Der Befehl "react-scripts" ist entweder falsch geschrieben oder code example

Example 1: 'react-scripts' n’est pas reconnu en tant que commande interne ou externe, un programme exécutable ou un fichier de commandes.

yarn upgrade
//or
npm update

Example 2: 'react-scripts' is not recognized as an internal or external command,

"scripts": {
  "build-css": "node-sass src/ -o src/",
  "build-js": "react-scripts build",
  "build": "npm run build-css && npm run build-js",
  "start-css": "npm run build-css && npm run build-css -- --watch --recursive",
  "start-js": "react-scripts start",
  "start": "npm-run-all -p start-css start-js",
  "test": "react-scripts test --env=jsdom",
  "eject": "react-scripts eject"
},