bootstrap源码之滚动监听组件scrollspy.js详解

其实滚动监听使用的情况还是很多的，比如导航居于右侧，当主题内容滚动某一块的时候，右侧导航对应的要高亮。

实现功能

1、当滚动区域内设置的hashkey距离顶点到有效位置时，就关联设置其导航上的指定项
2、导航必须是 .nav > li > a 结构，并且a上href或data-target要绑定hashkey
3、菜单上必须有.nav样式
4、滚动区域的data-target与导航父级Id（一定是父级）要一致。

<div id="selector" class="navbar navbar-default">
<ul class="nav navbar-nav">
<li><a href="#one">one</a> </li>
<li><a href="#two">two</a> </li>
<li><a href="#three">three</a> </li>
</ul>
</div>
<div data-spy="scroll" data-target="#selector" style="height:100px; overflow:hidden;overflow-y: auto;" >
<h4 id="one" >ibe</h4><p>One的具体内容<br/>One的具体内容<br/>One的具体内容<br/>One的具体内容<br/>One的具体内容<br/>One的具体内容<br/></p>
<h4 id="two" >two</h4><p>One的具体内容<br/>One的具体内容<br/>One的具体内容<br/>One的具体内容<br/>One的具体内容<br/>One的具体内容<br/></p>
<h4 id="three" >three</h4><p>One的具体内容<br/>One的具体内容<br/>One的具体内容<br/>One的具体内容<br/>One的具体内容<br/>One的具体内容<br/></p>
</div>

下面来看一下实现的具体代码，原理：当滚动容器内的hashkey位置距离容器顶部只有 offset设置的值，就会设置导航中对应的href高亮。

ScrollSpy构造函数

首先新建一个构造函数，如下：

function ScrollSpy(element, options) {
this.$body          = $(document.body)
this.$scrollElement = $(element).is(document.body) ? $(window) : $(element)
this.options        = $.extend({}, ScrollSpy.DEFAULTS, options)
this.selector       = (this.options.target || '')   ' .nav li > a'
this.offsets        = []
this.targets        = []
this.activeTarget   = null
this.scrollHeight   = 0
this.$scrollElement.on('scroll.bs.scrollspy', $.proxy(this.process, this))
this.refresh()
this.process()
}

该构造函数主要干了啥：

1.基本设置，主要是设置当前滚动元素是设置的body还是具体的某一块元素；其次是导航的结构要是.nav li > a的结构，也就是你的菜单中也要有.nav这个class。

2.监听元素滚动的时候，执行process方法。

3.同时初始化的时候也执行了refresh与process方法。

下面讲解一下这几个方法。

getScrolHeight方法

获取滚动容器的内容高度（包含被隐藏部分）

this.$scrollElement[0].scrollHeight || Math.max(this.$body[0].scrollHeight, document.documentElement.scrollHeight)

refresh方法

刷新并存储滚动容器内各hashkey的值

ScrollSpy.prototype.refresh = function () {
var that          = this
var offsetMethod  = 'offset'
var offsetBase    = 0
this.offsets      = []
this.targets      = []
this.scrollHeight = this.getScrollHeight()
if (!$.isWindow(this.$scrollElement[0])) {
offsetMethod = 'position'
offsetBase   = this.$scrollElement.scrollTop()
}
this.$body
.find(this.selector)
.map(function () {
var $el   = $(this)
var href  = $el.data('target') || $el.attr('href')
var $href = /^#./.test(href) && $(href)
return ($href
&& $href.length
&& $href.is(':visible')
&& [[$href[offsetMethod]().top   offsetBase, href]]) || null
})
.sort(function (a, b) { return a[0] - b[0] })
.each(function () {
that.offsets.push(this[0])
that.targets.push(this[1])
})
}

它主要实现了什么呢？

1.默认用offset来获取定位值，如果滚动区域不是window则用position来获取

if (!$.isWindow(this.$scrollElement[0])) {
offsetMethod = 'position'
offsetBase   = this.$scrollElement.scrollTop()
}

2.根据导航上的hashkey来遍历获取滚动区域内的hashkey对应的offset值：

this.$body
.find(this.selector)
.map(function () {
var $el   = $(this)
var href  = $el.data('target') || $el.attr('href')
var $href = /^#./.test(href) && $(href)
return ($href
&& $href.length
&& $href.is(':visible')
&& [[$href[offsetMethod]().top   offsetBase, href]]) || null
})
.sort(function (a, b) { return a[0] - b[0] })
.each(function () {
that.offsets.push(this[0])
that.targets.push(this[1])
})

process方法

滚动条事件触发函数，用于计算当前需要高亮那个导航菜单

ScrollSpy.prototype.process = function () {
var scrollTop    = this.$scrollElement.scrollTop()   this.options.offset
var scrollHeight = this.getScrollHeight()
var maxScroll    = this.options.offset   scrollHeight - this.$scrollElement.height()
var offsets      = this.offsets
var targets      = this.targets
var activeTarget = this.activeTarget
var i
if (this.scrollHeight != scrollHeight) {
this.refresh()
}
if (scrollTop >= maxScroll) {
return activeTarget != (i = targets[targets.length - 1]) && this.activate(i)
}
if (activeTarget && scrollTop < offsets[0]) {
this.activeTarget = null
return this.clear()
}
for (i = offsets.length; i--;) {
activeTarget != targets[i]
&& scrollTop >= offsets[i]
&& (offsets[i   1] === undefined || scrollTop < offsets[i   1])
&& this.activate(targets[i])
}
}

主要作用：

1.获取滚动容器已滚动距离：

var scrollTop    = this.$scrollElement.scrollTop()   this.options.offset

2.滚动容器可以滚动的最大高度:

var maxScroll    = this.options.offset   scrollHeight - this.$scrollElement.height()

3.设置滚动元素逻辑，给当前匹配元素添加高亮：

for (i = offsets.length; i--;) {
activeTarget != targets[i]
&& scrollTop >= offsets[i]
&& (offsets[i   1] === undefined || scrollTop < offsets[i   1])
&& this.activate(targets[i])
}

active方法

设置指定的导航菜单高亮

ScrollSpy.prototype.activate = function (target) {
this.activeTarget = target
this.clear()
var selector = this.selector
'[data-target="'   target   '"],'
this.selector   '[href="'   target   '"]'
var active = $(selector)
.parents('li')
.addClass('active')
if (active.parent('.dropdown-menu').length) {
active = active
.closest('li.dropdown')
.addClass('active')
}
active.trigger('activate.bs.scrollspy')
}

clear方法

清除所有高亮菜单

ScrollSpy.prototype.clear = function () {
$(this.selector)
.parentsUntil(this.options.target, '.active')
.removeClass('active')
}

源码

 function ($) {
'use strict';
// SCROLLSPY CLASS DEFINITION
// ==========================
function ScrollSpy(element, options) {
this.$body          = $(document.body)
this.$scrollElement = $(element).is(document.body) ? $(window) : $(element)
this.options        = $.extend({}, ScrollSpy.DEFAULTS, options)
this.selector       = (this.options.target || '')   ' .nav li > a'
this.offsets        = []
this.targets        = []
this.activeTarget   = null
this.scrollHeight   = 0
this.$scrollElement.on('scroll.bs.scrollspy', $.proxy(this.process, this))
this.refresh()
this.process()
}
ScrollSpy.VERSION  = '3.3.7'
ScrollSpy.DEFAULTS = {
offset: 10
}
ScrollSpy.prototype.getScrollHeight = function () {
return this.$scrollElement[0].scrollHeight || Math.max(this.$body[0].scrollHeight, document.documentElement.scrollHeight)
}
ScrollSpy.prototype.refresh = function () {
var that          = this
var offsetMethod  = 'offset'
var offsetBase    = 0
this.offsets      = []
this.targets      = []
this.scrollHeight = this.getScrollHeight()
if (!$.isWindow(this.$scrollElement[0])) {
offsetMethod = 'position'
offsetBase   = this.$scrollElement.scrollTop()
}
this.$body
.find(this.selector)
.map(function () {
var $el   = $(this)
var href  = $el.data('target') || $el.attr('href')
var $href = /^#./.test(href) && $(href)
return ($href
&& $href.length
&& $href.is(':visible')
&& [[$href[offsetMethod]().top   offsetBase, href]]) || null
})
.sort(function (a, b) { return a[0] - b[0] })
.each(function () {
that.offsets.push(this[0])
that.targets.push(this[1])
})
}
ScrollSpy.prototype.process = function () {
var scrollTop    = this.$scrollElement.scrollTop()   this.options.offset
var scrollHeight = this.getScrollHeight()
var maxScroll    = this.options.offset   scrollHeight - this.$scrollElement.height()
var offsets      = this.offsets
var targets      = this.targets
var activeTarget = this.activeTarget
var i
if (this.scrollHeight != scrollHeight) {
this.refresh()
}
if (scrollTop >= maxScroll) {
return activeTarget != (i = targets[targets.length - 1]) && this.activate(i)
}
if (activeTarget && scrollTop < offsets[0]) {
this.activeTarget = null
return this.clear()
}
for (i = offsets.length; i--;) {
activeTarget != targets[i]
&& scrollTop >= offsets[i]
&& (offsets[i   1] === undefined || scrollTop < offsets[i   1])
&& this.activate(targets[i])
}
}
ScrollSpy.prototype.activate = function (target) {
this.activeTarget = target
this.clear()
var selector = this.selector
'[data-target="'   target   '"],'
this.selector   '[href="'   target   '"]'
var active = $(selector)
.parents('li')
.addClass('active')
if (active.parent('.dropdown-menu').length) {
active = active
.closest('li.dropdown')
.addClass('active')
}
active.trigger('activate.bs.scrollspy')
}
ScrollSpy.prototype.clear = function () {
$(this.selector)
.parentsUntil(this.options.target, '.active')
.removeClass('active')
}
// SCROLLSPY PLUGIN DEFINITION
// ===========================
function Plugin(option) {
return this.each(function () {
var $this   = $(this)
var data    = $this.data('bs.scrollspy')
var options = typeof option == 'object' && option
if (!data) $this.data('bs.scrollspy', (data = new ScrollSpy(this, options)))
if (typeof option == 'string') data[option]()
})
}
var old = $.fn.scrollspy
$.fn.scrollspy             = Plugin
$.fn.scrollspy.Constructor = ScrollSpy
// SCROLLSPY NO CONFLICT
// =====================

$.fn.scrollspy.noConflict = function () {
$.fn.scrollspy = old
return this
}
// SCROLLSPY DATA-API
// ==================

$(window).on('load.bs.scrollspy.data-api', function () {
$('[data-spy="scroll"]').each(function () {
var $spy = $(this)
Plugin.call($spy, $spy.data())
})
})
}(jQuery);

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