判断当前滚动高度并显示不同的东西（目录、二维码、评论框）。示例：https://munen.cc/tech/lazyload-Disqus.html

comment.jade

if theme.disqus
    a#comments
    #disqus_thread
    script.
        var disqus_run_count = 0;
        var disqus_shortname = '#{theme.disqus}';
        var disqus_identifier = '#{page.path}';
        var disqus_title = "#{page.title}";
        var disqus_url = '#{config.url}/#{page.path}';
        var disqus = {
          load : function disqus(){
            (function() {
                var dsq = document.createElement('script'); dsq.type = 'text/javascript'; dsq.async = true;
                dsq.src = '//' + disqus_shortname + '.disqus.com/embed.js';
                (document.getElementsByTagName('head')[0] || document.getElementsByTagName('body')[0]).appendChild(dsq);
            })();
            disqus_run_count ++;
          }
        }
        
    //script(id='dsq-count-scr' src='//#{theme.disqus}.disqus.com/count.js' async)

donate.css

#toc {
	font-size: 12px;
	font-weight: 300;
	line-height: 1.6;
	display: none;
	overflow: auto;
	width: 100%;
	max-width: 250px;
	max-height: 250px;
	margin: 60px auto 0;
	padding: 10px 40px 0;
	border-top: 1px solid #f2f2f2;
}
#toc ol {
	list-style: none;
}
.toc-list {
	padding-left: 10px;
}
#donate {
	display: none;
	width: 100%;
	max-width: 450px;
	margin: 60px auto 0;
}
.fadeInDown {
	-webkit-animation-name: fadeInDown;
	animation-name: fadeInDown;
}
.animated {
	-webkit-animation-duration: 1s;
	animation-duration: 1s;
	-webkit-animation-fill-mode: both;
	animation-fill-mode: both;
}

donate.js

$(window).load(function() {
  var target = document.getElementsByClassName('post')[0].scrollHeight;
  var current = 0;
  if (target < $(window).height()) {
    $("#donate").css("display", "block");
    disqus.load();
  } else {
    $(window).scroll(function() {
      current = $(window).scrollTop();
      if (current > target - $(window).height() && current < target) {
        $("#toc").hide();
        $("#donate").css("display", "block");
        if (disqus_run_count == 0) {
          disqus.load();
        }
      } else {
        $("#donate").hide();
        $("#toc").show();
      }
    })
  }
})

sidebar.jade

if is_post()
  if !page.hideToc
    #toc.animated.fadeInDown
      != toc(page.content, {class: 'toc-list'})
  if !page.hideDonate
    img#donate.animated.fadeInDown(src="/images/donate.png")