Function render

packages/react-native-renderer/src/ReactFabric.js:108–172

(
  element: Element<ElementType>,
  containerTag: number,
  callback: ?() => void,
  concurrentRoot: ?boolean,
  options: ?RenderRootOptions,
)

}

function render(
  element: Element<ElementType>,
  containerTag: number,
  callback: ?() => void,
  concurrentRoot: ?boolean,
  options: ?RenderRootOptions,
): ?ElementRef<ElementType> {
  if (disableLegacyMode && !concurrentRoot) {
    throw new Error('render: Unsupported Legacy Mode API.');
  }

  let root = roots.get(containerTag);

  if (!root) {
    // TODO: these defaults are for backwards compatibility.
    // Once RN implements these options internally,
    // we can remove the defaults and ReactFiberErrorDialog.
    let onUncaughtError = nativeOnUncaughtError;
    let onCaughtError = nativeOnCaughtError;
    let onRecoverableError = defaultOnRecoverableError;

    if (options && options.onUncaughtError !== undefined) {
      onUncaughtError = options.onUncaughtError;
    }
    if (options && options.onCaughtError !== undefined) {
      onCaughtError = options.onCaughtError;
    }
    if (options && options.onRecoverableError !== undefined) {
      onRecoverableError = options.onRecoverableError;
    }
    let onDefaultTransitionIndicator = nativeOnDefaultTransitionIndicator;
    if (enableDefaultTransitionIndicator) {
      if (options && options.onDefaultTransitionIndicator !== undefined) {
        onDefaultTransitionIndicator = options.onDefaultTransitionIndicator;
      }
    }

    const publicRootInstance = createPublicRootInstance(containerTag);
    const rootInstance = {
      publicInstance: publicRootInstance,
      containerTag,
    };

    // TODO (bvaughn): If we decide to keep the wrapper component,
    // We could create a wrapper for containerTag as well to reduce special casing.
    root = createContainer(
      rootInstance,
      concurrentRoot ? ConcurrentRoot : LegacyRoot,
      null,
      false,
      null,
      '',
      onUncaughtError,
      onCaughtError,
      onRecoverableError,
      onDefaultTransitionIndicator,
      null,
    );