PERF: attempts to resort to compute markdown in less cases (#15762)

app/assets/javascripts/discourse/app/components/quote-button.js

@@ -5,6 +5,7 @@ import { popupAjaxError } from "discourse/lib/ajax-error";
 import {
   postUrl,
   selectedElement,
+  selectedRange,
   selectedText,
   setCaretPosition,
   translateModKey,
@@ -164,10 +165,14 @@ export default Component.extend(KeyEnterEscape, {
     const cooked =
       $selectedElement.find(".cooked")[0] ||
       $selectedElement.closest(".cooked")[0];
-    const postBody = toMarkdown(cooked.innerHTML);
 
+    // computing markdown takes a lot of time on long posts
+    // this code attempts to compute it only when we can't fast track
     let opts = {
-      full: _selectedText === postBody,
+      full:
+        selectedRange().startOffset > 0
+          ? false
+          : _selectedText === toMarkdown(cooked.innerHTML),
     };
 
     for (

app/assets/javascripts/discourse/app/lib/utilities.js

@@ -207,9 +207,13 @@ export function selectedText() {
 }
 
 export function selectedElement() {
+  return selectedRange()?.commonAncestorContainer;
+}
+
+export function selectedRange() {
   const selection = window.getSelection();
   if (selection.rangeCount > 0) {
-    return selection.getRangeAt(0).commonAncestorContainer;
+    return selection.getRangeAt(0);
   }
 }