Function preinitStyle

packages/react-dom-bindings/src/client/ReactFiberConfigDOM.js:4830–4906

(
  href: string,
  precedence: ?string,
  options?: ?PreinitStyleOptions,
)

}

function preinitStyle(
  href: string,
  precedence: ?string,
  options?: ?PreinitStyleOptions,
) {
  previousDispatcher.S(/* preinitStyle */ href, precedence, options);

  const ownerDocument = getGlobalDocument();
  if (ownerDocument && href) {
    const styles = getResourcesFromRoot(ownerDocument).hoistableStyles;

    const key = getStyleKey(href);
    precedence = precedence || 'default';

    // Check if this resource already exists
    let resource = styles.get(key);
    if (resource) {
      // We can early return. The resource exists and there is nothing
      // more to do
      return;
    }

    const state = {
      loading: NotLoaded,
      preload: null,
    };

    // Attempt to hydrate instance from DOM
    let instance: null | Instance = ownerDocument.querySelector(
      getStylesheetSelectorFromKey(key),
    );
    if (instance) {
      state.loading = Loaded | Inserted;
    } else {
      // Construct a new instance and insert it
      const stylesheetProps = Object.assign(
        ({
          rel: 'stylesheet',
          href,
          'data-precedence': precedence,
        }: StylesheetProps),
        options,
      );
      const preloadProps = preloadPropsMap.get(key);
      if (preloadProps) {
        adoptPreloadPropsForStylesheet(stylesheetProps, preloadProps);
      }
      const link = (instance = ownerDocument.createElement('link'));
      markNodeAsHoistable(link);
      setInitialProperties(link, 'link', stylesheetProps);

      (link: any)._p = new Promise((resolve, reject) => {
        link.onload = resolve;
        link.onerror = reject;
      });
      link.addEventListener('load', () => {
        state.loading |= Loaded;
      });