How to use the react-docgen.defaultHandlers.concat function in react-docgen

const stylesRegexp = /export const styles.*[\r\n](.*[\r\n])*};[\r\n][\r\n]/;
    const styleRegexp = /\/\* (.*) \*\/[\r\n]\s*(\w*)/g;
    // Extract the styles section from the source
    const stylesSrc = stylesRegexp.exec(styleSrc);

    if (stylesSrc) {
      // Extract individual classes and descriptions
      stylesSrc[0].replace(styleRegexp, (match, desc, key) => {
        styles.descriptions[key] = desc;
      });
    }
  }

  let reactAPI;
  try {
    reactAPI = docgenParse(src, null, defaultHandlers.concat(muiDefaultPropsHandler), {
      filename: componentObject.filename,
    });
  } catch (err) {
    console.log('Error parsing src for', componentObject.filename);
    throw err;
  }

  reactAPI.name = name;
  reactAPI.styles = styles;
  reactAPI.pagesMarkdown = pagesMarkdown;
  reactAPI.src = src;
  reactAPI.spread = spread;
  reactAPI.EOL = getLineFeed(src);

  const testInfo = await parseTest(componentObject.filename);
  // no Object.assign to visually check for collisions

handlers: componentPath =>
    defaultHandlers.concat(dnHandler.createDisplayNameHandler(componentPath))
};

module.exports = rootPath => {
  return defaultHandlers.concat([markdownHandler(rootPath)]);
};