diff --git a/apps/antonclk/app.js b/apps/antonclk/app.js
index 6197d66aa..4b1e71bda 100644
--- a/apps/antonclk/app.js
+++ b/apps/antonclk/app.js
@@ -99,7 +99,7 @@ function updateState() {
 }
 
 function isoStr(date) {
-  return date.getFullYear() + "-" + ("0" + (date.getMonth() + 1)).slice(-2) + "-" + ("0" + date.getDate()).substr(-2);
+  return date.getFullYear() + "-" + ("0" + (date.getMonth() + 1)).slice(-2) + "-" + ("0" + date.getDate()).slice(-2);
 }
 
 var calWeekBuffer = [false,false,false]; //buffer tz, date, week no (once calculated until other tz or date is requested)