js实现展开关闭效果

(function (){
var index=document.getElementById("list_cou_zhankai");
var vars=index.getElementsByTagName("var");
var spans=index.getElementsByTagName("span");
var strongs=index.getElementsByTagName("strong");
var dls=index.getElementsByTagName("dl");
var hei=vars[0].offsetHeight;
for(var i=0;i<spans.length;i++){
spans[i].onclick=function zengjia(){
for(var i=0;i<spans.length;i++){
if(this==spans[i]){
if(vars[i].style.overflow=="visible"){
vars[i].style.overflow="hidden";
vars[i].style.height=45+"px";
strongs[i].innerHTML="▼展开";
}else{
vars[i].style.overflow="visible";
vars[i].style.height="auto";
strongs[i].innerHTML="▲关闭";
}
}
}
}
}
})();