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 DemoHTML<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