bootstrap源码分析之scrollspy（滚动侦听）_html/css_WEB-ITnose
源码文件：
Scrollspy.js
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="ibe">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>
源码分析：
1、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
2、如果滚动区域是body，会将滚动区域元素标记为window（构造函数中判断）
this.$scrollElement = $(element).is(document.body) ? $(window) : $(element)
this.$scrollElement[0].scrollHeight || Math.max(this.$body[0].scrollHeight, document.documentElement.scrollHeight)
4.1、默认用offset来获取定位值，如果滚动区域不是window则用position来获取
if (!$.isWindow(this.$scrollElement[0])) { offsetMethod = 'position' offsetBase = this.$scrollElement.scrollTop() //获取基础高度，如果滚动区域内有不参与滚动计算的内容 }
this.$body .find(this.selector) .map(function () { var $el = $(this) var href = $el.data('target') || $el.attr('href') var $href = /^#./.test(href) && $(href) //获取滚动区域内的hashkey对应的元素 return ($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]) })5.1、获取滚动容器已滚动距离：
var scrollTop = this.$scrollElement.scrollTop() + this.options.offset
//最大可以滚动高度=滚动设置距离（offset）+ 滚动容器内容高度 - 滚动容器设置的高度var maxScroll = this.options.offset + scrollHeight - this.$scrollElement.height()
for (i = offsets.length; i--;) {//遍历所有的offset activeTarget != targets[i] //判断当前target是否等于activeTarget && scrollTop >= offsets[i] //滚动高度>i元素的offset && (offsets[i + 1] === undefined || scrollTop < offsets[i + 1]) //i + 1元素不存在，或者i+1元素不大于滚动高度 && this.activate(targets[i]) //设置i为当前活动项 }7、clear：清除所有高亮菜单
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