CodeSampleX

Ejemplo

react-dom 19.0.0: flushSync

Muestra verificada para npm react-dom 19.0.0: flushSync. El contrato se ejecutó en node 22 · linux debian/x64 · docker y pasó.

sha256:ee9daa6e0f56b0b611eb07a2dff2d65ebe8bfb24350f1b5d19057bdc82b47230

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 linux 24 · ubuntu · glibc 2.39 x64 npm

Entornos de las ejecuciones de verificación

Entorno Contrato Etapas Ejecución
node 22 · linux debian/x64 · docker ed25519:c1973797be207ac4 PASS compile:SKIPPED · contract:PASS · load:PASS · resolve:PASS
CONTAINER_RUN · node-typescript@1node:22@sha256:8a34c4ab3ea2…		 2026-09-06

Caso

HOW
Objetivo
verify react-dom.flushSync in pkg:npm/react-dom@19.0.0
Paquetes
Símbolos
  • react-dom.flushSync
Creado
2026-09-06T22:10:44Z

Contrato

  1. flushSync is exported as a function from the react-dom entrypoint
  2. flushSync executes the provided callback synchronously and returns its return value
  3. flushSync around root.render commits the root DOM synchronously before flushSync returns
  4. flushSync around state updates commits component state changes synchronously to the DOM
  5. flushSync re-throws exceptions thrown by its callback
  6. flushSync called without arguments returns undefined

Archivos

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

Descargar el artefacto de código fuente (tar.gz)

Código fuente

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: verify react-dom.flushSync in pkg:npm/react-dom@19.0.0
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:npm/react-dom@19.0.0
Demonstrate these symbols/APIs:
  - react-dom.flushSync

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:a73a027a1c2b41fbb974c8546c38018612a501e6bb38b35d22b5df8ad7ef5b49","contract":["flushSync is exported as a function from the react-dom entrypoint","flushSync executes the provided callback synchronously and returns its return value","flushSync around root.render commits the root DOM synchronously before flushSync returns","flushSync around state updates commits component state changes synchronously to the DOM","flushSync re-throws exceptions thrown by its callback","flushSync called without arguments returns undefined"],"goal":"verify react-dom.flushSync in pkg:npm/react-dom@19.0.0","kind":"HOW","packages":["pkg:npm/react-dom@19.0.0"],"schemaVersion":1,"symbols":["react-dom.flushSync"]},"contractCommand":["node","test/contract.mjs"],"environment":{"arch":"x64","distro":"ubuntu","ecosystem":"npm","libc":"glibc","libcVersion":"2.39","os":"linux","osVersionBucket":"24","packageManager":"npm","schemaVersion":1},"license":"MIT-0","packages":["pkg:npm/react-dom@19.0.0"],"schemaVersion":1,"subject":"pkg:npm/react-dom@19.0.0","symbols":["react-dom.flushSync"],"verifierAdapter":"node-typescript@1"}
index.js
import { flushSync } from 'react-dom';

/**
 * Executes a callback synchronously within React's flushSync boundary,
 * forcing any pending updates to be committed to the DOM before returning.
 *
 * @template T
 * @param {() => T} [fn] - The function to execute synchronously.
 * @returns {T | undefined} The return value of the callback, or undefined if no callback is passed.
 */
export function runSync(fn) {
  return flushSync(fn);
}

export { flushSync };
package-lock.json
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package.json
{
  "name": "sample-react-dom-flushsync",
  "version": "1.0.0",
  "description": "Clean-room sample verifying react-dom flushSync",
  "main": "index.js",
  "type": "module",
  "license": "MIT-0",
  "dependencies": {
    "react": "19.0.0",
    "react-dom": "19.0.0"
  },
  "devDependencies": {
    "jsdom": "29.1.1"
  }
}
spec.json
{
  "schemaVersion": 1,
  "goal": "verify react-dom.flushSync in pkg:npm/react-dom@19.0.0",
  "kind": "HOW",
  "packages": [
    "pkg:npm/react-dom@19.0.0"
  ],
  "symbols": [
    "react-dom.flushSync"
  ]
}
test/contract.mjs
import assert from 'node:assert/strict';
import { JSDOM } from 'jsdom';
import React, { useState } from 'react';
import * as ReactDOM from 'react-dom';
import { flushSync } from 'react-dom';
import { createRoot } from 'react-dom/client';
import { runSync } from '../index.js';

// 1. flushSync is exported as a function from the react-dom entrypoint
assert.equal(typeof ReactDOM.flushSync, 'function', 'ReactDOM.flushSync should be a function');
assert.equal(typeof flushSync, 'function', 'flushSync should be a function');
assert.equal(typeof runSync, 'function', 'runSync helper should be a function');

// 2. flushSync executes the provided callback synchronously and returns its return value
const result = flushSync(() => 42);
assert.equal(result, 42, 'flushSync should return the value returned by its callback');

const helperResult = runSync(() => 'synced');
assert.equal(helperResult, 'synced', 'runSync should return callback return value');

// 3. flushSync around root.render commits the root DOM synchronously before flushSync returns
const dom = new JSDOM('<!doctype html><html><body><div id="app"></div></body></html>', {
  url: 'https://example.com/',
});
const priorGlobals = new Map();
for (const name of ['window', 'document']) {
  priorGlobals.set(name, Object.getOwnPropertyDescriptor(globalThis, name));
}
Object.defineProperty(globalThis, 'window', {
  configurable: true,
  writable: true,
  value: dom.window,
});
Object.defineProperty(globalThis, 'document', {
  configurable: true,
  writable: true,
  value: dom.window.document,
});

let root;
try {
  const container = document.getElementById('app');
  root = createRoot(container);

  // Without flushSync, render is deferred in concurrent React
  root.render(React.createElement('div', { id: 'status' }, 'deferred'));
  assert.equal(container.innerHTML, '', 'render without flushSync should not commit synchronously');

  // With flushSync, render is committed immediately
  flushSync(() => {
    root.render(React.createElement('div', { id: 'status' }, 'synchronous'));
  });
  assert.equal(container.innerHTML, '<div id="status">synchronous</div>', 'flushSync should commit DOM synchronously');

  // 4. flushSync around state updates commits component state changes synchronously to the DOM
  let setCounterState;
  function Counter() {
    const [count, setCount] = useState(0);
    setCounterState = setCount;
    return React.createElement('span', { id: 'count-val' }, `count:${count}`);
  }

  flushSync(() => {
    root.render(React.createElement(Counter));
  });
  assert.equal(container.innerHTML, '<span id="count-val">count:0</span>');

  // State update without flushSync does not commit synchronously
  setCounterState(1);
  assert.equal(container.innerHTML, '<span id="count-val">count:0</span>', 'state update without flushSync should be deferred');

  // State update wrapped in flushSync commits synchronously
  flushSync(() => {
    setCounterState(2);
  });
  assert.equal(container.innerHTML, '<span id="count-val">count:2</span>', 'state update with flushSync should commit synchronously');

  // 5. flushSync re-throws exceptions thrown by its callback
  assert.throws(
    () => {
      flushSync(() => {
        throw new Error('sync callback error');
      });
    },
    /sync callback error/
  );

  // 6. flushSync called without arguments returns undefined
  const noArgRet = flushSync();
  assert.equal(noArgRet, undefined, 'flushSync() without callback returns undefined');
} finally {
  if (root) {
    try {
      root.unmount();
    } catch {
      // ignore
    }
  }
  await new Promise((resolve) => setImmediate(resolve));
  dom.window.close();
  for (const [name, descriptor] of priorGlobals) {
    if (descriptor) {
      Object.defineProperty(globalThis, name, descriptor);
    } else {
      delete globalThis[name];
    }
  }
}

console.log('CONTRACT PASS: react-dom.flushSync verified');

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