Make tasklist checkboxes clickable (#15791)

Co-authored-by: silverwind <me@silverwind.io>
Co-authored-by: Lauris BH <lauris@nix.lv>

web_src/js/markup/content.js

@@ -1,5 +1,12 @@
 import {renderMermaid} from './mermaid.js';
+import {initMarkupTasklist} from './tasklist.js';
 
-export async function renderMarkupContent() {
+// code that runs for all markup content
+export async function initMarkupContent() {
   await renderMermaid(document.querySelectorAll('code.language-mermaid'));
 }
+
+// code that only runs for comments
+export function initCommentContent() {
+  initMarkupTasklist();
+}

web_src/js/markup/tasklist.js

@@ -0,0 +1,62 @@
+/**
+ * Attaches `input` handlers to markdown rendered tasklist checkboxes in comments.
+ *
+ * When a checkbox value changes, the corresponding [ ] or [x] in the markdown string
+ * is set accordingly and sent to the server. On success it updates the raw-content on
+ * error it resets the checkbox to its original value.
+ */
+
+const preventListener = (e) => e.preventDefault();
+
+export function initMarkupTasklist() {
+  for (const el of document.querySelectorAll(`.markup[data-can-edit=true]`) || []) {
+    const container = el.parentNode;
+    const checkboxes = el.querySelectorAll(`.task-list-item input[type=checkbox]`);
+
+    for (const checkbox of checkboxes) {
+      if (checkbox.dataset.editable) return;
+      checkbox.dataset.editable = 'true';
+      checkbox.addEventListener('input', async () => {
+        const checkboxCharacter = checkbox.checked ? 'x' : ' ';
+        const position = parseInt(checkbox.dataset.sourcePosition) + 1;
+
+        const rawContent = container.querySelector('.raw-content');
+        const oldContent = rawContent.textContent;
+        const newContent = oldContent.substring(0, position) + checkboxCharacter + oldContent.substring(position + 1);
+        if (newContent === oldContent) return;
+
+        // Prevent further inputs until the request is done. This does not use the
+        // `disabled` attribute because it causes the border to flash on click.
+        for (const checkbox of checkboxes) {
+          checkbox.addEventListener('click', preventListener);
+        }
+
+        try {
+          const editContentZone = container.querySelector('.edit-content-zone');
+          const {updateUrl, context} = editContentZone.dataset;
+
+          await $.post(updateUrl, {
+            _csrf: window.config.csrf,
+            content: newContent,
+            context,
+          });
+
+          rawContent.textContent = newContent;
+        } catch (err) {
+          checkbox.checked = !checkbox.checked;
+          console.error(err);
+        }
+
+        // Enable input on checkboxes again
+        for (const checkbox of checkboxes) {
+          checkbox.removeEventListener('click', preventListener);
+        }
+      });
+    }
+
+    // Enable the checkboxes as they are initially disabled by the markdown renderer
+    for (const checkbox of checkboxes) {
+      checkbox.disabled = false;
+    }
+  }
+}