1 files changed, 1 insertions, 1 deletions
diff --git a/js/event_target.ts b/js/event_target.ts
index 87268383e..ba086d544 100644
--- a/js/event_target.ts
+++ b/js/event_target.ts
@@ -32,7 +32,7 @@ export class EventTarget implements domTypes.EventTarget {
     requiredArguments("EventTarget.removeEventListener", arguments.length, 2);
     if (hasOwnProperty(this.listeners, type) && callback !== null) {
       this.listeners[type] = this.listeners[type].filter(
-        listener => listener !== callback
+        (listener): boolean => listener !== callback
       );
     }
   }