Function register

src/index.ts:584–615

(
  serviceOrOpts: Service | RegisterOptions | undefined
)

 */
export function register(service: Service): Service;
export function register(
  serviceOrOpts: Service | RegisterOptions | undefined
): Service {
  // Is this a Service or a RegisterOptions?
  let service = serviceOrOpts as Service;
  if (!(serviceOrOpts as Service)?.[TS_NODE_SERVICE_BRAND]) {
    // Not a service; is options
    service = create((serviceOrOpts ?? {}) as RegisterOptions);
  }

  const originalJsHandler = require.extensions['.js'];

  // Expose registered instance globally.
  process[REGISTER_INSTANCE] = service;

  // Register the extensions.
  registerExtensions(
    service.options.preferTsExts,
    service.extensions.compiled,
    service,
    originalJsHandler
  );

  installCommonjsResolveHooksIfNecessary(service);

  // Require specified modules before start-up.
  (Module as ModuleConstructorWithInternals)._preloadModules(
    service.options.require
  );

  return service;
}

/**
 * Create TypeScript compiler instance.