Authoritative brand checking library

Can be used without any dependency on React. Plausible replacement for
React.isValidElement.

packages/react-is/README.md

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+# `react-dom`
+
+This package serves as the entry point of the DOM-related rendering paths. It is intended to be paired with the isomorphic React, which will be shipped as `react` to npm.
+
+## Installation
+
+```sh
+npm install react react-dom
+```
+
+## Usage
+
+### In the browser
+
+```js
+var React = require('react');
+var ReactDOM = require('react-dom');
+
+class MyComponent extends React.Component {
+  render() {
+    return <div>Hello World</div>;
+  }
+}
+
+ReactDOM.render(<MyComponent />, node);
+```
+
+### On the server
+
+```js
+var React = require('react');
+var ReactDOMServer = require('react-dom/server');
+
+class MyComponent extends React.Component {
+  render() {
+    return <div>Hello World</div>;
+  }
+}
+
+ReactDOMServer.renderToString(<MyComponent />);
+```
+
+## API
+
+### `react-dom`
+
+- `findDOMNode`
+- `render`
+- `unmountComponentAtNode`
+
+### `react-dom/server`
+
+- `renderToString`
+- `renderToStaticMarkup`

packages/react-is/index.js

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+/**
+ * Copyright (c) 2014-present, Facebook, Inc.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+'use strict';
+
+var REACT_ELEMENT_TYPE;
+var REACT_COROUTINE_TYPE;
+var REACT_YIELD_TYPE;
+var REACT_PORTAL_TYPE;
+var REACT_FRAGMENT_TYPE;
+if (typeof Symbol === 'function' && Symbol.for) {
+  REACT_ELEMENT_TYPE = Symbol.for('react.element');
+  REACT_COROUTINE_TYPE = Symbol.for('react.coroutine');
+  REACT_YIELD_TYPE = Symbol.for('react.yield');
+  REACT_PORTAL_TYPE = Symbol.for('react.portal');
+  REACT_FRAGMENT_TYPE = Symbol.for('react.fragment');
+} else {
+  REACT_ELEMENT_TYPE = 0xeac7;
+  REACT_COROUTINE_TYPE = 0xeac8;
+  REACT_YIELD_TYPE = 0xeac9;
+  REACT_PORTAL_TYPE = 0xeaca;
+  REACT_FRAGMENT_TYPE = 0xeacb;
+}
+
+function is(object, type) {
+  return (
+    typeof object === 'object' && object !== null && object.$$typeof === type
+  );
+}
+
+module.exports = {
+  typeOf(object) {
+    switch (typeof object === 'object' && object !== null && object.$$typeof) {
+      case REACT_ELEMENT_TYPE:
+        return 'ReactElement';
+      case REACT_COROUTINE_TYPE:
+        return 'ReactCoroutine';
+      case REACT_YIELD_TYPE:
+        return 'ReactYield';
+      case REACT_PORTAL_TYPE:
+        return 'ReactPortal';
+      case REACT_FRAGMENT_TYPE:
+        return 'ReactFragment';
+      default:
+        return undefined;
+    }
+  },
+  isElement(object) {
+    return is(object, REACT_ELEMENT_TYPE);
+  },
+  isCoroutine(object) {
+    return is(object, REACT_COROUTINE_TYPE);
+  },
+  isYield(object) {
+    return is(object, REACT_YIELD_TYPE);
+  },
+  isPortal(object) {
+    return is(object, REACT_PORTAL_TYPE);
+  },
+  isFragment(object) {
+    return is(object, REACT_FRAGMENT_TYPE);
+  },
+};

packages/react-is/package.json

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+{
+  "name": "react-is",
+  "description": "Brand checking of React Elements.",
+  "keywords": [
+    "react"
+  ],
+  "version": "1.0.0",
+  "homepage": "https://reactjs.org/",
+  "bugs": "https://github.com/facebook/react/issues",
+  "license": "MIT",
+  "files": [
+    "index.js"
+  ],
+  "main": "index.js",
+  "repository": "facebook/react",
+  "engines": {
+    "node": ">=0.10.0"
+  }
+}