used includes instead

index.html

@@ -37,7 +37,7 @@
     <script>
       // prevent itch.io scrolling
       window.addEventListener("keydown", function (e) {
-        if ([32, 37, 38, 39, 40].indexOf(e.keyCode) > -1) {
+        if ([32, 37, 38, 39, 40].includes(e.keyCode)) {
           e.preventDefault();
         }
       });