tsconfig.json

{
  "include": [
    "src/**/*.ts"
  ],
  "compilerOptions": {
    "outDir": "lib",
    "target": "es2018",                          /* Specify ECMAScript target version: 'ES3' (default), 'ES5', 'ES2015', 'ES2016', 'ES2017','ES2018' or 'ESNEXT'. */
    "module": "commonjs",                     /* Specify module code generation: 'none', 'commonjs', 'amd', 'system', 'umd', 'es2015', or 'ESNext'. */
    "declaration": true,                   /* Generates corresponding '.d.ts' file. */
    "sourceMap": true,                     /* Generates corresponding '.map' file. */
    "strict": true,                           /* Enable all strict type-checking options. */
    "strictNullChecks": false,              /* Enable strict null checks. */
    "noUnusedLocals": true,                /* Report errors on unused locals. */
    "noUnusedParameters": true,            /* Report errors on unused parameters. */
    "noImplicitReturns": true,             /* Report error when not all code paths in function return a value. */
    "esModuleInterop": true               /* Enables emit interoperability between CommonJS and ES Modules via creation of namespace objects for all imports. Implies 'allowSyntheticDefaultImports'. */
  }
}