proxygist.js

const BASE_DOMAIN = ""

addEventListener('fetch', function (event) {
  const { request } = event
  const response = handleRequest(request).catch(handleError)
  event.respondWith(response)
})

/**
 * Receives a HTTP request and replies with a response.
 * @param {Request} request
 * @returns {Promise<Response>}
 */
async function handleRequest(request) {
  const { method, url } = request
  const { host, pathname } = new URL(url)
  let matchStatus = -1

  // https://gist.github.com/BexTuychiev/ad0b1318a392691a74666fd34171afb2.js
  const reMatchJS = /\/(.*)\/(.*).js$/

  // https://github.githubassets.com/assets/gist-embed-ceaaa09008a5bc2758b9ee6a1c99082d.css
  const reMatchCssAssets = /\/assets\/(.*)/


  if(reMatchJS.test(pathname)) matchStatus = 1;

  if(reMatchCssAssets.test(pathname)) matchStatus = 2;

  console.log(pathname, matchStatus, reMatchJS.test(pathname))

  switch (matchStatus) {
    case 1:
      return await proxyJS(pathname);
    case 2:
      return await proxyCSS(pathname);
    default:
      return new Response(`Not match path ${pathname}. \nPlease check it`, {status: 409})
  }
}


async function proxyJS(pathname) {
  console.log('proxy js')

  const base = "https://gist.github.com"
  return await fetchContent(base, pathname, true, 'github.githubassets.com', BASE_DOMAIN)

}

async function proxyCSS(pathname) {
  console.log('proxy css')

  const base = "https://github.githubassets.com"

  return await fetchContent(base, pathname)

}

async function fetchContent(base, pathname, isReplace = false, re, reContent) {
  const url = base + pathname
  const myRequest = new Request(url)
  const proxyData = await fetch(myRequest)
  const { status, statusText, body} = proxyData
  if(status != 200) return new Response('Error From Github: ' + statusText, {status: status})
  
  if(isReplace) {
    let originText = await proxyData.text()
    originText = originText.replace(re,reContent);
    return new Response(originText, {status: 200})
  } else {
    return new Response(body, {status: 200})
  }

}