How to prevent subrequests when fetching external data

I note that each time I make a GET/POST request to fetch external data in a Worker, two requests are made. An initial request, quickly followed by a subrequest immediately after.

The issue is that I’m making an external API request to trigger document generation and I don’t want to make a duplicate request. Is there any way to avoid this?

Oddly enough, I note that a subrequest is only made when loading the URL in a user agent (I’m using a web browser). That is, if I open make the request from the web interface (below), only a single request is made.

Here’s some code to reproduce this behavior:

const baseUrl = ''
const url = baseUrl + 'G9O31lm1LqcWGGeQq13l'

async function gatherResponse(response) {
    return await response.text()

async function handleRequest() {

  const init = {
  headers: {
    'Content-Type': 'application/json'

  const responses = await Promise.all([
    await fetch(url, init)
    // will add others here

  const results = await Promise.all([
  return new Response(results.join(), init)

addEventListener('fetch', event => {
  return event.respondWith(handleRequest())

The browser when fetches with a GET, runs a fetch OPTIONS before.
You will see two requests at least.
Another is the browser always requesting /favicon.ico

You could limit verbs (methods) with a condition:
if (["GET", "POST"].includes(request.method))

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