tsconfig.json

{
  "compilerOptions": {
    "target": "es2015",
    "module": "commonjs",
    "lib": ["esnext.asynciterable", "es2015", "dom"],
    "declaration": true,
    "resolveJsonModule": true,
    "declarationMap": true,
    "sourceMap": true,
    "outDir": "./build",
    "rootDir": "./src",
    "removeComments": true,
    "downlevelIteration": true,

    "strict": true,
    "noImplicitAny": true,
    "strictNullChecks": true,
    "strictFunctionTypes": true,
    "strictBindCallApply": true,
    "strictPropertyInitialization": true,
    "noImplicitThis": true,
    "alwaysStrict": true,

    "noUnusedLocals": true,
    "noUnusedParameters": true,
    "noImplicitReturns": true,
    "noFallthroughCasesInSwitch": true,

    "moduleResolution": "node",
    "baseUrl": "./src",
    "allowSyntheticDefaultImports": true,
    "esModuleInterop": true,

    "experimentalDecorators": true,
    "emitDecoratorMetadata": true
  }
}