// 转换访问来源地址
const getLocation = href => {
  const a = document.createElement('a')
  a.href = href
  return a
}
​
// 统计访客数据
const visitorStatistics = () => {
  const referrer = getLocation(document.referrer)
  const hostname = referrer.hostname
​
  return new Promise(resolve => {
    const query = new AV.Query('Visitor')
    const Visitor = AV.Object.extend('Visitor')
    query.equalTo('referrer', hostname)
    query
      .first()
      .then(res => {
        // 存在则增加访问次数
        if (res) {
          res
            .increment('time', 1)
            .save(null, { fetchWhenSave: true })
            .then(() => resolve())
            .catch(console.error)
        } else {
          // 不存在则新建
          const newVisitor = new Visitor()
          newVisitor.set('referrer', hostname)
          newVisitor.set('time', 1)
          newVisitor
            .save()
            .then(() => resolve())
            .catch(console.error)
        }
      })
      .catch(console.error)
  }).catch(console.error)
}