bootstrap源码分析之scrollspy（滚动侦听）

<span style="color: #800000"><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></span>

<span style="color: #0000ff">this</span>.$scrollElement = $(element).is(document.body) ? $(window) : $(element)

<span style="color: #0000ff">this</span>.$scrollElement[0].scrollHeight || Math.max(<span style="color: #0000ff">this</span>.$body[0].scrollHeight, document.documentElement.scrollHeight)

<span style="color: #0000ff">if</span> (!$.isWindow(<span style="color: #0000ff">this</span>.$scrollElement[0<span style="color: #000000">])) {
      offsetMethod </span>= 'position'<span style="color: #000000">
      offsetBase   </span>= <span style="color: #0000ff">this</span>.$scrollElement.scrollTop() <span style="color: #008000">//</span><span style="color: #008000">获取基础高度，如果滚动区域内有不参与滚动计算的内容</span>
   }

<span style="color: #0000ff">this</span><span style="color: #000000">.$body
     .find(</span><span style="color: #0000ff">this</span><span style="color: #000000">.selector)
      .map(</span><span style="color: #0000ff">function</span><span style="color: #000000"> () {
        </span><span style="color: #0000ff">var</span> $el   = $(<span style="color: #0000ff">this</span><span style="color: #000000">)
        </span><span style="color: #0000ff">var</span> href  = $el.data('target') || $el.attr('href'<span style="color: #000000">)
        </span><span style="color: #0000ff">var</span> $href = /^#./.test(href) && $(href) <span style="color: #008000">//</span><span style="color: #008000">获取滚动区域内的hashkey对应的元素</span>

        <span style="color: #0000ff">return</span><span style="color: #000000"> ($href
          </span>&&<span style="color: #000000"> $href.length
          </span>&& $href.is(':visible'<span style="color: #000000">)
          </span>&& [[$href[offsetMethod]().top + offsetBase, href]]) || <span style="color: #0000ff">null</span><span style="color: #000000">
      })
      .sort(</span><span style="color: #0000ff">function</span> (a, b) { <span style="color: #0000ff">return</span> a[0] - b[0<span style="color: #000000">] })
      .each(</span><span style="color: #0000ff">function</span><span style="color: #000000"> () {
        that.offsets.push(</span><span style="color: #0000ff">this</span>[0<span style="color: #000000">])
        that.targets.push(</span><span style="color: #0000ff">this</span>[1<span style="color: #000000">])
      })</span>

<span style="color: #0000ff">var</span> scrollTop    = <span style="color: #0000ff">this</span>.$scrollElement.scrollTop() + <span style="color: #0000ff">this</span>.options.offset

<span style="color: #008000">//</span><span style="color: #008000">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</span>
<span style="color: #0000ff">var</span> maxScroll    = <span style="color: #0000ff">this</span>.options.offset + scrollHeight - <span style="color: #0000ff">this</span>.$scrollElement.height()

<span style="color: #0000ff">for</span> (i = offsets.length; i--;) {<span style="color: #008000">//</span><span style="color: #008000">遍历所有的offset</span>
     activeTarget != targets[i] <span style="color: #008000">//</span><span style="color: #008000">判断当前target是否等于activeTarget</span>
        && scrollTop >= offsets[i] <span style="color: #008000">//</span><span style="color: #008000">滚动高度>i元素的offset</span>
        && (offsets[i + 1] === undefined || scrollTop < offsets[i + 1]) <span style="color: #008000">//</span><span style="color: #008000">i + 1元素不存在，或者i+1元素不大于滚动高度</span>
        && <span style="color: #0000ff">this</span>.activate(targets[i]) <span style="color: #008000">//</span><span style="color: #008000">设置i为当前活动项</span>
    }