为什么下面这种写法会出现问题呢？我只是在len前面加了一个var，len变成全局变量之后就实现不了想要的效果了，求解

             for(var i= 0,var len = oLis.length;i<len;i++){
                 oLis[i].index = i;
                 oLis[i].onclick = function() {
                     for(var n= 0;n<len;n++){
                         oLis[n].className = "";
                         oDivs[n].className = "hide";
                     }
                     this.className = "on";
                     oDivs[this.index].className = "";
                 }
             };