Debugging logs

// Service configured to receive logs
const LOG_URL = 'https://log-service.example.com/';

function postLog(data) {
  return fetch(LOG_URL, {
    method: 'POST',
    body: data,
  });
}

async function handleRequest(event) {
  let response;

  try {
    response = await fetch(event.request);
    if (!response.ok && !response.redirected) {
      const body = await response.text();
      throw new Error(
        'Bad response at origin. Status: ' +
          response.status +
          ' Body: ' +
          // Ensure the string is small enough to be a header
          body.trim().substring(0, 10)
      );
    }
  } catch (err) {
    // Without event.waitUntil(), your fetch() to Cloudflare's
    // logging service may or may not complete
    event.waitUntil(postLog(err.toString()));
    const stack = JSON.stringify(err.stack) || err;

    // Copy the response and initialize body to the stack trace
    response = new Response(stack, response);

    // Add the error stack into a header to find out what happened
    response.headers.set('X-Debug-stack', stack);
    response.headers.set('X-Debug-err', err);
  }
  return response;
}

addEventListener('fetch', event => {
  // Have any uncaught errors thrown go directly to origin
  event.passThroughOnException();
  event.respondWith(handleRequest(event));
});