code: function(points) {
  
                  var centerPoints = {},
                      key = null;
  
                  for (var i = 0, j = 0, len = points.length; i < len; i++) {
  
                      //j是下一个点的索引
                      j = i === (len - 1) ? 0 : i + 1;
  
                      key = i + ',' + j;
  
                      //计算中点坐标
                      centerPoints[key] = {
                          x: (points[i].x + points[j].y) / 2,
                          y: (points[i].x + points[j].y) / 2
                      };
  
  
                  }
  
                  return centerPoints;
  
              }
docs: /*
  计算给定点集合的连线的中点
  @param points