需求是通过el-tree做一份组织架构的更换部门
需要获得最底层的部门的id，和从上累计父部门的id

在初始化拿数据的时候
先递归遍历判断是否是下面有没有子部门
有的话累计id，同时记录父部门下有几个子元素，要重复赋值

赋值到最后一个子元素后要清空父元素，同时传入最上级的id，因为已经被清空了，所有最先记录了

let father = [] // 暂存父元素id
let indexNow = 0 // 记录当前子元素第几个
let indexNum = 0 // 记录父元素下有几个子元素
let companyId = '' // 记录总公司id
let index = 0 // 判断是不是第一个总公司


function recursive(departmentMenuList) {
  if (index === 0) {
    companyId = departmentMenuList[0].departmentId
  }
  index++
  for (var i = 0; i < departmentMenuList.length; i++) {
    if (departmentMenuList[i].childList) {
      indexNum = departmentMenuList[i].childList.length
      father.push(departmentMenuList[i].departmentId)
      departmentMenuList[i].departmentId = null
      recursive(departmentMenuList[i].childList)
    } else {
      departmentMenuList[i].father = father
      indexNow++
      if (indexNum === indexNow) {
        father = []
        father.push(companyId)
        indexNow = 0
        indexNum = 0
      }
    }
  }
}