[CDN] Fix the UMD build

examples/cdn/README.md

@@ -22,6 +22,8 @@ which is great for prototyping. We discourage using this approach in production
 the client has to download the entire library, regardless of which components are actually used,
 affecting performance and bandwidth utilisation.
 
+[The live preview.](https://codesandbox.io/s/github/mui-org/material-ui/tree/master/examples/cdn)
+
 ## UMD releases
 
 We are providing two Universal Module Definition (UMD) files:

examples/cdn/package.json

@@ -0,0 +1,7 @@
+{
+  "name": "cdn",
+  "version": "3.0.0",
+  "private": true,
+  "dependencies": {},
+  "scripts": {}
+}

packages/material-ui-utils/src/componentPropType.js

@@ -1,4 +1,4 @@
-const ReactIs = require('react-is');
+import { isValidElementType } from 'react-is';
 
 /**
  * A factory that returns a propTypes validator that only accepts values that
@@ -25,7 +25,7 @@ function createComponentProp(isRequired) {
           `The ${location} \`${propName}\` is marked as required in \`${componentName}\`, ` +
           `but its value is \`${typeof prop}\`.`;
       }
-    } else if (!ReactIs.isValidElementType(prop)) {
+    } else if (!isValidElementType(prop)) {
       const preciseType = typeof prop;
       message =
         `Invalid ${location} \`${propName}\` of type \`${preciseType}\` ` +

packages/material-ui/scripts/rollup.config.js

@@ -21,6 +21,9 @@ const babelOptions = {
 const commonjsOptions = {
   ignoreGlobal: true,
   include: /node_modules/,
+  namedExports: {
+    '../../node_modules/react-is/index.js': ['isValidElementType'],
+  },
 };
 
 export default [