Usage

Use the affix plugin via data attributes or manually with your own JavaScript. In both situations, you must provide CSS for the positioning and width of your affixed content.

Positioning via CSS

The affix plugin toggles between three classes, each representing a particular state: .affix, .affix-top, and .affix-bottom. You must provide the styles for these classes yourself (independent of this plugin) to handle the actual positions.

Here's how the affix plugin works:

1. To start, the plugin adds .affix-top to indicate the element is in its top-most position. At this point no CSS positioning is required.
2. Scrolling past the element you want affixed should trigger the actual affixing. This is where .affix replaces .affix-top and sets position: fixed; (provided by Bootstrap's code CSS).
3. If a bottom offset is defined, scrolling past that should replace .affix with .affix-bottom. Since offsets are optional, setting one requires you to set the appropriate CSS. In this case, add position: absolute; when necessary. The plugin uses the data attribute or JavaScript option to determine where to position the element from there.

Follow the above steps to set your CSS for either of the usage options below.

Via data attributes

To easily add affix behavior to any element, just add data-spy="affix" to the element you want to spy on. Use offsets to define when to toggle the pinning of an element.

<div data-spy="affix" data-offset-top="60" data-offset-bottom="200">
  ...
</div>

Via JavaScript

Call the affix plugin via JavaScript:

$('#my-affix').affix({
    offset: {
      top: 100
    , bottom: function () {
        return (this.bottom = $('.footer').outerHeight(true))
      }
    }
  })

Options

Options can be passed via data attributes or JavaScript. For data attributes, append the option name to data-, as in data-offset-top="200".

Events

Bootstrap's affix class exposes a few events for hooking into affix functionality.