Next.js

Uses [email protected] judging from package-lock.json.

cd next
npm install
npm run dev

Open http://localhost:3000 with your browser and read the steps to reproduce.

This warning appears in the devtools' console:

Warning: Each child in a list should have a unique "key" prop. See https://reactjs.org/link/warning-keys for more information.

React (using Create React App)

Uses [email protected] judging from package-lock.json.

cd create-react-app
npm install
npm run start

Open http://localhost:3000 with your browser and read the steps to reproduce.

There is no warning in the devtools' console.