获取高度最小的列的下标

function getMinHeightIndex(){

          //假设第一列是最小高度列

          var minHeight = cols[0].offsetHeight;

          var minHeightIndex = 0;//假设的下标

          //遍历五个列 找最小高度

          for( var i = 0 ; i < cols.length ; i++ ){

              if( cols[i].offsetHeight < minHeight ){

                   minHeight = cols[i].offsetHeight;

                   minHeightIndex = i;

              }

          }

          return minHeightIndex;

     }