*Execution — Browser Debugging with Playwright · MediaWiki*

Use Playwright inside the running wiki container to debug client-side behaviour
that is not visible in PHP logs or HTML source: ResourceLoader module states,
DOM state after JS execution, JS runtime errors, and user interaction (clicks,
form submission).

Use this approach when:

* Verifying that a ResourceLoader module is registered and loaded (`ready`) after a server-side change
* Checking whether a JS-rendered widget (tabs, dropdowns, dialogs) actually appears in the DOM
* Catching uncaught JS exceptions (`pageerror`) or console warnings during page load
* Simulating user interaction (clicking a tab, submitting a form) and inspecting the resulting JS state

For HTTP response analysis or HTML source inspection, `curl` from inside the
container is sufficient and faster.

*Get the container name:*

[source,console]
----
docker ps --format '{{.Names}}'
----

*One-time setup* (idempotent, safe to repeat):

[source,console]
----
docker exec <container> bash -c "apt-get update && apt-get install -y nodejs npm chromium"
docker exec <container> bash -c "cd /tmp && npm install playwright"
----

*Script template* — create `/tmp/pw.js` inside the container:

[source,console]
----
docker exec <container> bash -c "cat > /tmp/pw.js" <<'EOF'
const { chromium } = require('/tmp/node_modules/playwright');
(async () => {
    const browser = await chromium.launch({
        executablePath: '/usr/bin/chromium',
        args: ['--no-sandbox', '--disable-setuid-sandbox']
    });
    const page = await browser.newPage();
    page.on('pageerror', err => console.log('PAGEERROR:', err.message));
    page.on('console', msg => console.log('CONSOLE:', msg.type(), msg.text()));

    await page.goto('http://127.0.0.1/index.php/...', { waitUntil: 'networkidle', timeout: 30000 });

    // Read JS state
    const state = await page.evaluate(() =>
        mw.loader.moduleRegistry['ext.mymodule']?.state
    );
    console.log('module state:', state);

    // Simulate interaction
    await page.click('.some-selector');

    await browser.close();
})().catch(e => { console.error(e.message); process.exit(1); });
EOF
----

*Run the script:*

[source,console]
----
docker exec <container> node /tmp/pw.js
----

NOTE: Use `http://127.0.0.1` (not the public hostname) — no authentication is
required when accessing the wiki from within the container.

NOTE: `/tmp/pw.js` does not survive a container restart. Re-create it from the
template above if needed.