming data.