Function onShellReady

packages/react-dom/src/__tests__/ReactDOMFizzServer-test.js:1542–1546

()

        {
          identifierPrefix: 'A_',
          onShellReady() {
            writableA.write('<div id="container-A">');
            pipe(writableA);
            writableA.write('</div>');
          },
        },
      );
    });