tsconfig.json

{
  "compilerOptions": {
    "declaration": true,
    "importHelpers": true,
    "module": "commonjs",
    "outDir": "lib",
    "rootDir": "src",
    "strict": true,
    "target": "es2017",
    "allowSyntheticDefaultImports": true,
    "lib": [
      "ESNext.String"
    ]
  },
  "include": [
    "src/**/*"
  ]
}