/**
*下单框原生js插件
* dropdown作为元素class属性的属性值作用在需要添加下拉框效果的元素上
*example:
   dropdown meonetwothree
     四季
     春
     夏
     秋
     冬
  <script src="dropdown.js"></script>
**/
var dropdowns = document.getElementsByClassName("dropdown");
Array.prototype.slice.call(dropdowns,0).forEach(function(item,index){
  var dropdown = item;
  var lis = Array.prototype.slice.call(dropdown.children,0);
  lis.forEach(function(item,index){
    item.setAttribute("style","display:none");
  })
  dropdown.firstElementChild.removeAttribute("style");
  dropdown.onclick = function(){
    lis.forEach(function(item,index){
      var value = item.style.display;
      if(value=="none"){
        item.setAttribute("style","display:visibility");    
      }else{
        item.setAttribute("style","display:none");
        dropdown.firstElementChild.removeAttribute("style");
      }
    })
  }
});