Ejemplo
react-dom 19.0.0: Preload resources and preconnect DNS using React 19 ReactDOM resource preloading APIs
Muestra verificada para npm react-dom 19.0.0: Preload resources and preconnect DNS using React 19 ReactDOM resource preloading APIs. El contrato se ejecutó…
sha256:d34bff97d3416d5ffdea11da4a16174eb77ed920db861295665067b0f1f4202e
Esta red ofrece una sola cosa: una muestra que compila. La ejecutó en un sandbox y guardó el recibo firmado. No califica ni garantiza nada: si el mismo código compila donde estás no es algo que haya medido.
Cuántas claves de firma distintas presentaron un recibo de contrato aprobado. Una es solo el autor; más de una significa que alguien más también lo compiló. Una clave se genera sola y no tiene identidad registrada detrás, así que cuenta claves, no personas.
MIT-0
Evidencia de ejecución
El entorno declarado y las ejecuciones firmadas se muestran por separado, para que veas exactamente qué ejecutó esta muestra y dónde.
- Base de evidencia
- Contrato firmado aprobado
- Recibos de verificación
- 1
- Claves de firma que lo compilaron
- 1
Entorno declarado
node 22.23 linux 24 · ubuntu · glibc 2.39 x64 node 22.23 javascript npm 10
Entornos de las ejecuciones de verificación
| Entorno | Contrato | Etapas | Ejecución |
|---|---|---|---|
| node 22 · linux alpine/x64 · docker ed25519:c1973797be207ac4 | PASS | compile:SKIPPED · contract:PASS · load:PASS · resolve:PASS CONTAINER_RUN · node-typescript@1node:22-alpine@sha256:c610fcdfb1d5… |
2026-08-27 |
Caso
HOW- Objetivo
- Preload resources and preconnect DNS using React 19 ReactDOM resource preloading APIs
- Paquetes
- Símbolos
-
- preconnect
- prefetchDNS
- preinit
- preload
- Entorno
- node 22.23.2
- Creado
- 2026-08-27T16:53:15Z
Contrato
- prefetchDNS, preconnect, preload, and preinit are exported from react-dom
- resource preloading calls during SSR emit hoisted link and async script tags in output HTML
- resource preloading calls during client render dynamically inject link and script tags into document.head
- duplicate resource preloading calls across multiple components in the render tree are deduplicated in document.head
- preinit style injects link stylesheet with data-precedence attribute while preload font injects link preload with as and type
Archivos
- NOTES.md
- PROMPT.md
- csx.json
- package-lock.json
- package.json
- spec.json
- src/index.mjs
- test/contract.mjs
Código fuente
# React 19 ReactDOM Resource Preloading APIs
## Prior CSX search
`search_known_solution` returned `NO_SAFE_MATCH` for React 19 resource preloading APIs (`prefetchDNS`, `preconnect`, `preload`, `preinit`). Existing samples only covered client roots/portals, SSR attribute dropping, and `defaultProps` removal.
## The tempting wrong model
1. Assuming `prefetchDNS`, `preconnect`, `preload`, and `preinit` require manual DOM node construction or third-party head management libraries.
2. Assuming multiple component calls for identical resource URLs produce duplicate `<link>` or `<script>` tags in `<head>` or SSR output.
3. Confusing `preload` (which emits `<link rel="preload">` hints) with `preinit` (which actively loads `<link rel="stylesheet">` or `<script async>`).
## Observable failure and verified behavior
- During SSR (`renderToString` / `renderToStaticMarkup`), preloading calls within components are hoisted to the top of the rendered HTML output.
- During client rendering (`createRoot`), preloading calls within components dynamically insert the corresponding `<link>` and `<script>` elements into `document.head`.
- Redundant calls across different components for identical resource URLs are automatically deduplicated by the React 19 DOM runtime.
- `preinit(href, { as: 'style', precedence })` injects `<link rel="stylesheet" data-precedence="...">` whereas `preload(href, { as: 'font', type })` injects `<link rel="preload" as="font" type="...">`.
Clean-room public code sample — generation instructions
Write a brand-new, minimal, self-contained code sample in this clean-room directory.
Do not copy, paraphrase, or reference any existing project source. Work only from this spec.
A csx.json manifest scaffold already exists. Do not recreate it from memory. Preserve its case.goal, packages and symbols; fill its empty case.contract with exact assertions and correct its environment, commands and verifierAdapter for the files you generate.
Goal: Preload resources and preconnect DNS using React 19 ReactDOM resource preloading APIs
Kind: HOW
Use EXACTLY these public packages and versions:
- pkg:npm/react-dom@19.0.0
Demonstrate these symbols/APIs:
- preconnect
- prefetchDNS
- preinit
- preload
Constraints:
- executionContext: node
Required runtime conditions:
- ecosystem: npm
- language: javascript
- moduleSystem: cjs
- packageManager: npm@10.9.8
- runtime: node@22.23.2
Rules:
- One focused purpose; the smallest project that proves the goal.
- Include a contract test (test/contract.*) that runs OFFLINE and exits 0 exactly when the goal behavior works.
- Pin every dependency with a lockfile so resolution is reproducible.
- No secrets, credentials, or tokens. No real URLs (only example.com or localhost). No absolute paths.
- No personal names, emails, company names, or project identifiers of any kind.
- No binaries and no generated output (node_modules, dist, target, venv, .git, .env).
- Keep it under 200 files and 256KB packed.
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{
"name": "sample-react-dom-resource-preloading",
"version": "1.0.0",
"private": true,
"type": "module",
"license": "MIT-0",
"scripts": {
"test": "node test/contract.mjs"
},
"dependencies": {
"react": "19.0.0",
"react-dom": "19.0.0"
},
"devDependencies": {
"jsdom": "^26.0.0"
}
}
{
"schemaVersion": 1,
"goal": "Preload resources and preconnect DNS using React 19 ReactDOM resource preloading APIs",
"kind": "HOW",
"packages": [
"pkg:npm/react-dom@19.0.0"
],
"symbols": [
"preconnect",
"prefetchDNS",
"preinit",
"preload"
],
"constraints": {
"executionContext": "node"
},
"runtimeConditions": {
"ecosystem": "npm",
"language": "javascript",
"moduleSystem": "cjs",
"packageManager": "npm@10.9.8",
"runtime": "node@22.23.2"
}
}
import React from 'react';
import {
prefetchDNS,
preconnect,
preload,
preinit,
preloadModule,
preinitModule,
} from 'react-dom';
/**
* Component that registers external DNS and connection preloading during render
*/
export function ConnectionPreloader({ domain, apiOrigin }) {
if (domain) {
prefetchDNS(domain);
}
if (apiOrigin) {
preconnect(apiOrigin, { crossOrigin: 'anonymous' });
}
return React.createElement('span', { 'data-testid': 'connection-preloader' });
}
/**
* Component that registers asset preloads, stylesheets, and scripts during render
*/
export function AssetPreloader({ fontUrl, stylesheetUrl, scriptUrl, moduleUrl }) {
if (fontUrl) {
preload(fontUrl, { as: 'font', type: 'font/woff2', crossOrigin: 'anonymous' });
}
if (stylesheetUrl) {
preinit(stylesheetUrl, { as: 'style', precedence: 'default' });
}
if (scriptUrl) {
preinit(scriptUrl, { as: 'script' });
}
if (moduleUrl) {
preloadModule(moduleUrl, { as: 'script' });
}
return React.createElement('span', { 'data-testid': 'asset-preloader' });
}
export { prefetchDNS, preconnect, preload, preinit, preloadModule, preinitModule };
import assert from 'node:assert/strict';
import { JSDOM } from 'jsdom';
// Setup DOM environment
const dom = new JSDOM(
'<!doctype html><html><head><title>Resource Preload Test</title></head><body><div id="root"></div></body></html>',
{ url: 'https://example.com/' }
);
globalThis.window = dom.window;
globalThis.document = dom.window.document;
const React = await import('react');
const ReactDOM = await import('react-dom');
const ReactDOMServer = await import('react-dom/server');
const ReactDOMClient = await import('react-dom/client');
const {
ConnectionPreloader,
AssetPreloader,
prefetchDNS,
preconnect,
preload,
preinit,
preloadModule,
} = await import('../src/index.mjs');
// Contract 1: prefetchDNS, preconnect, preload, and preinit are exported from react-dom
assert.equal(typeof prefetchDNS, 'function', 'prefetchDNS must be exported from react-dom');
assert.equal(typeof preconnect, 'function', 'preconnect must be exported from react-dom');
assert.equal(typeof preload, 'function', 'preload must be exported from react-dom');
assert.equal(typeof preinit, 'function', 'preinit must be exported from react-dom');
assert.equal(typeof preloadModule, 'function', 'preloadModule must be exported from react-dom');
// Contract 2: resource preloading calls during SSR emit hoisted link and async script tags in output HTML
function SSRApp() {
return React.createElement(
'div',
null,
React.createElement(ConnectionPreloader, {
domain: 'https://ssr-dns.example.com',
apiOrigin: 'https://ssr-conn.example.com',
}),
React.createElement(AssetPreloader, {
fontUrl: 'https://ssr-cdn.example.com/font.woff2',
stylesheetUrl: 'https://ssr-cdn.example.com/theme.css',
scriptUrl: 'https://ssr-cdn.example.com/bundle.js',
moduleUrl: 'https://ssr-cdn.example.com/worker.js',
})
);
}
const ssrOutput = ReactDOMServer.renderToStaticMarkup(React.createElement(SSRApp));
assert.ok(
ssrOutput.includes('<link href="https://ssr-dns.example.com" rel="dns-prefetch"/>'),
'SSR must emit dns-prefetch link tag'
);
assert.ok(
ssrOutput.includes('<link rel="preconnect" href="https://ssr-conn.example.com" crossorigin=""/>'),
'SSR must emit preconnect link tag'
);
assert.ok(
ssrOutput.includes('<link rel="preload" href="https://ssr-cdn.example.com/font.woff2" as="font" crossorigin="" type="font/woff2"/>'),
'SSR must emit preload font link tag'
);
assert.ok(
ssrOutput.includes('<link rel="stylesheet" href="https://ssr-cdn.example.com/theme.css" data-precedence="default"/>'),
'SSR must emit stylesheet link tag with data-precedence for preinit style'
);
assert.ok(
ssrOutput.includes('<script src="https://ssr-cdn.example.com/bundle.js" async=""></script>'),
'SSR must emit async script tag for preinit script'
);
assert.ok(
ssrOutput.includes('<link rel="modulepreload" href="https://ssr-cdn.example.com/worker.js"/>'),
'SSR must emit modulepreload link tag for preloadModule'
);
// Contract 3: resource preloading calls during client render dynamically inject link and script tags into document.head
function ClientApp() {
return React.createElement(
'main',
null,
React.createElement(ConnectionPreloader, {
domain: 'https://client-api.example.com',
apiOrigin: 'https://client-cdn.example.com',
}),
React.createElement(AssetPreloader, {
fontUrl: 'https://client-cdn.example.com/inter.woff2',
stylesheetUrl: 'https://client-cdn.example.com/app.css',
scriptUrl: 'https://client-cdn.example.com/analytics.js',
}),
// Duplicate preloader components to test deduplication across the render tree
React.createElement(ConnectionPreloader, {
domain: 'https://client-api.example.com',
apiOrigin: 'https://client-cdn.example.com',
}),
React.createElement(AssetPreloader, {
fontUrl: 'https://client-cdn.example.com/inter.woff2',
stylesheetUrl: 'https://client-cdn.example.com/app.css',
scriptUrl: 'https://client-cdn.example.com/analytics.js',
})
);
}
const rootContainer = document.getElementById('root');
const root = ReactDOMClient.createRoot(rootContainer);
ReactDOM.flushSync(() => {
root.render(React.createElement(ClientApp));
});
// Contract 4: duplicate resource preloading calls across multiple components in the render tree are deduplicated in document.head
const dnsLinks = document.querySelectorAll('link[rel="dns-prefetch"][href="https://client-api.example.com"]');
assert.equal(dnsLinks.length, 1, 'Client render must insert 1 deduplicated dns-prefetch link');
const preconnectLinks = document.querySelectorAll('link[rel="preconnect"][href="https://client-cdn.example.com"]');
assert.equal(preconnectLinks.length, 1, 'Client render must insert 1 deduplicated preconnect link');
assert.equal(preconnectLinks[0].getAttribute('crossorigin'), '');
const preloadLinks = document.querySelectorAll('link[rel="preload"][href="https://client-cdn.example.com/inter.woff2"]');
assert.equal(preloadLinks.length, 1, 'Client render must insert 1 deduplicated preload link');
// Contract 5: preinit style injects link stylesheet with data-precedence attribute while preload font injects link preload with as and type
assert.equal(preloadLinks[0].getAttribute('as'), 'font');
assert.equal(preloadLinks[0].getAttribute('type'), 'font/woff2');
const stylesheetLinks = document.querySelectorAll('link[rel="stylesheet"][href="https://client-cdn.example.com/app.css"]');
assert.equal(stylesheetLinks.length, 1, 'preinit style must inject stylesheet link into head');
assert.equal(stylesheetLinks[0].getAttribute('data-precedence'), 'default');
const scriptTags = document.querySelectorAll('script[src="https://client-cdn.example.com/analytics.js"]');
assert.equal(scriptTags.length, 1, 'preinit script must inject async script into head');
assert.equal(scriptTags[0].getAttribute('async'), '');
root.unmount();
console.log('CONTRACT PASS: React 19 resource preloading and preconnect DNS verified');
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