数组转树

const list = [
  {id: 1, name: '部门1', pid: 0},
  {id: 2, name: '部门1-1', pid: 1},
  {id: 3, name: '部门1-2', pid: 1},
  {id: 4, name: '部门1-1-1', pid: 2},
  {id: 5, name: '部门1-2-1', pid: 3},
  {id: 6, name: '部门2', pid: 0},
  {id: 7, name: '部门2-1', pid: 6},
  {id: 8, name: '部门3', pid: 0},
]

递归实现

// 递归查找获取子节点
const getChild = (list, result, pid) => {
  for(const item of list) {
    if(item.pid === pid) {
      const newItem = { ...item, children: [] };
      result.push(newItem);
      getChild(list, newItem.children, item.id);
    }
  }
}
// 调用递归实现
const listToTree = (list, pid) => {
  const result = [];
  getChild(list, result, pid);
  return result;
}
listToTree(list, 0)

Map对象实现

const listToTree = (list) => {
  // 最终树形结构输出的结果
  const result = [];
  const itemMap = {};
  for(const item of list) {
    const id = item.id;
    const pid = item.pid;
    if(!itemMap[id]) {
      itemMap[id] = {
        children: [],
      };
    }
    itemMap[id] = {
      ...item,
      children: itemMap[id]["children"],
    };
    const treeItem = itemMap[id];
    if(pid === 0) {
      result.push(treeItem)
    } else {
      if(!itemMap[pid]) {
        itemMap[pid] = {
          children: []
        }
      }
      itemMap[pid].children.push(treeItem);
    }
  }
  return result;
}

listToTree(list, 0)

filter实现

const listToTree = (list, key) => {
  const tree = list.filter(function(parent) {
    // 返回每一项得的子级数据
    const branchArr = list.filter((child) => parent.id === child[key]);
    parent.children = [];
    // 如果存在子级，则给父级添加一个children属性并赋值
    if (branchArr.length > 0) {
      parent.children = branchArr;
    }
    // 返回第一层
    return parent[key] == 0;
  });
  return tree;
}
// 传入原始数据和父级pid的key
listToTree(list, 'pid')