web

prefetch.js

function prefetch(nodeLists) {
  // Exclude slow ECTs < 3g
  if (
    navigator.connection &&
    (navigator.connection.effectiveType === "slow-2g" ||
      navigator.connection.effectiveType === "2g")
  ) {
    return;
  }

  // Exclude low end device which is device with memory <= 2GB
  if (navigator.deviceMemory && navigator.deviceMemory <= 2) {
    return;
  }

  const fetchLinkList = {};

  const observer = new IntersectionObserver(function (entries) {
    entries.forEach(function (entry) {
      if (entry.isIntersecting) {
        if (!fetchLinkList[entry.target.href]) {
          fetchLinkList[entry.target.href] = true;

          fetch(entry.target, {
            priority: "low",
          });
        }

        observer.unobserve((entry = entry.target));
      }
    });
  });
}

const idleCallback =
  window.requestIdleCallback ||
  function (cb) {
    let start = Date.now();

    return setTimeout(function () {
      cb({
        didTimeout: false,
        timeRemaining: function () {
          return Math.max(0, 50 - (Date.now() - start));
        },
      });
    }, 1);
  };

idleCallback(function () {
  prefetch(nodeLists);
});