tree to list and list to tree

demo.ts

  const toList: any = ({ childrens, ...data }: any) => {
    return (childrens || []).reduce(
      (prev: any[], { childrens, ...curr }: any) => {
        if (childrens?.length) {
          prev = prev.concat(recursionFlatten({ childrens, ...curr }))
        } else {
          prev = prev.concat(curr)
        }
        return prev
      },
      [data],
    )
  }

  const toTree = (data: any[]) => {
    const idMapping = data.reduce((prev, curr, index) => {
      prev[curr.departmentid] = index
      return prev
    }, {})

    let root
    data.forEach((item) => {
      if (item.parentid === 0) {
        root = item
        return
      }

      const parent = data[idMapping[item.parentid]]
      parent.childrens = [...(parent.childrens || []), item]
    })

    return root
  }

  const flattenData = toList(data[0], data[0].childrens)
  console.log(flattenData)

  console.log('toTree:', toTree(flattenData))