tsconfig.json

{
  "compilerOptions": {
    "outDir": "lib",
    "target": "es2016" /* Set the JavaScript language version for emitted JavaScript and include compatible library declarations. */,
    "module": "commonjs" /* Specify what module code is generated. */,
    "allowJs": true /* Allow JavaScript files to be a part of your program. Use the 'checkJS' option to get errors from these files. */,
    "esModuleInterop": true /* Emit additional JavaScript to ease support for importing CommonJS modules. This enables 'allowSyntheticDefaultImports' for type compatibility. */,
    "forceConsistentCasingInFileNames": true /* Ensure that casing is correct in imports. */,
    "strict": true /* Enable all strict type-checking options. */,
    "skipLibCheck": true /* Skip type checking all .d.ts files. */,
    "experimentalDecorators": true
  },
  "include": ["src/**/*"],
  "exclude": ["./src/**/*.spec.*"]
}