Converted app/javascript/mastodon/utils/ folder to TypeScript (#27895)

app/javascript/mastodon/utils/scrollbar.ts

@@ -0,0 +1,31 @@
+import { isMobile } from '../is_mobile';
+
+let cachedScrollbarWidth: number | null = null;
+
+const getActualScrollbarWidth = () => {
+  const outer = document.createElement('div');
+  outer.style.visibility = 'hidden';
+  outer.style.overflow = 'scroll';
+  document.body.appendChild(outer);
+
+  const inner = document.createElement('div');
+  outer.appendChild(inner);
+
+  const scrollbarWidth = outer.offsetWidth - inner.offsetWidth;
+  outer.remove();
+
+  return scrollbarWidth;
+};
+
+export const getScrollbarWidth = () => {
+  if (cachedScrollbarWidth !== null) {
+    return cachedScrollbarWidth;
+  }
+
+  const scrollbarWidth = isMobile(window.innerWidth)
+    ? 0
+    : getActualScrollbarWidth();
+  cachedScrollbarWidth = scrollbarWidth;
+
+  return scrollbarWidth;
+};