Keep a mutable value without rendering on each write.
Keep a mutable value without rendering on each write with a small React component and explicit browser behavior.
import { useState, useRef } from 'react';
export default function App() {
const clicks = useRef(0);
const [shown, setShown] = useState(0);
return (
<main data-ready>
<button onClick={() => { clicks.current++; setShown(clicks.current); }}>Count</button><output>{shown}</output>
</main>
);
}Expected output EXAMPLE
Click the button. The output displays “1”.
Details
Use this App.jsx in a React 19 project with JSX support. Mount the default App component with createRoot in your existing entry point. The test mounts this exact component and checks its rendered behavior.
Tested on Ubuntu 24.04.3 LTS · · Node.js v24.15.0; Chromium 141.0.7390.37 · esbuild 0.28.2; playwright 1.56.0; react 19.3.1; react-dom 19.3.1
Test inputs, results and environment
The exact published code ran in a dedicated Linux test container with prepared inputs. Dedicated test container, external networking disabled, read-only root, temporary per-example working directory. Browser network requests are blocked. Fixtures and output records are isolated from the application database. Testing covers this example and its stated checks, not every input, operating system, or runtime version. The Linux container shares its host's kernel; this is not a native Windows test.
- Architecture / host kernel
- x86_64 / 6.18.54.1-microsoft-standard-WSL2
- Snippet identity / locale
- uid=65534, gid=65534 (unprivileged) / C.UTF-8
- Interpreter invocation
bundle the exact published component with esbuild; mount it in Chromium and execute browser assertions- Container image ID
sha256:c9bce90110f636fe04907469a37e9c8ac888171fd569cbf87101743ec7cdf099- Code SHA-256
885da3337a3bd08dab79585adebd6dfc38a0397919e9e1e6c762006138a48139- Dependencies
- esbuild 0.28.2; playwright 1.56.0; react 19.3.1; react-dom 19.3.1
Test input setup
These are the prepared inputs used by the test harness. See Details above for the prerequisites and how to run this example.
The harness supplies index.html and mounts the published component with locally installed, pinned dependencies.
Observed standard output
Expected output describes the rendered page. The standard-output record below is the browser test harness receipt; the additional assertions check the result and interactions.
Keep a mutable value without rendering on each write: browser checks passed.
Exit code: 0. Standard error: empty. Validation: Shape/content assertions. System-dependent values above are one recorded run.
Additional assertions that passed
Checks recorded by the test harness. Where Python assertions are shown, browser cases use Playwright and simulator cases may inspect pin transitions: result.stdout is captured output, work is the temporary directory, and Path is pathlib.Path. The harness also imports json and csv.
await page.getByRole('button').click(); await text('output', '1');