简单JS切换代码简化

Question

下面是是自己写的日常普通切换动作，不知道怎么去简化，看着好冗余... 譬如怎么合并prev和next两个事件？委托于control-wrap父元素上？

Live Demo

HTML

<div class="container">
    <div class="box">1</div>
    <div class="box">2</div>
    <div class="box">3</div>
    <div class="box">4</div>
    <div class="box">5</div>
    <div class="box">6</div>
    <div class="box">7</div>
    <div class="box">8</div>
    <div class="box">9</div>
</div>
<div class="control-wrap">
    <span class="prev">prev</span>
    <span class="next">next</span>
</div>

JS