How to disable source maps for React JS Application

just remove &&

"scripts": {    
    "start": "react-scripts start",
    "build": "GENERATE_SOURCEMAP=false react-scripts build",
    "test": "react-scripts test --env=jsdom",
    "eject": "react-scripts eject"
  }

You have to create a .env file in your root directory (same folder as package.json) and set GENERATE_SOURCEMAP=false on a single line.

for additional configurations, you may refer to the documentation here: https://facebook.github.io/create-react-app/docs/advanced-configuration