获取上一篇文章和下一篇文章的标题

问：

我正在努力从默认导航开始向 Blogger 添加下一个和上一个导航按钮，并向其添加帖子标题

我尝试使用 Blogger 提要获取帖子的标题，但由于某种原因，它说没有定义回调函数

这是代码

 <a expr:href='data:olderPageUrl'>
                      <div class='older-post'>
                        <span class='pager_icon'><svg class='line' viewBox='0 0 24 24' xmlns='http://www.w3.org/2000/svg'><polyline points='15 18 9 12 15 6'/></svg></span>
                        <span>prev</span>
                        <a class='blog-pager-older-link' expr:href='data:olderPageUrl' expr:id='data:widget.instanceId + &quot;_blog-pager-older-link&quot;' expr:title='data:olderPageTitle'><span class='older-text'><data:olderPageTitle/></span></a>
                      </div>
                    </a>

                    <a expr:href='data:newerPageUrl'>
                      <div class='newer-post'>
                        <span class='pager_icon'><svg class='line' viewBox='0 0 24 24' xmlns='http://www.w3.org/2000/svg'><polyline points='9 18 15 12 9 6'/></svg></span>
                        <span>next</span>
                        <a class='blog-pager-newer-link' expr:href='data:newerPageUrl' expr:id='data:widget.instanceId + &quot;_blog-pager-newer-link&quot;' expr:title='data:newerPageTitle'><span class='newer-text'><data:newerPageTitle/></span></a>
                      </div>
                    </a>

 /*********** Between Posts Navigation Starts ************/
  var olderLink = document.getElementById('Blog1_blog-pager-older-link');
  if (olderLink) {
    getPageTitle(olderLink, setOlderPageTitle);
    function setOlderPageTitle(data){
      setPageTitle(data, olderLink, '', '')
    };
  }
  var newerLink = document.getElementById('Blog1_blog-pager-newer-link');
  if (newerLink) {
    getPageTitle(newerLink, setNewerPageTitle);
    function setNewerPageTitle(data){
      setPageTitle(data, newerLink, '', '')
    };
  }
  // set the page title from feed data
  function setPageTitle(data, pageLink, prefix, suffix) {
    if (data.feed.entry) {
      if (data.feed.entry.length > 0) {
        var title = data.feed.entry[0].title.$t;
      }
    }
    if (title) {
      pageLink.innerHTML = prefix + title + suffix;
    }
  }
  // get entry data from the feed
  function getPageTitle(pageLink, callback) {
      var pathname = pageLink.getAttribute('href').replace(location.protocol + '//' + location.hostname, '');
      var script = document.createElement('script');
      script.src = '/feeds/posts/summary?alt=json-in-script&max-results=1&redirect=false&path='+pathname+'&callback='+callback.name+'';
   var headTg =  document.getElementsByTagName('head')[0];
      document.body.appendChild(script);
  }
 /*********** Between Posts Navigation End ************/