Redirect requests inside html page to go through proxy

I have a proxy, and I’ve fetched contents of the webpage I need, like https://google.com. However, I need to be able to then also redirect all the other requests for resources to go through the proxy. So, all images and scripts go back through the proxy. Additionally, all links also go back through the proxy. How can I access all of the requests and do this? Would this be through modifying the HTML of the site? Now, I should be able to serve the contents of any dynamic or static site on a localhost, without having certain elements and scripts not loading.

Answer

So I found the solution!

Using a service worker I can redirect requests to go back through the forward proxy. This example proxies requests from an old api version to a new one (this isn’t what Im doing though. It would add a certain url, like https://api.allorigins.win/get?url= to the beginning):

self.addEventListener('fetch', e => {
  const {url} = e.request;
  if(url.includes('https://api.your.domain/api/v1/') {
    const newUrl = url.replace('/api/v1/', '/api/v2/');
    e.respondWith(fetch(newUrl));
  }
});

This article essentially fixes my problem: https://betterprogramming.pub/how-to-run-a-proxy-server-inside-your-browser-8b96ea2ef1ea