Cannot find namespace NodeJS after webpack upgrade

If you also have tsconfig.app.json in your working directory, try to add the attribute node to the types field. Like:

  {
  "extends": "../tsconfig.json",
  "compilerOptions": {
    "outDir": "../out-tsc/app",
    "module": "es6",
    "baseUrl": "",
    "types": ["node"] --> ADD THIS
  },
  "exclude": [
    "test.ts",
    "**/*.spec.ts"
  ]
}