react-is 19.2.8: isFragment

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-is.isFragment in pkg:npm/react-is@19.2.8
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:npm/react-is@19.2.8
Demonstrate these symbols/APIs:
  - react-is.isFragment
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:sha256:65a41fde3e3dcd54442866e63eaa1cc948b05b69432b3aa373d91c59c6909173","constraints":{"executionContext":"node"},"contract":["isFragment returns true for React 19 transitional elements whose type is React Fragment","isFragment returns false for bare React Fragment type symbol without an element wrapper","isFragment returns false for legacy react.element tagged elements not using transitional element tag","isFragment returns false for standard DOM elements, non-fragment elements, non-element objects, and primitives"],"goal":"verify react-is.isFragment in pkg:npm/react-is@19.2.8","kind":"HOW","packages":["pkg:npm/react-is@19.2.8"],"schemaVersion":1,"symbols":["react-is.isFragment"]},"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/react-is@19.2.8"],"schemaVersion":1,"subject":"pkg:npm/react-is@19.2.8","symbols":["react-is.isFragment"],"verifierAdapter":"node-typescript@1"}

{
  "name": "sample-react-is-fragment",
  "version": "1.0.0",
  "lockfileVersion": 3,
  "requires": true,
  "packages": {
    "": {
      "name": "sample-react-is-fragment",
      "version": "1.0.0",
      "license": "MIT-0",
      "dependencies": {
        "react-is": "19.2.8"
      }
    },
    "node_modules/react-is": {
      "version": "19.2.8",
      "resolved": "https://registry.npmjs.org/react-is/-/react-is-19.2.8.tgz",
      "integrity": "sha512-s5un28nYxKJw5gvUHyW5PCC28CvBqLu9r3cWgzHT4Vo/5fqqkFcdRYsGcKf50WMPpjjFZS5d76fn3YCo2njKwQ==",
      "license": "MIT"
    }
  }
}

{
  "name": "sample-react-is-fragment",
  "version": "1.0.0",
  "private": true,
  "description": "Clean-room verification of react-is.isFragment for React 19",
  "type": "module",
  "main": "src/index.mjs",
  "scripts": {
    "test": "node test/contract.mjs"
  },
  "dependencies": {
    "react-is": "19.2.8"
  },
  "license": "MIT-0"
}

{
  "schemaVersion": 1,
  "goal": "verify react-is.isFragment in pkg:npm/react-is@19.2.8",
  "kind": "HOW",
  "packages": [
    "pkg:npm/react-is@19.2.8"
  ],
  "symbols": [
    "react-is.isFragment"
  ],
  "constraints": {
    "executionContext": "node"
  },
  "runtimeConditions": {
    "ecosystem": "npm",
    "language": "javascript",
    "moduleSystem": "cjs",
    "packageManager": "npm@10.9.8",
    "runtime": "node@22.23.2"
  }
}

import { isFragment, Fragment, Element, typeOf } from 'react-is';

/**
 * Check if the given value is a React Fragment element.
 *
 * @param {*} value - The value to inspect.
 * @returns {boolean} True if the value is a React Fragment element.
 */
export function checkIsFragment(value) {
  return isFragment(value);
}

/**
 * Create a mock React 19 element with the specified type, props, and transitional element marker.
 *
 * @param {*} type - The element type (e.g. Fragment, string tag, component).
 * @param {object} [props={}] - Optional props object.
 * @returns {object} Mock React element object.
 */
export function createMockElement(type, props = {}) {
  return {
    $$typeof: Element,
    type,
    props,
    key: null,
    ref: null,
  };
}

/**
 * Create a mock React 19 Fragment element.
 *
 * @param {object} [props={}] - Optional props object.
 * @returns {object} Mock React Fragment element object.
 */
export function createMockFragment(props = {}) {
  return createMockElement(Fragment, props);
}

export { isFragment, Fragment, Element, typeOf };

import assert from 'node:assert/strict';
import {
  checkIsFragment,
  createMockElement,
  createMockFragment,
  isFragment,
  Fragment,
  Element,
  typeOf,
} from '../src/index.mjs';

// 1. isFragment returns true for React 19 transitional elements whose type is React Fragment
{
  const fragmentElement = createMockFragment({ children: ['Hello', 'World'] });
  assert.equal(
    isFragment(fragmentElement),
    true,
    'isFragment must return true for React 19 Fragment element'
  );
  assert.equal(
    checkIsFragment(fragmentElement),
    true,
    'checkIsFragment helper must return true for React 19 Fragment element'
  );

  const symbolForFragment = {
    $$typeof: Symbol.for('react.transitional.element'),
    type: Symbol.for('react.fragment'),
    props: {},
    key: null,
    ref: null,
  };
  assert.equal(
    isFragment(symbolForFragment),
    true,
    'isFragment must return true for element with global Symbol.for keys'
  );
}

// 2. isFragment returns false for bare React Fragment type symbol without an element wrapper
{
  assert.equal(
    isFragment(Fragment),
    false,
    'isFragment must return false for bare Fragment symbol'
  );
  assert.equal(
    checkIsFragment(Fragment),
    false,
    'checkIsFragment helper must return false for bare Fragment symbol'
  );
  assert.equal(
    isFragment(Symbol.for('react.fragment')),
    false,
    'isFragment must return false for Symbol.for("react.fragment")'
  );
}

// 3. isFragment returns false for legacy react.element tagged elements not using transitional element tag
{
  const legacyFragment = {
    $$typeof: Symbol.for('react.element'),
    type: Fragment,
    props: {},
    key: null,
    ref: null,
  };
  assert.equal(
    isFragment(legacyFragment),
    false,
    'isFragment in React 19 must return false for legacy react.element tag'
  );
  assert.equal(
    checkIsFragment(legacyFragment),
    false,
    'checkIsFragment helper must return false for legacy react.element tag'
  );
}

// 4. isFragment returns false for standard DOM elements, non-fragment elements, non-element objects, and primitives
{
  // Standard DOM element
  const domElement = createMockElement('div', { className: 'container' });
  assert.equal(isFragment(domElement), false, 'isFragment must return false for standard DOM element');

  // React elements with other types
  const suspenseElement = createMockElement(Symbol.for('react.suspense'), { fallback: null });
  assert.equal(isFragment(suspenseElement), false, 'isFragment must return false for suspense element');

  const plainFnElement = createMockElement(() => null);
  assert.equal(isFragment(plainFnElement), false, 'isFragment must return false for function component element');

  // Incomplete / non-element objects and primitives
  assert.equal(isFragment({}), false, 'isFragment must return false for plain empty object');
  assert.equal(isFragment({ $$typeof: Element }), false, 'isFragment must return false for element missing type');
  assert.equal(isFragment(null), false, 'isFragment must return false for null');
  assert.equal(isFragment(undefined), false, 'isFragment must return false for undefined');
  assert.equal(isFragment('<div></div>'), false, 'isFragment must return false for string');
  assert.equal(isFragment(42), false, 'isFragment must return false for number');
  assert.equal(isFragment(true), false, 'isFragment must return false for boolean');
  assert.equal(isFragment(Element), false, 'isFragment must return false for Element symbol');
}

console.log('Contract tests for react-is.isFragment (pkg:npm/react-is@19.2.8) passed successfully.');