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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
}
export function performReactRefresh(): RefreshUpdate | null {
  if (!__DEV__) {
    throw new Error(
      'Unexpected call to React Refresh in a production environment.',
    );
  }
  if (pendingUpdates.length === 0) {
    return null;
  }
  if (isPerformingRefresh) {
    return null;
  }
  isPerformingRefresh = true;
  try {
    const staleFamilies = new Set();
    const updatedFamilies = new Set();
    const updates = pendingUpdates;
    pendingUpdates = [];
    updates.forEach(([family, nextType]) => {
      
      
      const prevType = family.current;
      updatedFamiliesByType.set(prevType, family);
      updatedFamiliesByType.set(nextType, family);
      family.current = nextType;
      
      if (canPreserveStateBetween(prevType, nextType)) {
        updatedFamilies.add(family);
      } else {