基于jquery实现页面滚动时顶部导航显示隐藏

<script src="js/jquery/1.11.1/jquery.min.js"></script>

<div class="-title">这是顶部导航条</div>
<div class="margint"><p>滚动看效果</p><p>滚动看效果</p></div>

.-title {background:#e74c3c;color:white;font-size:24px;padding:5px;text-align:center;position: fixed;left:0;:0;width:100%;transition:  .5s;}
.hiddened{: -90px;}
.showed{:0;z-index: 9999;}

$(function(){ 
 var winHeight = $(document).scrollTop();
 
 $(window).scroll(function() {
  var scrollY = $(document).scrollTop();// 获取垂直滚动的距离，即滚动了多少
 
  if (scrollY > 550){ //如果滚动距离大于550px则隐藏，否则删除隐藏类
   $('.-title').addClass('hiddened');
  } 
  else {
   $('.-title').removeClass('hiddened');
  }
 
  if (scrollY > winHeight){ //如果没滚动到顶部，删除显示类，否则添加显示类
   $('.-title').removeClass('showed');
  } 
  else {
   $('.-title').addClass('showed');
  }    
 
  });
});