for-in 的坑

　　for-in 循环的下标为字符串,不是数字

   var ar=[13,2,13,14];
  function isSort(ar){
    for(var i in ar){
      console.log(i+':'+ar[i],i+1+':'+ar[i+1]);
      if(ar[i]>ar[i+1]){
        return -1;
      }
    }
    return 1;
  }
  console.log(isSort(ar));

结果: