Using “npm run build” fails with “npm ERR! missing script: build”

First check you have .babelrc file in your root folder.

if you already have

Add this in your package.json file

"scripts": {
    "dev": "webpack --config=Scripts/config/webpack.dev.js --watch",
    "build": "webpack --config=Scripts/config/webpack.prod.js",
    "test": "echo \"Error: no test specified\" && exit 1"
  },