Only waitUntil scheduled module handler return if defined

Author: mrbbot

packages/core/src/standards/event.ts

@@ -335,7 +335,7 @@ export class ServiceWorkerGlobalScope extends WorkerGlobalScope {
       const controller = new ScheduledController(e.scheduledTime, e.cron);
       const ctx = new ExecutionContext(e);
       const res = listener(controller, this.#bindings, ctx);
-      e.waitUntil(Promise.resolve(res));
+      if (res !== undefined) e.waitUntil(Promise.resolve(res));
     });
   }
 

packages/core/test/standards/event.spec.ts

@@ -168,12 +168,25 @@ test("MiniflareCore: adds module scheduled event listener", async (t) => {
       return "returned";
     }
   }`;
-  const mf = useMiniflare(
+  let mf = useMiniflare(
     { BindingsPlugin },
     { modules: true, script, bindings: { KEY: "value" } }
   );
-  const res = await mf.dispatchScheduled(1000, "30 * * * *");
+  let res = await mf.dispatchScheduled(1000, "30 * * * *");
   t.deepEqual(res, [1000, "30 * * * *", "value", "that", "returned"]);
+
+  // Check returned value is only waitUntil'ed if it's defined
+  mf = useMiniflare(
+    { BindingsPlugin },
+    {
+      modules: true,
+      script: `export default { scheduled(controller, env, ctx) { 
+        ctx.waitUntil(42);
+      }}`,
+    }
+  );
+  res = await mf.dispatchScheduled(1000, "30 * * * *");
+  t.deepEqual(res, [42]);
 });
 
 test("kDispatchFetch: dispatches event", async (t) => {