fix(flexsearch): enhance match highlighting and safe DOM manipulation (#903)

- Replaced the highlightMatches function with appendHighlightedText to improve match highlighting using safe text nodes.
- Updated DOM manipulation for search results to create elements directly instead of using innerHTML, enhancing security and performance.
- Ensured consistent handling of empty text and query cases in the new highlighting function.

assets/js/flexsearch.js

@@ -392,18 +392,36 @@ document.addEventListener("DOMContentLoaded", function () {
       return;
     }
 
-    // Highlight the query in the result text.
-    function highlightMatches(text, query) {
-      const escapedQuery = query.replace(/[-\\^$*+?.()|[\]{}]/g, '\\$&');
-      const regex = new RegExp(escapedQuery, 'gi');
-      return text.replace(regex, (match) => `<span class="hextra-search-match">${match}</span>`);
+    // Append text with highlighted matches using safe text nodes.
+    function appendHighlightedText(container, text, query) {
+      if (!text) return;
+      if (!query) {
+        container.textContent = text;
+        return;
       }
 
-    // Create a DOM element from the HTML string.
-    function createElement(str) {
-      const div = document.createElement('div');
-      div.innerHTML = str.trim();
-      return div.firstChild;
+      const escapedQuery = query.replace(/[-\\^$*+?.()|[\]{}]/g, '\\$&');
+      if (!escapedQuery) {
+        container.textContent = text;
+        return;
+      }
+
+      const regex = new RegExp(escapedQuery, 'gi');
+      let lastIndex = 0;
+      let match;
+      while ((match = regex.exec(text)) !== null) {
+        if (match.index > lastIndex) {
+          container.appendChild(document.createTextNode(text.slice(lastIndex, match.index)));
+        }
+        const span = document.createElement('span');
+        span.className = 'hextra-search-match';
+        span.textContent = match[0];
+        container.appendChild(span);
+        lastIndex = match.index + match[0].length;
+      }
+      if (lastIndex < text.length) {
+        container.appendChild(document.createTextNode(text.slice(lastIndex)));
+      }
     }
 
     function handleMouseMove(e) {
@@ -421,20 +439,35 @@ document.addEventListener("DOMContentLoaded", function () {
     for (let i = 0; i < results.length; i++) {
       const result = results[i];
       if (result.prefix) {
-        fragment.appendChild(createElement(`
-          <div class="hextra-search-prefix">${result.prefix}</div>`));
+        const prefix = document.createElement('div');
+        prefix.className = 'hextra-search-prefix';
+        prefix.textContent = result.prefix;
+        fragment.appendChild(prefix);
       }
-        let li = createElement(`
-        <li>
-          <a data-index="${i}" href="${result.route}" class=${i === 0 ? "hextra-search-active" : ""}>
-            <div class="hextra-search-title">`+ highlightMatches(result.children.title, query) + `</div>` +
-        (result.children.content ?
-            `<div class="hextra-search-excerpt">` + highlightMatches(result.children.content, query) + `</div>` : '') + `
-          </a>
-        </li>`);
+      const li = document.createElement('li');
+      const link = document.createElement('a');
+      link.dataset.index = i;
+      link.href = result.route;
+      if (i === 0) {
+        link.classList.add('hextra-search-active');
+      }
+
+      const title = document.createElement('div');
+      title.className = 'hextra-search-title';
+      appendHighlightedText(title, result.children.title, query);
+      link.appendChild(title);
+
+      if (result.children.content) {
+        const excerpt = document.createElement('div');
+        excerpt.className = 'hextra-search-excerpt';
+        appendHighlightedText(excerpt, result.children.content, query);
+        link.appendChild(excerpt);
+      }
+
+      li.appendChild(link);
       li.addEventListener('mousemove', handleMouseMove);
       li.addEventListener('keydown', handleKeyDown);
-      li.querySelector('a').addEventListener('click', finishSearch);
+      link.addEventListener('click', finishSearch);
       fragment.appendChild(li);
     }
     resultsElement.appendChild(fragment);