1 files changed, 70 insertions, 0 deletions
diff --git a/web_src/js/markup/anchors.js b/web_src/js/markup/anchors.js
new file mode 100644
index 0000000..0e2c927
--- /dev/null
+++ b/web_src/js/markup/anchors.js
@@ -0,0 +1,70 @@
+import {svg} from '../svg.js';
+
+const addPrefix = (str) => `user-content-${str}`;
+const removePrefix = (str) => str.replace(/^user-content-/, '');
+const hasPrefix = (str) => str.startsWith('user-content-');
+
+// scroll to anchor while respecting the `user-content` prefix that exists on the target
+function scrollToAnchor(encodedId) {
+  if (!encodedId) return;
+  const id = decodeURIComponent(encodedId);
+  const prefixedId = addPrefix(id);
+  let el = document.getElementById(prefixedId);
+
+  // check for matching user-generated `a[name]`
+  if (!el) {
+    const nameAnchors = document.getElementsByName(prefixedId);
+    if (nameAnchors.length) {
+      el = nameAnchors[0];
+    }
+  }
+
+  // compat for links with old 'user-content-' prefixed hashes
+  if (!el && hasPrefix(id)) {
+    return document.getElementById(id)?.scrollIntoView();
+  }
+
+  el?.scrollIntoView();
+}
+
+export function initMarkupAnchors() {
+  const markupEls = document.querySelectorAll('.markup');
+  if (!markupEls.length) return;
+
+  for (const markupEl of markupEls) {
+    // create link icons for markup headings, the resulting link href will remove `user-content-`
+    for (const heading of markupEl.querySelectorAll('h1, h2, h3, h4, h5, h6')) {
+      const a = document.createElement('a');
+      a.classList.add('anchor');
+      a.setAttribute('href', `#${encodeURIComponent(removePrefix(heading.id))}`);
+      a.innerHTML = svg('octicon-link');
+      heading.prepend(a);
+    }
+
+    // remove `user-content-` prefix from links so they don't show in url bar when clicked
+    for (const a of markupEl.querySelectorAll('a[href^="#"]')) {
+      const href = a.getAttribute('href');
+      if (!href.startsWith('#user-content-')) continue;
+      a.setAttribute('href', `#${removePrefix(href.substring(1))}`);
+    }
+
+    // add `user-content-` prefix to user-generated `a[name]` link targets
+    // TODO: this prefix should be added in backend instead
+    for (const a of markupEl.querySelectorAll('a[name]')) {
+      const name = a.getAttribute('name');
+      if (!name) continue;
+      a.setAttribute('name', addPrefix(a.name));
+    }
+
+    for (const a of markupEl.querySelectorAll('a[href^="#"]')) {
+      a.addEventListener('click', (e) => {
+        scrollToAnchor(e.currentTarget.getAttribute('href')?.substring(1));
+      });
+    }
+  }
+
+  // scroll to anchor unless the browser has already scrolled somewhere during page load
+  if (!document.querySelector(':target')) {
+    scrollToAnchor(window.location.hash?.substring(1));
+  }
+}