oak-gpui/docs/theme/page-toc.js

let scrollTimeout;

const listenActive = () => {
  const elems = document.querySelector(".pagetoc").children;
  [...elems].forEach((el) => {
    el.addEventListener("click", (event) => {
      clearTimeout(scrollTimeout);
      [...elems].forEach((el) => el.classList.remove("active"));
      el.classList.add("active");
      // Prevent scroll updates for a short period
      scrollTimeout = setTimeout(() => {
        scrollTimeout = null;
      }, 100); // Adjust timing as needed
    });
  });
};

const getPagetoc = () =>
  document.querySelector(".pagetoc") || autoCreatePagetoc();

const autoCreatePagetoc = () => {
  const main = document.querySelector("#content > main");
  const content = Object.assign(document.createElement("div"), {
    className: "content-wrap",
  });
  content.append(...main.childNodes);
  main.prepend(content);
  main.insertAdjacentHTML(
    "afterbegin",
    '<div class="sidetoc"><nav class="pagetoc"></nav></div>',
  );
  return document.querySelector(".pagetoc");
};
const updateFunction = () => {
  if (scrollTimeout) return; // Skip updates if within the cooldown period from a click
  const headers = [...document.getElementsByClassName("header")];
  const scrolledY = window.scrollY;
  let lastHeader = null;

  // Find the last header that is above the current scroll position
  for (let i = headers.length - 1; i >= 0; i--) {
    if (scrolledY >= headers[i].offsetTop) {
      lastHeader = headers[i];
      break;
    }
  }

  const pagetocLinks = [...document.querySelector(".pagetoc").children];
  pagetocLinks.forEach((link) => link.classList.remove("active"));

  if (lastHeader) {
    const activeLink = pagetocLinks.find(
      (link) => lastHeader.href === link.href,
    );
    if (activeLink) activeLink.classList.add("active");
  }
};

window.addEventListener("load", () => {
  const pagetoc = getPagetoc();
  const headers = [...document.getElementsByClassName("header")];

  const nonH1Headers = headers.filter(
    (header) => !header.parentElement.tagName.toLowerCase().startsWith("h1"),
  );
  const sidetoc = document.querySelector(".sidetoc");
  const tocContainer = document.querySelector(".toc-container");

  if (nonH1Headers.length === 0) {
    if (sidetoc) {
      sidetoc.style.display = "none";
    }
    if (tocContainer) {
      tocContainer.style.display = "none";
    }
    return;
  }

  headers.forEach((header) => {
    const link = Object.assign(document.createElement("a"), {
      textContent: header.text,
      href: header.href,
      className: `pagetoc-${header.parentElement.tagName}`,
    });
    pagetoc.appendChild(link);
  });
  updateFunction();
  listenActive();
  window.addEventListener("scroll", updateFunction);
});