fix(lineNumbers): make $el property optional in LineNumbersState interface

src/alpine/lineNumbers.ts

@@ -95,7 +95,7 @@ function appendElementLines(
 }
 
 interface LineNumbersState {
-  $el: HTMLElement;
+  $el?: HTMLElement;
   totalLines: number;
   resizeObserver: ResizeObserver | null;
   init(): void;
@@ -144,12 +144,13 @@ export const lineNumbers = (): LineNumbersState => ({
   },
 
   calculateLineNumbers() {
-    const content = (this.$el as HTMLElement).querySelector('.post-content') as HTMLElement;
-    const gutter = (this.$el as HTMLElement).querySelector('.post-line-gutter') as HTMLElement;
+    const content = this.$el?.querySelector('.post-content') as HTMLElement;
+    const gutter = this.$el?.querySelector('.post-line-gutter') as HTMLElement;
+
     if (!content || !gutter) return;
 
     const defaultLineHeight = getDefaultLineHeight(content);
-    const container = content.querySelector(':scope > div') as HTMLElement || content;
+    const container = content.querySelector(':scope > div') || content;
     const blockElements = container.querySelectorAll(':scope > *');
 
     gutter.innerHTML = '';