The ETCSL website sometimes loses track of the selected encoding. This script fixes it and makes switching between Unicode and ASCII easy.

etcsl_charenc_fix.user.js

// ==UserScript==
// @name        ETCSL charenc fix
// @namespace   https://github.com/vyznev/
// @description The ETCSL website sometimes loses track of the selected encoding. This script fixes it and makes switching between Unicode and ASCII easy.
// @author      Ilmari Karonen
// @version     1.1
// @match       *://etcsl.orinst.ox.ac.uk/*
// @homepageURL https://gist.github.com/vyznev/b078af6b3574f80879f93675f59d8c86
// @downloadURL https://gist.github.com/vyznev/b078af6b3574f80879f93675f59d8c86/raw/etcsl_charenc_fix.user.js
// @run-at      document-start
// @grant       none
// ==/UserScript==

(function () {
  const scriptURL = new URL('https://etcsl.orinst.ox.ac.uk/cgi-bin/etcsl.cgi');

  // If the URL has no explicit charenc parameter, use charenc=gcirc (Unicode)
  const locURL = new URL(location);
  if (locURL.pathname === scriptURL.pathname && locURL.search && !locURL.searchParams.get('charenc')) {
    locURL.searchParams.set('charenc', 'gcirc');
    console.log(`ETCSL charenc fix rewriting location ${location} to ${locURL}`)
    return location.replace(locURL);
  }

  function domFixes () {
    // If it does, but some links on the page don't, fix them
    const charenc = locURL.searchParams.get('charenc') || 'gcirc';
    const links = document.querySelectorAll('a[href]');
    for (const link of links) {
      const url = new URL(link.href, location);
      if (url.host === scriptURL.host && url.pathname === scriptURL.pathname && !url.searchParams.get('charenc')) {
        url.searchParams.set('charenc', charenc);
        console.log(`ETCSL charenc fix rewriting link ${link.href} to ${url}`)
        link.href = url;
      }
    }

    // Inject links for switching between Unicode and ASCII encodings
    const subtitle = document.querySelector('body > hr + h2');
    if (subtitle && locURL.pathname === scriptURL.pathname) {
      function makeLink(enc, label) {
        const url = new URL(location);
        let link = document.createElement('b');
        if (url.searchParams.get('charenc') !== enc) {
      	  url.searchParams.set('charenc', enc);
          link = document.createElement('a');
          link.href = url;
        }
        link.append(label);
        return link;
      }
      const wrapper = document.createElement('div');
      wrapper.append('Select encoding: ');
      wrapper.append(makeLink('gcirc', 'Unicode'));
      wrapper.append(' | ');
      wrapper.append(makeLink('j', 'Ascii'));
      wrapper.style = 'float: right';
      console.log(`ETCSL charenc fix injecting`, wrapper);
      subtitle.parentNode.insertBefore(wrapper, subtitle);
    }
  }

  if (document.readyState !== 'loading') {
    domFixes();
  } else {
    window.addEventListener('DOMContentLoaded', domFixes);
  }
})();