async function handleEvent(event) {
  const url = new URL(event.request.url)
  let options = {}

  /**
   * You can add custom logic to how we fetch your assets
   * by configuring the function `mapRequestToAsset`
   */
  // options.mapRequestToAsset = handlePrefix(/^\/docs/)

  try {
    if (DEBUG) {
      // customize caching
      options.cacheControl = {
        bypassCache: true,
      }
    }
    return await getAssetFromKV(event, options)
  } catch (e) {
    // if an error is thrown try to serve the asset at 404.html
    if (!DEBUG) {
      try {
        let notFoundResponse = await getAssetFromKV(event, {
          mapRequestToAsset: req => new Request(`${new URL(req.url).origin}/404.html`, req),
        })

        return new Response(notFoundResponse.body, { ...notFoundResponse, status: 404 })
      } catch (e) {}
    }

    return new Response(e.message || e.toString(), { status: 500 })
  }
}
The DEBUG flag will do two things that help during development:
1. we will skip caching on the edge, which makes it easier to
   debug.
2. we will return an error message on exception in your Response rather
   than the default 404.html page.