js滚动到顶部后浮空顶部
第一种方法：

<script type="text/javascript">
  function menuFixed(id) {
    var obj = document.getElementById(id);
    var _getHeight = obj.offsetTop;
    window.onscroll = function () {
      changePos(id, _getHeight);
    }
  }
  function changePos(id, height) {
    var obj = document.getElementById(id);
    var scrollTop = document.documentElement.scrollTop || document.body.scrollTop;
    if (scrollTop < height) {
    obj.style.position = 'relative';
    } else {
      obj.style.position = 'fixed';
	  obj.style.top = '5px';/*这里是你浮空后跟顶部的距离*/	
    }
  }
  window.onload = function () {
    menuFixed('home_ss_r');/*这里是你浮空的id名称*/
  }
</script>

第二种方法：

<style>.fiexd_top0 .home_ss_r{/*这里是你浮空的class名称*/position:fiexd;top:0;/*这里是你浮空后跟顶部的距离*/}</style>
<script>
			var header = document.getElementsByClassName('home_ss_r')[0];/*这里是你浮空的class名称*/
			var body = document.body;
			window.onscroll = function() {
				var scrollTop = document.documentElement.scrollTop || document.body.scrollTop;
				console.log(scrollTop);
				if (scrollTop > 400) {/*控制滚动多少像素*/
					 obj.style.position = 'relative';
				} else {
					body.className = '';
				}
			}
</script>

控制滚动多少像素后浮空到顶部