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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 (__DEV__) {
      expect(ReactFreshRuntime.isLikelyComponentType(false)).toBe(false);
      expect(ReactFreshRuntime.isLikelyComponentType(null)).toBe(false);
      expect(ReactFreshRuntime.isLikelyComponentType('foo')).toBe(false);
      
      
      
      
      
      expect(ReactFreshRuntime.isLikelyComponentType(() => {})).toBe(false);
      expect(ReactFreshRuntime.isLikelyComponentType(function() {})).toBe(
        false,
      );
      expect(
        ReactFreshRuntime.isLikelyComponentType(function lightenColor() {}),
      ).toBe(false);
      const loadUser = () => {};
      expect(ReactFreshRuntime.isLikelyComponentType(loadUser)).toBe(false);
      const useStore = () => {};
      expect(ReactFreshRuntime.isLikelyComponentType(useStore)).toBe(false);
      expect(ReactFreshRuntime.isLikelyComponentType(useTheme)).toBe(false);
      
      let Button = () => {};
      expect(ReactFreshRuntime.isLikelyComponentType(Button)).toBe(true);
      expect(ReactFreshRuntime.isLikelyComponentType(Widget)).toBe(true);
      let anon = (() => () => {})();
      anon.displayName = 'Foo';
      expect(ReactFreshRuntime.isLikelyComponentType(anon)).toBe(true);
      
      class Btn extends React.Component {}