function metroRequire()

in packages/metro-runtime/src/polyfills/require.js [152:194]
37 lines of code
10 McCabe index (conditional complexity)

function metroRequire(moduleId: ModuleID | VerboseModuleNameForDev): Exports {
  if (__DEV__ && typeof moduleId === 'string') {
    const verboseName = moduleId;
    moduleId = verboseNamesToModuleIds[verboseName];
    if (moduleId == null) {
      throw new Error(`Unknown named module: "${verboseName}"`);
    } else {
      console.warn(
        `Requiring module "${verboseName}" by name is only supported for ` +
          'debugging purposes and will BREAK IN PRODUCTION!',
      );
    }
  }

  //$FlowFixMe: at this point we know that moduleId is a number
  const moduleIdReallyIsNumber: number = moduleId;

  if (__DEV__) {
    const initializingIndex = initializingModuleIds.indexOf(
      moduleIdReallyIsNumber,
    );
    if (initializingIndex !== -1) {
      const cycle = initializingModuleIds
        .slice(initializingIndex)
        .map((id: number) =>
          modules[id] ? modules[id].verboseName : '[unknown]',
        );
      // We want to show A -> B -> A:
      cycle.push(cycle[0]);
      console.warn(
        `Require cycle: ${cycle.join(' -> ')}\n\n` +
          'Require cycles are allowed, but can result in uninitialized values. ' +
          'Consider refactoring to remove the need for a cycle.',
      );
    }
  }

  const module = modules[moduleIdReallyIsNumber];

  return module && module.isInitialized
    ? module.publicModule.exports
    : guardedLoadModule(moduleIdReallyIsNumber, module);
}