title: How to inject javascript in existing HTML response with node.js and cloudflare workers
body: <p>I have a vanity URL pointing to a GitBook. GitBook doesn't support the insertion of arbitrary javascript snippets. At the moment GitBook has 4 "integrations" only. </p>
  
  <p>I could route through my own VM server to accomplish this, but I have CloudFlare and I want to try out workers. (Javascript running at the CDN edge).</p>
  
  <p>The CloudFlare worker environment makes header injection very easy, but there is no obvious way to do this.</p>