react 19.2.8: useEffect

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.useEffect in pkg:npm/react@19.2.8
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:npm/react@19.2.8
Demonstrate these symbols/APIs:
  - react.useEffect

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.

{"case":{"caseId":"case:sha256:2b6a8f7ce6f5ffd2466facba62575a958115792146fbe0f6caf91ae691ef794c","contract":["react package.json declares export mappings for client and react-server entries at version 19.2.8","react exports useEffect as a function on the default client runtime interface","react useEffect throws a TypeError when invoked outside an active component render dispatcher","react useEffect delegates setup callback and dependencies to the active ReactCurrentDispatcher","react useEffect supports empty dependency arrays and omitted dependencies passing them to the dispatcher","react react-server entry explicitly omits useEffect export in server component environments"],"goal":"verify react.useEffect in pkg:npm/react@19.2.8","kind":"HOW","packages":["pkg:npm/react@19.2.8"],"schemaVersion":1,"symbols":["react.useEffect"]},"contractCommand":["node","test/contract.mjs"],"environment":{"arch":"x64","distro":"ubuntu","ecosystem":"npm","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@19.2.8"],"schemaVersion":1,"subject":"pkg:npm/react@19.2.8","symbols":["react.useEffect"],"verifierAdapter":"node-typescript@1"}

{
  "name": "sample-react-use-effect",
  "version": "1.0.0",
  "lockfileVersion": 3,
  "requires": true,
  "packages": {
    "": {
      "name": "sample-react-use-effect",
      "version": "1.0.0",
      "license": "MIT-0",
      "dependencies": {
        "react": "19.2.8"
      }
    },
    "node_modules/react": {
      "version": "19.2.8",
      "resolved": "https://registry.npmjs.org/react/-/react-19.2.8.tgz",
      "integrity": "sha512-PWaYA1L/q9u2u7xYQi+Y3L3Yfnie7XyLeaJICV1MGD6LprsBxcAqGjYyr0eY3p+QdsA+x/Irkt4Qif8D63+Sbw==",
      "license": "MIT",
      "engines": {
        "node": ">=0.10.0"
      }
    }
  }
}

{
  "name": "sample-react-use-effect",
  "version": "1.0.0",
  "type": "module",
  "private": true,
  "license": "MIT-0",
  "dependencies": {
    "react": "19.2.8"
  }
}

{
  "schemaVersion": 1,
  "goal": "verify react.useEffect in pkg:npm/react@19.2.8",
  "kind": "HOW",
  "packages": [
    "pkg:npm/react@19.2.8"
  ],
  "symbols": [
    "react.useEffect"
  ]
}

import assert from 'node:assert/strict';
import fs from 'node:fs';
import path from 'node:path';
import { createRequire } from 'node:module';
import React from 'react';

const require = createRequire(import.meta.url);

// Contract 1: react package.json declares export mappings for client and react-server entries at version 19.2.8
{
  const pkgJsonPath = require.resolve('react/package.json');
  assert.ok(fs.existsSync(pkgJsonPath));
  const pkgJson = JSON.parse(fs.readFileSync(pkgJsonPath, 'utf8'));
  assert.strictEqual(pkgJson.name, 'react');
  assert.strictEqual(pkgJson.version, '19.2.8');
  assert.strictEqual(pkgJson.exports['.']['default'], './index.js');
  assert.strictEqual(pkgJson.exports['.']['react-server'], './react.react-server.js');
}

// Contract 2: react exports useEffect as a function on the default client runtime interface
{
  assert.strictEqual(typeof React.useEffect, 'function');
  assert.strictEqual(React.version, '19.2.8');
}

// Contract 3: react useEffect throws a TypeError when invoked outside an active component render dispatcher
{
  const internals = React.__CLIENT_INTERNALS_DO_NOT_USE_OR_WARN_USERS_THEY_CANNOT_UPGRADE;
  assert.ok(internals && typeof internals === 'object');
  assert.strictEqual(internals.H, null);

  assert.throws(
    () => {
      React.useEffect(() => {});
    },
    {
      name: 'TypeError'
    }
  );
}

// Contract 4: react useEffect delegates setup callback and dependencies to the active ReactCurrentDispatcher
{
  const internals = React.__CLIENT_INTERNALS_DO_NOT_USE_OR_WARN_USERS_THEY_CANNOT_UPGRADE;
  let receivedCall = null;
  const mockReturn = { __registered: true };

  internals.H = {
    useEffect(create, deps) {
      receivedCall = { create, deps };
      return mockReturn;
    }
  };

  try {
    const effectCallback = () => {};
    const deps = ['item1', 42, true];
    const result = React.useEffect(effectCallback, deps);

    assert.strictEqual(result, mockReturn);
    assert.ok(receivedCall !== null);
    assert.strictEqual(receivedCall.create, effectCallback);
    assert.strictEqual(receivedCall.deps, deps);
  } finally {
    internals.H = null;
  }
}

// Contract 5: react useEffect supports empty dependency arrays and omitted dependencies passing them to the dispatcher
{
  const internals = React.__CLIENT_INTERNALS_DO_NOT_USE_OR_WARN_USERS_THEY_CANNOT_UPGRADE;
  let receivedCalls = [];

  internals.H = {
    useEffect(create, deps) {
      receivedCalls.push({ create, deps });
    }
  };

  try {
    const fn1 = () => {};
    const fn2 = () => {};

    // Without dependencies argument
    React.useEffect(fn1);
    assert.strictEqual(receivedCalls.length, 1);
    assert.strictEqual(receivedCalls[0].create, fn1);
    assert.strictEqual(receivedCalls[0].deps, undefined);

    // With empty dependencies array
    React.useEffect(fn2, []);
    assert.strictEqual(receivedCalls.length, 2);
    assert.strictEqual(receivedCalls[1].create, fn2);
    assert.deepStrictEqual(receivedCalls[1].deps, []);
  } finally {
    internals.H = null;
  }
}

// Contract 6: react react-server entry explicitly omits useEffect export in server component environments
{
  const pkgJsonPath = require.resolve('react/package.json');
  const pkgDir = path.dirname(pkgJsonPath);
  const pkgJson = JSON.parse(fs.readFileSync(pkgJsonPath, 'utf8'));
  const reactServerEntry = path.join(pkgDir, pkgJson.exports['.']['react-server']);
  const reactServer = require(reactServerEntry);

  assert.strictEqual(reactServer.version, '19.2.8');
  assert.strictEqual(reactServer.useEffect, undefined);
}

console.log('All react.useEffect contract tests passed.');