nilshartmann/upgrade-create-react-app-v4.md

## upgrade-create-react-app-v4.md

      
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              upgrade-create-react-app-v4.md
            
          
    Release Notes


...including Breaking Changes: https://github.com/facebook/create-react-app/releases/tag/v4.0.0

Upgrade react-scripts and dependencies:

yarn add --exact react-scripts@4.0.0
yarn add react react-dom
yarn add @types/react @types/react-dom
yarn add typescript
yarn add @testing-library/jest-dom @testing-library/react @testing-library/user-event @types/jest
Modify tsconfig.json


Add "noFallthroughCasesInSwitch": true to compilerOptions
background: facebook/create-react-app#9429

"Fix" resolution of external library


An included external library had both react and react-dom specified as dependency, causing problems with the Hooks API (https://reactjs.org/warnings/invalid-hook-call-warning.html#mismatching-versions-of-react-and-react-dom).
"Fixed" it by specifying a resolution policy in package.json:

"resolutions": {
    "lib-that-causes-trouble/react": "^17.0.1",
    "lib-that-causes-trouble/react-dom": "^17.0.1"
  }


of course "real" fix would be either upgrading the library to React 17 or (even better) if the lib would add React as peerDependency instead of dependency