With `esModuleInterop: true` and `module: "commonjs"`, default-importing a module that has the `__esModule: true` marker behaves differently from default-importing one without it. What does the emitted `__importDefault` helper do, and why does the marker matter?
// __importDefault roughly:
function __importDefault(mod) {
return (mod && mod.__esModule) ? mod : { default: mod };
}