code: function randTime (startTime, endTime) {
    let secStart = new Date(startTime).getTime() / 1000
    let secDiff = 0
    if (secStart < 0) {
      secDiff = new Date(endTime) / 1000 + Math.abs(secStart)
    } else {
      secDiff = ~~((new Date(endTime) - new Date(startTime)) / 1000)
    }
    let randSec = tools.rnd(0, secDiff)
    let resultSec = (new Date(startTime)).getTime() + randSec * 1000
    return new Date(resultSec).date2Str()
  }
docs: 在某一时间段内随机生成日期,"2013-02-15 21:00:00"