fix: 當主頁設置不顯示頂部圖時,js報錯的bug

package.json

@@ -1,6 +1,6 @@
 {
   "name": "hexo-theme-butterfly",
-  "version": "3.4.0-b3",
+  "version": "3.4.0-b4",
   "description": "A Simple and Card UI Design theme for Hexo",
   "main": "package.json",
   "scripts": {

source/js/main.js

@@ -71,7 +71,8 @@ document.addEventListener('DOMContentLoaded', function () {
  * 首頁top_img底下的箭頭
  */
   const scrollDownInIndex = () => {
-    document.getElementById('scroll-down').addEventListener('click', function () {
+    const $scrollDownEle = document.getElementById('scroll-down')
+    $scrollDownEle && $scrollDownEle.addEventListener('click', function () {
       btf.scrollToDest(document.getElementById('content-inner').offsetTop, 300)
     })
   }