Function getScrollPercent

getScrollPercent(direction?, dom?): number
获取滚动条百分比
Parameters
- direction: "X" | "Y" = 'Y'
  X/Y 轴的进度条
- dom: any = document.documentElement
  元素
Returns number
Example
```
getScrollPercent(document.documentElement, 'Y'); /// 0.581134549876
```