get url after "#" in express.js middleware request

Any path/query param after # (Hash symbol) in URL will be removed by the browser.

This can be handled by a small hack by replacing the hash with an EMPTY string in the script tag of HTML/EJS file which will remove the hash and the entire URL will be passed to the server.

In case of a server side rendered application, applying the above technique in the 404 will route the redirection back to the valid router.

<script>
  const hash = window.location.hash;
  if(hash.length > 0 && hash.includes("#/")) {
    window.location.replace(window.location.href.replace('#/',''));
  }
</script>

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This worked well in my application. Thanks to my teammates for this fix.

No. The part of the URL starting with the # symbol is never sent to the server.

The # symbol in an URL is to introduce the fragment identifier. This is used to link to a specific part of the page. If a browser loads /#some/url, it will effectively load /, and skip to the HTML element with id="some/url" (if present). The fragment identifier is only relevant to the browser, so it is not sent with the HTTP request.

What you however can do, is using client side Javascript to read out the value of window.location.hash and send it to the server using an XMLHttpRequest. (See other Stack Overflow post.)