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* Hydration analysis: inspects the server-rendered HTML of a running app.
*
* It fetches the page and counts the markers Coherent.js hydration relies
* on. It cannot see hydration mismatches — those only exist once the page
* runs in a browser, where hydrate() reports them in the console — so it
* never claims to have found or ruled any out.
*/
/** Attributes that mark server-rendered output as hydratable. */
const HYDRATION_MARKERS = [
'data-coherent-component',
'data-coherent-island',
'data-hydratable',
'data-hydrate',
'data-hydration-id',
'data-state',
];
function countAttribute(html, name) {
const pattern = new RegExp(`\\s${name}(?=[\\s=/>])`, 'gi');
return (html.match(pattern) || []).length;
}
function escapeRegExp(text) {
return text.replace(/[.*+?^${}()|[\]\\]/g, '\\$&');
}
/**
* @param {Object} [options]
* @param {string} [options.url='http://localhost:3000'] - Page to inspect.
* @param {string} [options.components] - Comma-separated component names to look for.
* @param {boolean} [options.compare] - Not supported yet (reported as an error).
* @param {number} [options.timeoutMs=10000] - Request timeout.
*/
export async function analyzeHydration(options = {}) {
const url = options.url || 'http://localhost:3000';
const analysis = {
timestamp: new Date().toISOString(),
type: 'hydration-analysis',
summary: { url },
details: {},
recommendations: [],
};
if (options.compare) {
analysis.summary.status = 'error';
analysis.summary.error =
'--compare (server vs. client output) is not implemented yet. ' +
'Run the page in a browser: hydrate() logs mismatches to the console in development.';
return analysis;
}
let response;
let html;
const started = performance.now();
try {
response = await globalThis.fetch(url, {
signal: globalThis.AbortSignal.timeout(options.timeoutMs ?? 10_000),
});
html = await response.text();
} catch (error) {
analysis.summary.status = 'error';
analysis.summary.error = `Could not fetch ${url}: ${error.cause?.code || error.cause?.message || error.message}. Start the app first, or pass --url.`;
return analysis;
}
analysis.summary.httpStatus = response.status;
analysis.summary.responseTime = `${Math.round(performance.now() - started)}ms`;
analysis.summary.bytes = Buffer.byteLength(html);
if (!response.ok) {
analysis.summary.status = 'error';
analysis.summary.error = `${url} answered HTTP ${response.status}`;
return analysis;
}
const contentType = response.headers.get('content-type') || '';
Iif (!contentType.includes('html')) {
analysis.summary.status = 'error';
analysis.summary.error = `${url} did not return HTML (content-type: ${contentType || 'none'})`;
return analysis;
}
const markers = Object.fromEntries(
HYDRATION_MARKERS.map((name) => [name, countAttribute(html, name)])
);
const total = Object.values(markers).reduce((sum, n) => sum + n, 0);
analysis.summary.hydrationMarkers = total;
analysis.details.markers = markers;
if (options.components) {
const names = String(options.components)
.split(',')
.map((n) => n.trim())
.filter(Boolean);
analysis.details.components = Object.fromEntries(
names.map((name) => {
const pattern = new RegExp(
`data-(?:coherent-component|coherent-island-component|hydrate)=["']${escapeRegExp(name)}["']`,
'g'
);
return [name, (html.match(pattern) || []).length];
})
);
for (const [name, count] of Object.entries(analysis.details.components)) {
if (count === 0) {
analysis.recommendations.push({
type: 'hydration',
priority: 'medium',
message: `No element on ${url} is marked as component "${name}".`,
});
}
}
}
analysis.summary.status = total > 0 ? 'success' : 'warning';
if (total === 0) {
analysis.recommendations.push({
type: 'hydration',
priority: 'medium',
message:
'No hydration markers found: the page is static HTML, so there is nothing for the client to hydrate.',
});
}
analysis.recommendations.push({
type: 'info',
priority: 'low',
message:
'This inspects server HTML only. Mismatches show up in the browser console, where hydrate() reports them in development.',
});
return analysis;
}
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