docs: function(start, end, step) { // 用于生成整数数组
              step || (step = 1)
              if (end == null) {
                  end = start || 0
                  start = 0
              }
              var index = -1,
                      length = Math.max(0, Math.ceil((end - start) / step)),
                      result = Array(length)
              while (++index < length) {
                  result[index] = start
                  start += step
              }
              return result
          }