Subscribe to and clean up a window event.
Subscribe to and clean up a window event with a small React component and explicit browser behavior.
import { useState, useEffect } from 'react';
export default function App() {
const [count, setCount] = useState(0);
useEffect(() => {
const onPing = () => setCount(value => value + 1);
window.addEventListener("snippet-ping", onPing);
return () => window.removeEventListener("snippet-ping", onPing);
}, []);
return (
<main data-ready>
<output>{count}</output>
</main>
);
}Expected output EXAMPLE
Dispatch a snippet-ping event on window. The subscribed component updates its output from 0 to 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
622354690ab0a251ee6223d8cedd0c70f5e5bcf415a2d785d9a5f67a2fad923d- 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.
Subscribe to and clean up a window event: 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.evaluate(() => window.dispatchEvent(new Event('snippet-ping'))); await text('output', '1');