二级菜单粘到标题

Question

我在页面顶部有一个固定的标题，在向下滚动并显示一个滑块后，我有一个辅助锚点菜单。如何让这个锚点菜单粘到标题上。

Answer 1

我非常确定这是你正在寻找的东西！

https://codepen.io/will0220/pen/QqreKY

基本上，您需要从屏幕顶部检查中间内容导航栏的位置，这是通过检查元素的顶部偏移减去窗口的滚动来完成的。如果您向上或向下滚动，请进行操作 - 因此，如果您向下滚动，并且中间页面导航小于屏幕顶部固定标题的高度，请将其克隆并添加它的固定版本。克隆是要走的路，所以内容长度不会改变。然后，当我们向相反方向滚动时，我们可以使用与之前相同的计算来检查原始页内导航（仍然存在）的位置。

这将处理固定导航栏中的切换：

var thisScroll = 0, lastScroll = 0;
$(window).scroll(function(){
  thisScroll = $(window).scrollTop();
  if($('nav').offset().top - thisScroll <= 50 && !$('#stuckNav').length && thisScroll > lastScroll){
    var newNav = $('nav').clone();
    newNav.attr('id', 'stuckNav');
    $('#wrapper').append(newNav);
  }
  else if($('nav').offset().top - $(window).scrollTop() > 50 && thisScroll < lastScroll){
    $('#stuckNav').remove();
  }
  lastScroll = thisScroll;
});

CSS需要这样的东西：

 #stuckNav{
  position: fixed;
  top: 50px;
  z-index: 2;
}
nav{
  position: relative;
  width: 100%;
  background: #FFF;
  text-align: center;
  padding: 10px 0;
}

Answer 2

仅使用javascript：https://codepen.io/claytron5000/pen/OxZKxB?editors=1010

var secondary = document.querySelector(".secondary");

var fromTop = secondary.offsetTop;

document.onscroll = function() {
  if (!secondary.classList.contains("stuck") && window.pageYOffset >= fromTop) {
    secondary.classList.add("stuck");
  }
  else if (secondary.classList.contains("stuck") && window.pageYOffset < fromTop){
    secondary.classList.remove("stuck");
  }
};

.container p {
  max-width: 768px;
  margin: auto;
}
.header, .secondary {
  background: beige;
  position: relative;
}
ul li {
  display: inline-block;
  background: lightgrey;
}
.stuck {
  position: fixed;
  top:0;
  width: 100%;
}

<div id="container">
  <div class="header">
    <ul>
      <li>here's</li>
      <li>some</li>
      <li>items</li>
    </ul>
  </div>
  <p>Some content that will scroll away.</p>
  <div class="secondary">
    <ul>
      <li>here's</li>
      <li>different</li>
      <li>items</li>
    </ul>
  </div>
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    Why do we use it?
    It is a long established fact that a reader will be distracted by the readable content of a page when looking at its layout. The point of using Lorem Ipsum is that it has a more-or-less normal distribution of letters, as opposed to using 'Content here, content here', making it look like readable English. Many desktop publishing packages and web page editors now use Lorem Ipsum as their default model text, and a search for 'lorem ipsum' will uncover many web sites still in their infancy. Various versions have evolved over the years, sometimes by accident, sometimes on purpose (injected humour and the like).
    Why do we use it?
    It is a long established fact that a reader will be distracted by the readable content of a page when looking at its layout. The point of using Lorem Ipsum is that it has a more-or-less normal distribution of letters, as opposed to using 'Content here, content here', making it look like readable English. Many desktop publishing packages and web page editors now use Lorem Ipsum as their default model text, and a search for 'lorem ipsum' will uncover many web sites still in their infancy. Various versions have evolved over the years, sometimes by accident, sometimes on purpose (injected humour and the like).
    Why do we use it?
    It is a long established fact that a reader will be distracted by the readable content of a page when looking at its layout. The point of using Lorem Ipsum is that it has a more-or-less normal distribution of letters, as opposed to using 'Content here, content here', making it look like readable English. Many desktop publishing packages and web page editors now use Lorem Ipsum as their default model text, and a search for 'lorem ipsum' will uncover many web sites still in their infancy. Various versions have evolved over the years, sometimes by accident, sometimes on purpose (injected humour and the like).
    Why do we use it?
    It is a long established fact that a reader will be distracted by the readable content of a page when looking at its layout. The point of using Lorem Ipsum is that it has a more-or-less normal distribution of letters, as opposed to using 'Content here, content here', making it look like readable English. Many desktop publishing packages and web page editors now use Lorem Ipsum as their default model text, and a search for 'lorem ipsum' will uncover many web sites still in their infancy. Various versions have evolved over the years, sometimes by accident, sometimes on purpose (injected humour and the like).
    Why do we use it?
    It is a long established fact that a reader will be distracted by the readable content of a page when looking at its layout. The point of using Lorem Ipsum is that it has a more-or-less normal distribution of letters, as opposed to using 'Content here, content here', making it look like readable English. Many desktop publishing packages and web page editors now use Lorem Ipsum as their default model text, and a search for 'lorem ipsum' will uncover many web sites still in their infancy. Various versions have evolved over the years, sometimes by accident, sometimes on purpose (injected humour and the like).


    Where does it come from?
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</div>