Fix error with incorrect setTimeout/setInterval callback type

Author: mrbbot

packages/core/src/standards/timers.ts

@@ -14,10 +14,12 @@ export function createTimer<Return>(
   return (callback, ms, ...args) => {
     if (blockGlobalTimers) assertInRequest();
     return func(
-      async (...args) => {
-        await waitForOpenInputGate();
-        callback(...args);
-      },
+      callback
+        ? async (...args) => {
+            await waitForOpenInputGate();
+            callback?.(...args);
+          }
+        : callback,
       ms,
       ...args
     );

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

@@ -29,6 +29,12 @@ test("inputGatedSetTimeout: waits for input gate to open before calling callback
   });
   t.deepEqual(result, [42, "test"]);
 });
+test("inputGatedSetTimeout: throws without a callback", (t) => {
+  // @ts-expect-error intentionally testing incorrect types
+  t.throws(() => inputGatedSetTimeout(), {
+    code: "ERR_INVALID_CALLBACK",
+  });
+});
 
 test("inputGatedSetInterval: calls callback with no input gate in context", async (t) => {
   let [trigger, promise] = triggerPromise<[number, string]>();