diff --git a/frontend/files/index.html b/frontend/files/index.html
index 05718ac..a0ac314 100644
--- a/frontend/files/index.html
+++ b/frontend/files/index.html
@@ -158,14 +158,7 @@
ISBN = EAN.slice(3, 12);
var checkdigit =
(11 -
- (_.reduce(
- ISBN.split(""),
- function (sum, num, key) {
- return sum + num * (10 - key);
- },
- 0
- ) %
- 11)) %
+ (_.reduce(ISBN.split(""), (s, n, k) => s + n * (10 - k), 0) % 11)) %
11;
return ISBN + (checkdigit == 10 ? "X" : checkdigit);
}