Progress，进度条，用于上传、下载等耗时并且需要显示进度的场景，用户可以随时中断该操作。
完整的进度条结构如下：
~~~
<div class="weui-progress">
<div class="weui-progress__bar">
<div class="weui-progress__inner-bar js_progress" style="width: 0%;"></div>
</div>
<a href="javascript:;" class="weui-progress__opr">
<i class="weui-icon-cancel"></i>
</a>
</div>
<br>
<div class="weui-progress">
<div class="weui-progress__bar">
<div class="weui-progress__inner-bar js_progress" style="width: 50%;"></div>
</div>
<a href="javascript:;" class="weui-progress__opr">
<i class="weui-icon-cancel"></i>
</a>
</div>
<br>
<div class="weui-progress">
<div class="weui-progress__bar">
<div class="weui-progress__inner-bar js_progress" style="width: 80%;"></div>
</div>
<a href="javascript:;" class="weui-progress__opr">
<i class="weui-icon-cancel"></i>
</a>
</div>
<div class="weui-btn-area">
<a href="javascript:;" class="weui-btn weui-btn_primary" id="btnStartProgress">上传</a>
</div>
~~~
`div.weui-progress__inner-bar` 的默认宽度为 0， 改变改元素的宽度（百分比），即可显示不同的进度。
点击 `a.weui-progress__opr` 元素，可以中断/取消正在进行的操作；如果不需要该操作，则可以省略掉该结构，进度条长度自动适应。
下面模拟改变进度条的值：
~~~
$(function(){
var progress = 0;
var $progress = $('.weui-progress__inner-bar');
function uploading(){
$progress.width(++progress % 100 + '%');
setTimeout(uploading, 20);
}
setTimeout(uploading, 20);
});
~~~
预览效果如下：
