[Flight] Serialize top-level Date

packages/react-client/src/__tests__/ReactFlight-test.js

@@ -661,6 +661,18 @@ describe('ReactFlight', () => {
       `);
   });
 
+  it('can transport Date as a top-level value', async () => {
+    const date = new Date(0);
+    const transport = ReactNoopFlightServer.render(date);
+
+    let readValue;
+    await act(async () => {
+      readValue = await ReactNoopFlightClient.read(transport);
+    });
+
+    expect(readValue).toEqual(date);
+  });
+
   it('can transport Error objects as values', async () => {
     function ComponentClient({prop}) {
       return `

packages/react-server/src/ReactFlightServer.js

@@ -1962,6 +1962,12 @@ function serializeUndefined(): string {
   return '$undefined';
 }
 
+function serializeDate(date: Date): string {
+  // JSON.stringify automatically calls Date.prototype.toJSON which calls toISOString.
+  // We need only tack on a $D prefix.
+  return '$D' + date.toJSON();
+}
+
 function serializeDateFromDateJSON(dateJSON: string): string {
   // JSON.stringify automatically calls Date.prototype.toJSON which calls toISOString.
   // We need only tack on a $D prefix.
@@ -2779,6 +2785,14 @@ function renderModelDestructive(
       }
     }
 
+    // We put the Date check low b/c most of the time Date's will already have been serialized
+    // before we process it in this function but when rendering a Date() as a top level it can
+    // end up being a Date instance here. This is rare so we deprioritize it by putting it deep
+    // in this function
+    if (value instanceof Date) {
+      return serializeDate(value);
+    }
+
     // Verify that this is a simple plain object.
     const proto = getPrototypeOf(value);
     if (
@@ -3646,6 +3660,10 @@ function renderConsoleValue(
     return serializeBigInt(value);
   }
 
+  if (value instanceof Date) {
+    return serializeDate(value);
+  }
+
   return 'unknown type ' + typeof value;
 }