平铺数组转换为树结构

使用场景：当数据结构为平铺时，需要将该结构转换为带有层级的树结构

const getTree = () => {
  const arr = [
    { id: 2, parentId: 0, text: '一级节点' },
    { id: 21, parentId: 2, text: '二级节点' }
  ]
  const idMap = {}
  arr.forEach(item => {
    idMap[item.id] = item
  })
  const result = []
  for (const idMapKey in idMap) {
    if(idMap[idMap[idMapKey].parentId]) {
      if(idMap[idMap[idMapKey].parentId].children) {
        idMap[idMap[idMapKey].parentId].children.push(idMap[idMapKey])
      } else {
        idMap[idMap[idMapKey].parentId].children = [idMap[idMapKey]]
      }
    } else {
      result.push(idMap[idMapKey])
    }
  }
  console.log(result)
}