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<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta http-equiv="X-UA-Compatible" content="ie=edge">
  <title>吸顶容器</title>
  <style>
    body {
      margin: 0px !important;
      padding: 0;
      box-sizing: border-box;
    }
	.cont{
	  margin: 0 10px;
	}
    .road-tab-fixed {
      position: fixed;
      top: 0;
	  left: 10px;
      right: 10px;
    }
	.wrapper{
	  height: 50px;
	  width: 100%;
	  
	}
    .top {
      background: #c4f8b4;
      height: 50px;
    }

    .list {
      background: #ccc;
      width: 100%;
    }

    .list li {
      height: 50px;
      border-bottom: 2px solid #f00;
    }

    .banner {
      width: 100%;
      background: #c19aff;
      height: 150px;
    }
  </style>
</head>

<body>
  <div class="cont">
    <div class="banner">这是广告图</div>
    <div class="wrapper"><div class="top" id="road-tab">菜单</div></div>
    <div class="list">
      <ul>
        <li>0</li>
        <li>1</li>
        <li>2</li>
        <li>3</li>
        <li>4</li>
        <li>5</li>
        <li>6</li>
        <li>7</li>
        <li>8</li>
        <li>9</li>
        <li>0</li>
        <li>1</li>
        <li>2</li>
        <li>3</li>
        <li>4</li>
        <li>5</li>
        <li>6</li>
        <li>7</li>
        <li>8</li>
        <li>9</li>
      </ul>
    </div>
  </div>
  <script src="https://cdn.bootcss.com/jquery/1.10.2/jquery.min.js"></script>
  <script>
    var fixedDom = $("#road-tab"),
      tabclass = "road-tab-fixed";
    var beforeElementScrollTop = 0;
    var beforeOffsetTop = fixedDom[0].offsetTop;
    //scroll节流
    var throttle = function(fn, delay, mustRunDelay){
      var timer = null;
      var t_start;
      return function(){
        var context = this, args = arguments, t_curr = +new Date();
        clearTimeout(timer);
        if(!t_start){
          t_start = t_curr;
        }
        if(t_curr - t_start >= mustRunDelay){
          fn.apply(context, args);
          t_start = t_curr;
        }
        else {
          timer = setTimeout(function(){
            fn.apply(context, args);
          }, delay);
        }
      };
    };
    var winScroll = function(e) {
      var elementScrollTop = getScrollTop()
      //console.log('elementScrollTop--------------', elementScrollTop);
      if (beforeElementScrollTop - elementScrollTop <= 0) {
        if (beforeOffsetTop - elementScrollTop < 0) {
          fixedDom.addClass("road-tab-fixed")
        }
      } else {
        if (beforeOffsetTop - elementScrollTop >= 0) {
          fixedDom.removeClass("road-tab-fixed")
        }
      }
      beforeElementScrollTop = getScrollTop()
    };
    var getScrollTop = function(){
      return document.documentElement.scrollTop || window.pageYOffset || document.body.scrollTop
    }
    
    $(window).off("scroll").on("scroll",throttle(winScroll, 10, 100));
  </script>
</body>
</html>