即使img原本就有style也能解决

 formatImg (html) {
    var newContent = html.replace(/<img[^>]*>/gi, (match) => {
      let processed=null;
      if(!match.match(/style=\"(.*)\"/gi)){
        processed=match.replace(/\<img/g, '<img style="width:100%;height:auto;display:block"');
      }else{
        processed = match.replace(/style=\"(.*)\"/gi, 'style="width:100%;height:auto;display:block"');
      }
      return processed;
    });
    return newContent;
  }