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react-dom 19.0.0: Preload resources and preconnect DNS using React 19 ReactDOM resource preloading APIs

검증된 샘플 — npm react-dom 19.0.0: Preload resources and preconnect DNS using React 19 ReactDOM resource preloading APIs. node 22 · linux alpine/x64 · docker에서…

sha256:d34bff97d3416d5ffdea11da4a16174eb77ed920db861295665067b0f1f4202e

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서명된 컨트랙트 통과
검증 영수증
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빌드한 서명 키
1
선언된 환경 node 22.23 linux 24 · ubuntu · glibc 2.39 x64 node 22.23 javascript npm 10

검증 실행 환경

환경 컨트랙트 단계 실행일
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

케이스

HOW
목표
Preload resources and preconnect DNS using React 19 ReactDOM resource preloading APIs
패키지
심벌
  • preconnect
  • prefetchDNS
  • preinit
  • preload
환경
node 22.23.2
생성일
2026-08-27T16:53:15Z

컨트랙트

  1. prefetchDNS, preconnect, preload, and preinit are exported from react-dom
  2. resource preloading calls during SSR emit hoisted link and async script tags in output HTML
  3. resource preloading calls during client render dynamically inject link and script tags into document.head
  4. duplicate resource preloading calls across multiple components in the render tree are deduplicated in document.head
  5. preinit style injects link stylesheet with data-precedence attribute while preload font injects link preload with as and type

파일

  • NOTES.md
  • PROMPT.md
  • csx.json
  • package-lock.json
  • package.json
  • spec.json
  • src/index.mjs
  • test/contract.mjs

소스 아티팩트 내려받기 (tar.gz)

소스

NOTES.md
# 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="...">`.
PROMPT.md
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.
csx.json
{"case":{"caseId":"case:sha256:dc0c1eac618fb318ece0d341784835f358323ebf374e500e37b3d84d88a77116","constraints":{"executionContext":"node"},"contract":["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"],"goal":"Preload resources and preconnect DNS using React 19 ReactDOM resource preloading APIs","kind":"HOW","packages":["pkg:npm/react-dom@19.0.0"],"schemaVersion":1,"symbols":["preconnect","prefetchDNS","preinit","preload"]},"contractCommand":["node","test/contract.mjs"],"environment":{"arch":"x64","distro":"ubuntu","ecosystem":"npm","executionContext":"node","language":"javascript","libc":"glibc","libcVersion":"2.39","moduleSystem":"esm","os":"linux","osVersionBucket":"24","packageManager":"npm","packageManagerVersion":"10.9.8","runtime":"node","runtimeVersion":"22.23.2","schemaVersion":1},"license":"MIT-0","packages":["pkg:npm/react-dom@19.0.0"],"schemaVersion":1,"subject":"pkg:npm/react-dom@19.0.0","symbols":["preconnect","prefetchDNS","preinit","preload"],"verifierAdapter":"node-typescript@1"}
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package.json
{
  "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"
  }
}
spec.json
{
  "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"
  }
}
src/index.mjs
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 };
test/contract.mjs
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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