1 files changed, 2 insertions, 3 deletions
diff --git a/static/clock.ts b/static/clock.ts
index a2d22e00..b0ddae00 100644
--- a/static/clock.ts
+++ b/static/clock.ts
@@ -2,9 +2,8 @@ export { SmallcalCellHighlight, Timebar }
 
 import { makeElement, date_to_percent } from './lib'
 
-class Clock {
-    update(now: Date) {
-    }
+abstract class Clock {
+    abstract update(now: Date): void;
 }