含有滚动条元素的getBoundingClientRect等属性的值
问题1：首先我们给出iScroll的一个官方的demo,你可以把这个demo拷贝到本地然后运行，或者去github下载
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0, user-scalable=0, minimum-scale=1.0, maximum-scale=1.0">
<title>iScroll demo: scrollbars</title>
<script type="text/javascript" src="../../build/iscroll.js"></script>
<script type="text/javascript">
var myScroll;
function loaded () {
myScroll = new IScroll('#wrapper', {
scrollbars: true,
mouseWheel: true,
interactiveScrollbars: true,
shrinkScrollbars: 'scale',
fadeScrollbars: false,
momentum:true,
shrinkScrollbars:'clip',
keyBindings:true
});
}
document.addEventListener('touchmove', function (e) { e.preventDefault(); }, false);
</script>
<style type="text/css">
* {
-webkit-box-sizing: border-box;
-moz-box-sizing: border-box;
box-sizing: border-box;
}
html {
-ms-touch-action: none;
}
body,ul,li {
padding: 0;
margin: 0;
border: 0;
}
body {
font-size: 12px;
font-family: ubuntu, helvetica, arial;
overflow: hidden; /* this is important to prevent the whole page to bounce */
}
.iScrollIndicator{
background-color:red!important;
}
.iScrollVerticalScrollbar{
background-color:blue!important;
}
#header {
position: absolute;
z-index: 2;
top: 0;
left: 0;
width: 100%;
height: 45px;
line-height: 45px;
background: #CD235C;
padding: 0;
color: #eee;
font-size: 20px;
text-align: center;
font-weight: bold;
}
#footer {
position: absolute;
z-index: 2;
bottom: 0;
left: 0;
width: 100%;
height: 48px;
background: #444;
padding: 0;
border-top: 1px solid #444;
}
#wrapper {
position: absolute;
z-index: 1;
top: 145px;
border:1px solid red;
bottom: 48px;
width: 500px;
background: #ccc;
overflow: hidden;
left:400px;
height:600px;
}
#scroller {
position: absolute;
z-index: 1;
-webkit-tap-highlight-color: rgba(0,0,0,0);
width: 100%;
-webkit-transform: translateZ(0);
-moz-transform: translateZ(0);
-ms-transform: translateZ(0);
-o-transform: translateZ(0);
transform: translateZ(0);
-webkit-touch-callout: none;
-webkit-user-select: none;
-moz-user-select: none;
-ms-user-select: none;
user-select: none;
-webkit-text-size-adjust: none;
-moz-text-size-adjust: none;
-ms-text-size-adjust: none;
-o-text-size-adjust: none;
text-size-adjust: none;
}
#scroller ul {
list-style: none;
padding: 0;
margin: 0;
width: 100%;
text-align: left;
}
#scroller li {
padding: 0 10px;
height: 40px;
line-height: 40px;
border-bottom: 1px solid #ccc;
border-top: 1px solid #fff;
background-color: #fafafa;
font-size: 14px;
}
</style>
</head>
<body onload="loaded()">
<div id="header">iScroll</div>
<div id="wrapper">
<div id="scroller">
<ul>
<li>Pretty row 1</li>
<li>Pretty row 2</li>
<li>Pretty row 3</li>
<li>Pretty row 4</li>
<li>Pretty row 5</li>
<li>Pretty row 6</li>
<li>Pretty row 7</li>
<li>Pretty row 8</li>
<li>Pretty row 9</li>
<li>Pretty row 10</li>
<li>Pretty row 11</li>
<li>Pretty row 12</li>
<li>Pretty row 13</li>
<li>Pretty row 14</li>
<li>Pretty row 15</li>
<li>Pretty row 16</li>
<li>Pretty row 17</li>
<li>Pretty row 18</li>
<li>Pretty row 19</li>
<li>Pretty row 20</li>
<li>Pretty row 21</li>
<li>Pretty row 22</li>
<li>Pretty row 23</li>
<li>Pretty row 24</li>
<li>Pretty row 25</li>
<li>Pretty row 26</li>
<li>Pretty row 27</li>
<li>Pretty row 28</li>
<li>Pretty row 29</li>
<li>Pretty row 30</li>
<li>Pretty row 31</li>
<li>Pretty row 32</li>
<li>Pretty row 33</li>
<li>Pretty row 34</li>
<li>Pretty row 35</li>
<li>Pretty row 36</li>
<li>Pretty row 37</li>
<li>Pretty row 38</li>
<li>Pretty row 39</li>
<li>Pretty row 40</li>
<li>Pretty row 41</li>
<li>Pretty row 42</li>
<li>Pretty row 43</li>
<li>Pretty row 44</li>
<li>Pretty row 45</li>
<li>Pretty row 46</li>
<li>Pretty row 47</li>
<li>Pretty row 48</li>
<li>Pretty row 49</li>
<li>Pretty row 50</li>
</ul>
</div>
</div>
<div id="footer" style="background-color:yellow"></div>
</body>
</html>
问题2：计算getBoundingClientRect的值？
如果你随意滚动一下iScroll，然后运行下面的代码：
document.getElementById('wrapper').getBoundingClientRect()
document.getElementById('scroller').getBoundingClientRect()注意：这时候你就会发现wrapper的值就是到文档顶部距离的高度；而scroller的值=iScroll滚动的距离(向上为负数)+wrapper到文档的距离。其中iScroll滚动的距离可以在控制台中看到。就是下面的scroller元素的transform的translate的值：
<div id="scroller" style="transition-timing-function: cubic-bezier(0.1, 0.57, 0.1, 1); transition-duration: 0ms; transform: translate(0px, -603px) translateZ(0px);"> </div>问题3：iScroll中的offsetTop/offsetLeft如何变化？
首先我们看看iScroll的配置项：
myScroll = new IScroll('#wrapper', {
scrollbars: true,
mouseWheel: true,
interactiveScrollbars: true,
shrinkScrollbars: 'scale',
fadeScrollbars: false,
momentum:true,
shrinkScrollbars:'clip',
useTransform:true,//默认为true
keyBindings:true
});注意：因为iScroll默认使用了transform:translate这种方式，所以其不会修改scroller元素和wrapper元素间距，所以scroller元素的offsetLeft/offsetTop的值都是0。
document.getElementById('scroller').offsetTop
document.getElementById('scroller').offsetTop但是，如果你把上面的useTransform设置为false，你就会发现这时候就是通过修改top/left值来导致滚动的。scroller元素的offsetTop/offsetLeft都会有值。
<div id="scroller" style="transition-timing-function: cubic-bezier(0.1, 0.57, 0.1, 1); transition-duration: 0ms; left: 0px; top: -340px;"></div>总结：如果使用了translate来产生滚动，这时候的offsetTop/offsetLeft等都是不会发生变化的。