Repository: create-react-app
Issue: ReferenceError: Cannot access 'varName' before initialization
Labels: needs triage,issue: bug report

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### Describe the bug

Upgraded a react-app running React v17 to use react-scripts 4.0.0. First load in development returns an error that did not exist using 3.4.4

### Did you try recovering your dependencies?

Yes

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6.14.8

### Which terms did you search for in User Guide?

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Reference error

### Environment

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-->Environment Info:

  current version of create-react-app: 4.0.0
  running from C:\Users\MattCorner\AppData\Roaming\npm-cache\_npx\11504\node_modules\create-react-app

  System:
    OS: Windows 10 10.0.19041
    CPU: (12) x64 Intel(R) Core(TM) i7-9750H CPU @ 2.60GHz
  Binaries:
    Node: 14.8.0 - C:\Program Files\nodejs\node.EXE
    Yarn: Not Found
    npm: 6.14.8 - C:\Program Files\nodejs\npm.CMD
  Browsers:
    Chrome: Not Found
    Edge: Spartan (44.19041.423.0), Chromium (86.0.622.51)
    Internet Explorer: 11.0.19041.1
  npmPackages:
    react: Not Found
    react-dom: Not Found
    react-scripts: Not Found
  npmGlobalPackages:
    create-react-app: Not Found

### Steps to reproduce

This applications works fine in react-scripts 3.x.x. Based on the error message I suspect something to do with hot refresh.

The error is complaining about a custom hook called useSnackbar. This useSnackbar.js exports a SnackbarProvider and the useSnackbar hook. The useSnackbar hook is reexported through a hooks/index.js as so:

```
export {useSnackbar} from "./useSnackbar";
```
This hook is then use throughout the app.

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1. Start app in development
2. Microsoft edge loads and reports following error
3. ![image](https://user-images.githubusercontent.com/27866636/97465002-7e6f8480-1939-11eb-8b6a-839e054d6981.png)


### Expected behavior

Applications runs correctly in development using hot refresh.

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### Actual behavior

App errors on load.

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### Reproducible demo

Unable to reproduce outside of application.

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