tsconfig.json

{
  "compilerOptions": {
    // Node 12 is the oldest runtime `engines` claims, and it predates
    // nullish coalescing and optional chaining. Emitting for es2019 makes tsc
    // downlevel those and reject any newer syntax at compile time, so the
    // published output cannot drift past what node 12 can parse. `lib` stays
    // at es2020 for the BigInt types; BigInt itself exists in node 12.
    "target": "es2019",
    "module": "commonjs",
    "allowJs": true,
    "declaration": true,
    "declarationMap": false,
    "rootDir": "./src",
    "outDir": "./dist",
    "resolveJsonModule": true,
    "sourceMap": true,
    "inlineSources": 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,

    "esModuleInterop": true,

    "skipLibCheck": true,
    "forceConsistentCasingInFileNames": true,

    "lib": ["es2020"]
  },

  "include": ["./src/**/*.ts"]
}