// @author Josh Parker

one-page-category.meta.js

// ==UserScript==
// @name         Show all category links on one page.
// @namespace    http://tampermonkey.net/
// @version      0.1
// @description
// @author       Josh Parker
// @source       https://github.com/joshparkerj/silly-internet-tricks/blob/main/wikipedia/one-page-category.user.js
// @downloadURL  https://gist.github.com/joshparkerj/3e8e7b624a12c4b4a9fcd3bb349be74f/raw/one-page-category.user.js
// @updateURL    https://gist.github.com/joshparkerj/3e8e7b624a12c4b4a9fcd3bb349be74f/raw/one-page-category.meta.js
// @match        https://en.wikipedia.org/wiki/Category:*
// @match        https://en.wikipedia.org/w/index.php?title=Category:*
// @icon         https://www.google.com/s2/favicons?domain=wikipedia.org
// @grant        none
// ==/UserScript==

one-page-category.user.js

// ==UserScript==
// @name         Show all category links on one page.
// @namespace    http://tampermonkey.net/
// @version      0.1
// @description
// @author       Josh Parker
// @source       https://github.com/joshparkerj/silly-internet-tricks/blob/main/wikipedia/one-page-category.user.js
// @downloadURL  https://gist.github.com/joshparkerj/3e8e7b624a12c4b4a9fcd3bb349be74f/raw/one-page-category.user.js
// @updateURL    https://gist.github.com/joshparkerj/3e8e7b624a12c4b4a9fcd3bb349be74f/raw/one-page-category.meta.js
// @match        https://en.wikipedia.org/wiki/Category:*
// @match        https://en.wikipedia.org/w/index.php?title=Category:*
// @icon         https://www.google.com/s2/favicons?domain=wikipedia.org
// @grant        none
// ==/UserScript==
!function(){let e=document.querySelector("div#mw-pages > div.mw-content-ltr");if(!e){const t=document.createElement("div");t.id="mw-pages",e=document.createElement("div"),e.classList.add("mw-content-ltr"),t.appendChild(e),document.querySelector("div#mw-content-text").after(t)}const t=document.querySelector("div#mw-pages"),n=[...t.childNodes].filter((e=>"A"===e.tagName)),r=n.filter((e=>e.textContent.includes("next"))),l=n.filter((e=>e.textContent.includes("previous"))),i=r.length>0?r[0].href:null,c=l.length>0?l[0].href:null,o=new DOMParser,d=function t(n,r){n&&fetch(n).then((e=>e.text())).then((e=>o.parseFromString(e,"text/html"))).then((n=>{const l=[...n.querySelectorAll("#mw-pages > a")].filter((e=>e.textContent.includes(r))),i=l.length>0?l[0].href:null,c=n.querySelector("#mw-pages > .mw-content-ltr").innerHTML;"next"===r?e.innerHTML+=`<hr>${c}`:"previous"===r&&(e.innerHTML=`${c}<hr>${e.innerHTML}`),t(i,r)}))},s=document.createElement("button");s.innerText="show all",s.addEventListener("click",(()=>{s.setAttribute("disabled",!0),d(i,"next"),d(c,"previous")})),(i||c)&&t.appendChild(s)}();

wikipedia-one-page-category.user.js

// ==UserScript==
// @name         Show all category links on one page.
// @namespace    http://tampermonkey.net/
// @version      0.1
// @description
// @author       Josh Parker
// @match        https://en.wikipedia.org/wiki/Category:*
// @match        https://en.wikipedia.org/w/index.php?title=Category:*
// @icon         https://www.google.com/s2/favicons?domain=wikipedia.org
// @grant        none
// ==/UserScript==

(function categoryOnePageUserScript() {
  let categoryArea = document.querySelector('div#mw-pages > div.mw-content-ltr');
  if (!categoryArea) {
    const mwPages = document.createElement('div');
    mwPages.id = 'mw-pages';
    categoryArea = document.createElement('div');
    categoryArea.classList.add('mw-content-ltr');
    mwPages.appendChild(categoryArea);
    document.querySelector('div#mw-content-text').after(mwPages);
  }

  const categoryPages = document.querySelector('div#mw-pages');
  const navLinks = [...categoryPages.childNodes].filter((node) => node.tagName === 'A');
  const nextLinks = navLinks.filter((a) => a.textContent.includes('next'));
  const previousLinks = navLinks.filter((a) => a.textContent.includes('previous'));
  const nextHref = nextLinks.length > 0 ? nextLinks[0].href : null;
  const previousHref = previousLinks.length > 0 ? previousLinks[0].href : null;
  const parser = new DOMParser();
  const getMorePages = function getMorePages(href, direction) {
    if (!href) {
      return;
    }

    fetch(href)
      .then((r) => r.text())
      .then((text) => parser.parseFromString(text, 'text/html'))
      .then((doc) => {
        const docLinks = [...doc.querySelectorAll('#mw-pages > a')].filter((a) => a.textContent.includes(direction));
        const docHref = docLinks.length > 0 ? docLinks[0].href : null;
        const docCategoryArea = doc.querySelector('#mw-pages > .mw-content-ltr').innerHTML;
        if (direction === 'next') {
          categoryArea.innerHTML += `<hr>${docCategoryArea}`;
        } else if (direction === 'previous') {
          categoryArea.innerHTML = `${docCategoryArea}<hr>${categoryArea.innerHTML}`;
        }

        getMorePages(docHref, direction);
      });
  };

  const getAllLaterPages = (href) => getMorePages(href, 'next');
  const getAllEarlierPages = (href) => getMorePages(href, 'previous');

  const showAllButton = document.createElement('button');
  showAllButton.innerText = 'show all';
  showAllButton.addEventListener('click', () => {
    showAllButton.setAttribute('disabled', true);
    getAllLaterPages(nextHref);
    getAllEarlierPages(previousHref);
  });

  if (nextHref || previousHref) {
    categoryPages.appendChild(showAllButton);
  }
}());