code: function range (start, stop, step) {
    var index, len
    var result = []
    var args = arguments
    if (args.length < 2) {
      stop = args[0]
      start = 0
    }
    index = start >> 0
    len = stop >> 0
    if (index < stop) {
      step = step >> 0 || 1
      for (; index < len; index += step) {
        result.push(index)
      }
    }
    return result
  }
docs: 序号列表生成函数
  
  @param {Number} start 起始值
  @param {Number} stop 结束值
  @param {Number} step 自增值
  @return {Object}