Bootstrap/docs/_includes/js/affix.html

<div class="bs-docs-section">
  <h1 id="affix" class="page-header">Affix <small>affix.js</small></h1>

  <h2 id="affix-examples">Example</h2>
  <p>The affix plugin toggles <code>position: fixed;</code> on and off, emulating the effect found with <a href="https://developer.mozilla.org/en-US/docs/Web/CSS/position#Sticky_positioning"><code>position: sticky;</code></a>. The subnavigation on the right is a live demo of the affix plugin.</p>

  <hr class="bs-docs-separator">

  <h2 id="affix-usage">Usage</h2>
  <p>Use the affix plugin via data attributes or manually with your own JavaScript. <strong class="text-danger">In both situations, you must provide CSS for the positioning and width of your affixed content.</strong></p>
  <p>Note: Do not use the affix plugin on an element contained in a relatively positioned element, such as a pulled or pushed column, due to a <a href="https://github.com/twbs/bootstrap/issues/12126">Safari rendering bug</a>.</p>

  <h3>Positioning via CSS</h3>
  <p>The affix plugin toggles between three classes, each representing a particular state: <code>.affix</code>, <code>.affix-top</code>, and <code>.affix-bottom</code>. You must provide the styles, with the exception of <code>position: fixed;</code> on <code>.affix</code>, for these classes yourself (independent of this plugin) to handle the actual positions.</p>
  <p>Here's how the affix plugin works:</p>
  <ol>
    <li>To start, the plugin adds <code>.affix-top</code> to indicate the element is in its top-most position. At this point no CSS positioning is required.</li>
    <li>Scrolling past the element you want affixed should trigger the actual affixing. This is where <code>.affix</code> replaces <code>.affix-top</code> and sets <code>position: fixed;</code> (provided by Bootstrap's CSS).</li>
    <li>If a bottom offset is defined, scrolling past it should replace <code>.affix</code> with <code>.affix-bottom</code>. Since offsets are optional, setting one requires you to set the appropriate CSS. In this case, add <code>position: absolute;</code> when necessary. The plugin uses the data attribute or JavaScript option to determine where to position the element from there.</li>
  </ol>
  <p>Follow the above steps to set your CSS for either of the usage options below.</p>

  <h3>Via data attributes</h3>
  <p>To easily add affix behavior to any element, just add <code>data-spy="affix"</code> to the element you want to spy on. Use offsets to define when to toggle the pinning of an element.</p>

{% highlight html %}
<div data-spy="affix" data-offset-top="60" data-offset-bottom="200">
  ...
</div>
{% endhighlight %}

  <h3>Via JavaScript</h3>
  <p>Call the affix plugin via JavaScript:</p>
{% highlight js %}
$('#myAffix').affix({
  offset: {
    top: 100,
    bottom: function () {
      return (this.bottom = $('.footer').outerHeight(true))
    }
  }
})
{% endhighlight %}


  <h3 id="affix-options">Options</h3>
  <p>Options can be passed via data attributes or JavaScript. For data attributes, append the option name to <code>data-</code>, as in <code>data-offset-top="200"</code>.</p>

  <div class="table-responsive">
    <table class="table table-bordered table-striped js-options-table">
      <thead>
       <tr>
         <th>Name</th>
         <th>type</th>
         <th>default</th>
         <th>description</th>
       </tr>
      </thead>
      <tbody>
       <tr>
         <td>offset</td>
         <td>number | function | object</td>
         <td>10</td>
         <td>Pixels to offset from screen when calculating position of scroll. If a single number is provided, the offset will be applied in both top and bottom directions. To provide a unique, bottom and top offset just provide an object <code>offset: { top: 10 }</code> or <code>offset: { top: 10, bottom: 5 }</code>. Use a function when you need to dynamically calculate an offset.</td>
       </tr>
       <tr>
         <td>target</td>
         <td>selector | node | jQuery element</td>
         <td>the <code>window</code> object</td>
         <td>Specifies the target element of the affix.</td>
       </tr>

      </tbody>
    </table>
  </div><!-- /.table-responsive -->


  <h3 id="affix-events">Events</h3>
  <p>Bootstrap's affix plugin exposes a few events for hooking into affix functionality.</p>
  <div class="table-responsive">
    <table class="table table-bordered table-striped bs-events-table">
      <thead>
        <tr>
          <th>Event Type</th>
          <th>Description</th>
        </tr>
      </thead>
      <tbody>
        <tr>
          <td>affix.bs.affix</td>
          <td>This event fires immediately before the element has been affixed.</td>
        </tr>
        <tr>
          <td>affixed.bs.affix</td>
          <td>This event is fired after the element has been affixed.</td>
        </tr>
        <tr>
          <td>affix-top.bs.affix</td>
          <td>This event fires immediately before the element has been affixed-top.</td>
        </tr>
        <tr>
          <td>affixed-top.bs.affix</td>
          <td>This event is fired after the element has been affixed-top.</td>
        </tr>
       <tr>
        <td>affix-bottom.bs.affix</td>
          <td>This event fires immediately before the element has been affixed-bottom.</td>
        </tr>
        <tr>
          <td>affixed-bottom.bs.affix</td>
          <td>This event is fired after the element has been affixed-bottom.</td>
        </tr>
      </tbody>
    </table>
  </div><!-- /.table-responsive -->
</div>