@types/react 19.2.18: useOptimistic

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 useOptimistic in pkg:npm/%40types/react@19.2.18
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:npm/%40types/react@19.2.18
Demonstrate these symbols/APIs:
  - useOptimistic
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.

{"case":{"caseId":"case:sha256:814079288a08e5ab0442fe94e37a30c838a4d20001140919b03dea05cfecdabc","constraints":{"executionContext":"node"},"contract":["@types/react package.json declares type definitions entry point index.d.ts and version 19.2.18","@types/react index.d.ts exports useOptimistic function declaration accepting passthrough state","@types/react useOptimistic single-argument overload returns tuple with state and action dispatcher accepting state or updater function","@types/react index.d.ts exports useOptimistic function declaration accepting passthrough state and reducer function","@types/react useOptimistic two-argument overload returns tuple with state and action dispatcher","@types/react ts5.0/index.d.ts provides compatible useOptimistic declarations for TypeScript 5.0 and earlier"],"goal":"verify useOptimistic in pkg:npm/%40types/react@19.2.18","kind":"HOW","packages":["pkg:npm/%40types/react@19.2.18"],"schemaVersion":1,"symbols":["useOptimistic"]},"contractCommand":["node","test/contract.mjs"],"environment":{"arch":"x64","distro":"ubuntu","ecosystem":"npm","executionContext":"node","language":"javascript","libc":"glibc","libcVersion":"2.39","moduleSystem":"cjs","os":"linux","osVersionBucket":"24","packageManager":"npm","packageManagerVersion":"10.9.8","runtime":"node","runtimeVersion":"22.23.2","schemaVersion":1},"license":"MIT-0","packages":["pkg:npm/%40types/react@19.2.18"],"schemaVersion":1,"subject":"pkg:npm/%40types/react@19.2.18","symbols":["useOptimistic"],"verifierAdapter":"node-typescript@1"}

{
  "name": "sample-types-react",
  "version": "1.0.0",
  "lockfileVersion": 3,
  "requires": true,
  "packages": {
    "": {
      "name": "sample-types-react",
      "version": "1.0.0",
      "license": "MIT-0",
      "dependencies": {
        "@types/react": "19.2.18"
      }
    },
    "node_modules/@types/react": {
      "version": "19.2.18",
      "resolved": "https://registry.npmjs.org/@types/react/-/react-19.2.18.tgz",
      "integrity": "sha512-AnzbBERsrLKtk2XSfTbYRLjQPdy116Sty4q+T+Bp3IC4l6jNBvreVPAHmpq9qhXQM7CXZPjLVmGMw9sy+hxQ3w==",
      "license": "MIT",
      "dependencies": {
        "csstype": "^3.2.2"
      }
    },
    "node_modules/csstype": {
      "version": "3.2.3",
      "resolved": "https://registry.npmjs.org/csstype/-/csstype-3.2.3.tgz",
      "integrity": "sha512-z1HGKcYy2xA8AGQfwrn0PAy+PB7X/GSj3UVJW9qKyn43xWa+gl5nXmU4qqLMRzWVLFC8KusUX8T/0kCiOYpAIQ==",
      "license": "MIT"
    }
  }
}

{
  "name": "sample-types-react",
  "version": "1.0.0",
  "type": "module",
  "private": true,
  "license": "MIT-0",
  "dependencies": {
    "@types/react": "19.2.18"
  }
}

{
  "schemaVersion": 1,
  "goal": "verify useOptimistic in pkg:npm/%40types/react@19.2.18",
  "kind": "HOW",
  "packages": [
    "pkg:npm/%40types/react@19.2.18"
  ],
  "symbols": [
    "useOptimistic"
  ],
  "constraints": {
    "executionContext": "node"
  },
  "runtimeConditions": {
    "ecosystem": "npm",
    "language": "javascript",
    "moduleSystem": "cjs",
    "packageManager": "npm@10.9.8",
    "runtime": "node@22.23.2"
  }
}

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

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

// 1. @types/react package.json declares type definitions entry point index.d.ts and version 19.2.18
const pkgJsonPath = require.resolve('@types/react/package.json');
assert.ok(fs.existsSync(pkgJsonPath));
const pkgJson = JSON.parse(fs.readFileSync(pkgJsonPath, 'utf8'));
assert.equal(pkgJson.name, '@types/react');
assert.equal(pkgJson.version, '19.2.18');
assert.equal(pkgJson.types, 'index.d.ts');
assert.equal(pkgJson.exports['.'].types.default, './index.d.ts');

const pkgDir = path.dirname(pkgJsonPath);

// 2. @types/react index.d.ts exports useOptimistic function declaration accepting passthrough state
const dtsPath = path.join(pkgDir, 'index.d.ts');
assert.ok(fs.existsSync(dtsPath));
const dtsContent = fs.readFileSync(dtsPath, 'utf8');

assert.ok(dtsContent.includes('export function useOptimistic<State>('));
assert.ok(dtsContent.includes('passthrough: State,'));

// 3. @types/react useOptimistic single-argument overload returns tuple with state and action dispatcher accepting state or updater function
assert.ok(dtsContent.includes('): [State, (action: State | ((pendingState: State) => State)) => void];'));

// 4. @types/react index.d.ts exports useOptimistic function declaration accepting passthrough state and reducer function
assert.ok(dtsContent.includes('export function useOptimistic<State, Action>('));
assert.ok(dtsContent.includes('reducer: (state: State, action: Action) => State,'));

// 5. @types/react useOptimistic two-argument overload returns tuple with state and action dispatcher
assert.ok(dtsContent.includes('): [State, (action: Action) => void];'));

// 6. @types/react ts5.0/index.d.ts provides compatible useOptimistic declarations for TypeScript 5.0 and earlier
const ts5DtsPath = path.join(pkgDir, 'ts5.0', 'index.d.ts');
assert.ok(fs.existsSync(ts5DtsPath));
const ts5DtsContent = fs.readFileSync(ts5DtsPath, 'utf8');
assert.ok(ts5DtsContent.includes('export function useOptimistic<State>('));
assert.ok(ts5DtsContent.includes('export function useOptimistic<State, Action>('));

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