https://www.archives.gov/sites/all/themes/nara/assets/javascripts/bootstrap/affix.js?tm7hkg

1/* ========================================================================
2 * Bootstrap: affix.js v3.2.0
3 * http://getbootstrap.com/javascript/#affix
4 * ========================================================================
5 * Copyright 2011-2014 Twitter, Inc.
6 * Licensed under MIT (https://github.com/twbs/bootstrap/blob/master/LICENSE)
7 * ======================================================================== */
8
9
10+function ($) {
11  'use strict';
12
13  // AFFIX CLASS DEFINITION
14  // ======================
15
16  var Affix = function (element, options) {
17    this.options = $.extend({}, Affix.DEFAULTS, options)
18
19    this.$target = $(this.options.target)
20      .on('scroll.bs.affix.data-api', $.proxy(this.checkPosition, this))
21      .on('click.bs.affix.data-api',  $.proxy(this.checkPositionWithEventLoop, this))
22
23    this.$element     = $(element)
24    this.affixed      =
25    this.unpin        =
26    this.pinnedOffset = null
27
28    this.checkPosition()
29  }
30
31  Affix.VERSION  = '3.2.0'
32
33  Affix.RESET    = 'affix affix-top affix-bottom'
34
35  Affix.DEFAULTS = {
36    offset: 0,
37    target: window
38  }
39
40  Affix.prototype.getPinnedOffset = function () {
41    if (this.pinnedOffset) return this.pinnedOffset
42    this.$element.removeClass(Affix.RESET).addClass('affix')
43    var scrollTop = this.$target.scrollTop()
44    var position  = this.$element.offset()
45    return (this.pinnedOffset = position.top - scrollTop)
46  }
47
48  Affix.prototype.checkPositionWithEventLoop = function () {
49    setTimeout($.proxy(this.checkPosition, this), 1)
50  }
51
52  Affix.prototype.checkPosition = function () {
53    if (!this.$element.is(':visible')) return
54
55    var scrollHeight = $(document).height()
56    var scrollTop    = this.$target.scrollTop()
57    var position     = this.$element.offset()
58    var offset       = this.options.offset
59    var offsetTop    = offset.top
60    var offsetBottom = offset.bottom
61
62    if (typeof offset != 'object')         offsetBottom = offsetTop = offset
63    if (typeof offsetTop == 'function')    offsetTop    = offset.top(this.$element)
64    if (typeof offsetBottom == 'function') offsetBottom = offset.bottom(this.$element)
65
66    var affix = this.unpin   != null && (scrollTop + this.unpin <= position.top) ? false :
67                offsetBottom != null && (position.top + this.$element.height() >= scrollHeight - offsetBottom) ? 'bottom' :
68                offsetTop    != null && (scrollTop <= offsetTop) ? 'top' : false
69
70    if (this.affixed === affix) return
71    if (this.unpin != null) this.$element.css('top', '')
72
73    var affixType = 'affix' + (affix ? '-' + affix : '')
74    var e         = $.Event(affixType + '.bs.affix')
75
76    this.$element.trigger(e)
77
78    if (e.isDefaultPrevented()) return
79
80    this.affixed = affix
81    this.unpin = affix == 'bottom' ? this.getPinnedOffset() : null
82
83    this.$element
84      .removeClass(Affix.RESET)
85      .addClass(affixType)
86      .trigger($.Event(affixType.replace('affix', 'affixed')))
87
88    if (affix == 'bottom') {
89      this.$element.offset({
90        top: scrollHeight - this.$element.height() - offsetBottom
91      })
92    }
93  }
94
95
96  // AFFIX PLUGIN DEFINITION
97  // =======================
98
99  function Plugin(option) {
100    return this.each(function () {
101      var $this   = $(this)
102      var data    = $this.data('bs.affix')
103      var options = typeof option == 'object' && option
104
105      if (!data) $this.data('bs.affix', (data = new Affix(this, options)))
106      if (typeof option == 'string') data[option]()
107    })
108  }
109
110  var old = $.fn.affix
111
112  $.fn.affix             = Plugin
113  $.fn.affix.Constructor = Affix
114
115
116  // AFFIX NO CONFLICT
117  // =================
118
119  $.fn.affix.noConflict = function () {
120    $.fn.affix = old
121    return this
122  }
123
124
125  // AFFIX DATA-API
126  // ==============
127
128  $(window).on('load', function () {
129    $('[data-spy="affix"]').each(function () {
130      var $spy = $(this)
131      var data = $spy.data()
132
133      data.offset = data.offset || {}
134
135      if (data.offsetBottom) data.offset.bottom = data.offsetBottom
136      if (data.offsetTop)    data.offset.top    = data.offsetTop
137
138      Plugin.call($spy, data)
139    })
140  })
141
142}(jQuery);