diff --git a/frontend/src/js/test/focus.ts b/frontend/src/js/test/focus.ts
index eb2721155..b423086ab 100644
--- a/frontend/src/js/test/focus.ts
+++ b/frontend/src/js/test/focus.ts
@@ -5,7 +5,7 @@ import * as ActivePage from "../states/active-page";
 
 let state = false;
 
-export function set(foc: boolean, withCursor = false) {
+export function set(foc: boolean, withCursor = false): void {
   if (foc && !state) {
     state = true;
     Caret.stopAnimation();