JavaScript Document prerenderingchange Event

function initAnalytics() {
  console.log("Analytics initialized");
}

if (document.prerendering) {
  document.addEventListener("prerenderingchange", initAnalytics, {
    once: true,
  });
  console.log("Waiting for prerenderingchange...");
} else {
  initAnalytics();
}

if (document.prerendering) {
  document.addEventListener(
    "prerenderingchange",
    () => {
      console.log("Prerender activated after this script ran");
    },

    { once: true },
  );
} else if (
  performance.getEntriesByType("navigation")[0]?.activationStart > 0
) {
  console.log("Prerender activated before this script ran");
} else {
  console.log("This page load was not via prerendering");
}

function whenActivated(fn) {
  if ("prerendering" in document && document.prerendering) {
    document.addEventListener("prerenderingchange", fn, { once: true });
  } else {
    fn();
  }
}

whenActivated(() => {
  console.log("Safe to start analytics / ads now");
});