react-is 19.2.8: isElement

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.isElement 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.isElement

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:c704219bd3933b9b136a5e26386ed097fdf118447735b842e5d930ee8a85125f","contract":["isElement returns true for React elements bearing Symbol.for('react.transitional.element')","isElement returns false for legacy React elements bearing Symbol.for('react.element')","isElement returns false for plain objects, null, undefined, and primitive types"],"goal":"verify react-is.isElement in pkg:npm/react-is@19.2.8","kind":"HOW","packages":["pkg:npm/react-is@19.2.8"],"schemaVersion":1,"symbols":["react-is.isElement"]},"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-is@19.2.8"],"schemaVersion":1,"subject":"pkg:npm/react-is@19.2.8","symbols":["react-is.isElement"],"verifierAdapter":"node-typescript@1"}

{
  "name": "sample-react-is-element",
  "version": "1.0.0",
  "lockfileVersion": 3,
  "requires": true,
  "packages": {
    "": {
      "name": "sample-react-is-element",
      "version": "1.0.0",
      "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-element",
  "version": "1.0.0",
  "private": true,
  "description": "Verification of react-is isElement in React 19",
  "type": "module",
  "main": "src/index.js",
  "dependencies": {
    "react-is": "19.2.8"
  }
}

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

import { isElement, Element } from 'react-is';

/**
 * Check if the given value is a valid React element.
 * In React 19, valid React elements have $$typeof matching Symbol.for('react.transitional.element').
 *
 * @param {*} value - The value to inspect.
 * @returns {boolean} True if the value is a valid React element.
 */
export function checkIsElement(value) {
  return isElement(value);
}

export { isElement, Element };

import assert from 'node:assert/strict';
import { checkIsElement, isElement, Element } from '../src/index.js';

// 1. Symbol and function export verification
assert.equal(typeof isElement, 'function', 'isElement must be a function');
assert.equal(typeof checkIsElement, 'function', 'checkIsElement must be a function');
assert.equal(typeof Element, 'symbol', 'Element must be a symbol');
assert.equal(
  Element,
  Symbol.for('react.transitional.element'),
  'Element must equal Symbol.for("react.transitional.element") in React 19'
);

// 2. React 19 Element identification
const validElement = {
  $$typeof: Element,
  type: 'div',
  props: { className: 'container' },
  key: null,
  ref: null,
};
assert.equal(isElement(validElement), true, 'isElement must return true for valid React 19 element');
assert.equal(checkIsElement(validElement), true, 'checkIsElement must return true for valid React 19 element');

// 3. Rejection of pre-React 19 element symbol
const legacyElement = {
  $$typeof: Symbol.for('react.element'),
  type: 'div',
  props: {},
  key: null,
  ref: null,
};
assert.equal(isElement(legacyElement), false, 'isElement must return false for pre-React 19 react.element symbol');
assert.equal(checkIsElement(legacyElement), false, 'checkIsElement must return false for pre-React 19 react.element symbol');

// 4. Rejection of non-element objects and primitives
assert.equal(isElement({}), false, 'isElement must return false for empty plain object');
assert.equal(isElement({ type: 'div' }), false, 'isElement must return false for plain object without $$typeof');
assert.equal(isElement(null), false, 'isElement must return false for null');
assert.equal(isElement(undefined), false, 'isElement must return false for undefined');
assert.equal(isElement('div'), false, 'isElement must return false for string');
assert.equal(isElement(123), false, 'isElement must return false for number');
assert.equal(isElement(true), false, 'isElement must return false for boolean');
assert.equal(isElement([]), false, 'isElement must return false for array');
assert.equal(isElement(() => {}), false, 'isElement must return false for function');

console.log('Contract tests passed successfully.');