syncImages2.js

async function preCacheBookImage(book) {
  let smallImage = book.smallImage;
  if (!smallImage) return;

  let cachedImage = await caches.match(smallImage);
  if (cachedImage) return;

  if (/https:\/\/s3.amazonaws.com\/my-library-cover-uploads/.test(smallImage)) {
    let cache = await caches.open("local-images1");
    let img = await fetch(smallImage, { mode: "no-cors" });
    await cache.put(smallImage, img);
  }
}