diff --git a/theme/pagetoc.js b/theme/pagetoc.js
index 96d2b40..43dce07 100644
--- a/theme/pagetoc.js
+++ b/theme/pagetoc.js
@@ -51,7 +51,7 @@ window.addEventListener("scroll", updateFunction);
 if(document.querySelector("#document-not-found404")) {
   let timeLeft = 10;
 
-  setInterval(var timerId = function() {
+  var timerId = setInterval(() => {
     if(timeLeft == -1) {
       clearTimeout(timerId);
     } else {