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**Do you want to request a *feature* or report a *bug*?**

feature

**What is the current behavior?**

When `react-dom` is loaded from CDN like `<script src="https://cdn.jsdelivr.net/npm/react-dom@16.12.0/umd/react-dom.development.js"></script>`, `react-refresh` failed to inject hook into devtools.

I've created a related issue here: https://github.com/pmmmwh/react-refresh-webpack-plugin/issues/13

We should find a way to invoke `injectIntoGlobalHook` function from `react-refresh/runtime`, however this file is in cjs format so we cannot currently do this in a simple way.

**What is the expected behavior?**

I'd like `react-refresh` to publish runtime as a umd bundle so we can reference it from CDN and put it before `react-dom`'s `<script>` element, then invoke `injectIntoGlobalHook` in the right place.

**Which versions of React, and which browser / OS are affected by this issue? Did this work in previous versions of React?**

- `react-dom`: 16.12.0
- `react-refresh`: 0.7.0
if (type.prototype.isReactComponent) {
            
            return true;
          }
          const ownNames = Object.getOwnPropertyNames(type.prototype);
          if (ownNames.length > 1 || ownNames[0] !== 'constructor') {
            
            return false;
          }
          
          if (type.prototype.__proto__ !== Object.prototype) {
            
            return false;
          }
          
          
        }
        
        const name = type.name || type.displayName;
        return typeof name === 'string' && /^[A-Z]/.test(name);
      }
      case 'object': {
        if (type != null) {
          switch (type.$$typeof) {