Fix react example

Author: wycats

src/frameworks/react/$snippets/resources.tsx

@@ -1,20 +1,20 @@
 import "@typescript/lib-dom";
 
 // #region stopwatch
-import { Cell, Resource } from "@starbeam/universal";
+import { Cell, Formula, Resource } from "@starbeam/universal";
 
-const Stopwatch = Resource((r) => {
+const Stopwatch = Resource(({ on }) => {
   const time = Cell(new Date());
 
-  r.on.setup(() => {
-    const interval = setInterval(() => {
-      time.set(new Date());
-    });
+  const interval = setInterval(() => {
+    time.set(new Date());
+  });
 
+  on.cleanup(() => {
     return () => clearInterval(interval);
   });
 
-  return () => {
+  return Formula(() => {
     const now = time.current;
 
     return new Intl.DateTimeFormat("en-US", {
@@ -23,17 +23,17 @@ const Stopwatch = Resource((r) => {
       second: "numeric",
       hour12: false,
     }).format(now);
-  };
+  });
 });
 // #endregion stopwatch
 
 // #region component
-import { useResource } from "@starbeam/react";
+import { use } from "@starbeam/react";
 
 export const Clock = () => {
   // #highlight:next
-  const time = useResource(() => Stopwatch);
+  const time = use(() => Stopwatch, []);
 
-  return <div>{time}</div>;
+  return <div>{time ?? "now"}</div>;
 };
 // #endregion app