Function registerStyles

src/index.ts:220–240

* Registers a set of style text. If it is registered too early, we will register it when the * window.load event is fired. * @param {ThemableArray} styleArray Array of IThemingInstruction objects to register. * @param {IStyleRecord} styleRecord May specify a style Element to update.

(styleArray: ThemableArray, styleRecord?: IStyleRecord)

 * @param {IStyleRecord} styleRecord May specify a style Element to update.
 */
function registerStyles(styleArray: ThemableArray, styleRecord?: IStyleRecord): void {
  const head: HTMLHeadElement = document.getElementsByTagName('head')[0];
  const styleElement: HTMLStyleElement = document.createElement('style');

  styleElement.type = 'text/css';
  styleElement.appendChild(document.createTextNode(resolveThemableArray(styleArray)));

  if (styleRecord) {
    head.replaceChild(styleElement, styleRecord.styleElement);
    styleRecord.styleElement = styleElement;
  } else {
    head.appendChild(styleElement);
  }

  if (!styleRecord) {
    _themeState.registeredStyles.push({
      styleElement: styleElement,
      themableStyle: styleArray
    });
  }
}

/**
 * Registers a set of style text, for IE 9 and below, which has a ~30 style element limit so we need