数组

// 扁平的
var flattenData =[{
    id: root,
    name: 'root',
}, {
    id: 2,
    name: '1-1',
    parentId: 1
}, {
    id: 3,
    name: '1-1-1',
    parentId: 2
}, {
    id: 4,
    name: '1-2',
    parentId: 1
}, {
    id: 5,
    name: '1-2-2',
    parentId: 4
}, {
    id: 6,
    name: '1-1-1-1',
    parentId: 3
}]

树形结构对象

[
  {
    "id": 'root',
    "name": 'root',
    "parentId": '',
    "children": [
      {
        "id": 2,
        "name": "1-1",
        "parentId": 1,
        "children": [
          {
            "id": 3,
            "name": "1-1-1",
            "parentId": 2,
            "children": [
              {
                "id": 6,
                "name": "1-1-1-1",
                "parentId": 3
              }
            ]
          }
        ]
      },
      {
        "id": 4,
        "name": "1-2",
        "parentId": 1,
        "children": [
          {
            "id": 5,
            "name": "1-2-2",
            "parentId": 4
          }
        ]
      }
    ]
  }
]

数组转成树形结构

/**
   * fieldName 子集的字段名
   * pid 父ID
   * result {Array}
   */
export function listConvertTree (list, pid, fieldName) { // 生成树结构
  const result = []
  let temp = []
  for (let i = 0; i < list.length; i++) {
    if (list[i].parentId === pid) {
      const obj = { ...list[i] }
      temp = listConvertTree(list, list[i].id, fieldName)
      if (temp.length > 0) {
        obj[fieldName] = temp
      }
      result.push(obj)
    }
  }
  return result
}

listConvertTree(flattenData,'','children');

树形结构转成数组

export function TreeConvertList (tree, pId, fieldName) { // 生成扁平数组
  const temp = [] // 设置临时数组，用来存放队列
  const result = [] // 设置输出数组，用来存放要输出的一维数组
  temp.push(tree)
  // 首先把根元素存放入out中
  let pid = pId
  const obj = deepCopy(tree)
  obj.parentId = pid
  delete obj[fieldName]
  result.push(obj)
  // 对树对象进行广度优先的遍历
  while (temp.length > 0) {
    const first = temp.shift()
    const children = first[fieldName]
    if (children && children.length > 0) {
      pid = first.id
      const len = first[fieldName].length
      for (let i = 0; i < len; i++) {
        temp.push(children[i])
        const obj = deepCopy(children[i])
        obj.parentId = pid
        delete obj[fieldName]
        result.push(obj)
      }
    }
  }
  return result
}
// 深拷贝
function deepCopy (obj) {
  // 深度复制数组
  if (Object.prototype.toString.call(obj) === '[object Array]') {
    const object = []
    for (let i = 0; i < obj.length; i++) {
      object.push(deepCopy(obj[i]))
    }
    return object
  }
  // 深度复制对象
  if (Object.prototype.toString.call(obj) === '[object Object]') {
    const object = {}
    for (const p in obj) {
      object[p] = obj[p]
    }
    return object
  }
}
listConvertTree(list,'','children');