形成树结构 ​

/**
 * 递归查找，获取children
 */
const getChildren = (data, result, pid) => {
  for (const item of data) {
    if (item.pid === pid) {
      const newItem = { ...item, children: [] };
      result.push(newItem);
      getChildren(data, newItem.children, item.id);
    }
  }
};

/**
 * 转换方法
 */
const arrayToTree = (data, pid) => {
  const result = [];
  getChildren(data, result, pid);
  return result;
};

function arrayToTree(items) {
  const result = []; // 存放结果集
  const itemMap = {}; //
  for (const item of items) {
    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;
}

function toTree(arr, rootId) {
  let obj = {};
  let tree = [];
  for (let i of arr) {
    const { id, pid } = i;
    if (!obj[id]) {
      obj[id] = {
        // ...i,
        children: [],
      };
    }
    obj[id] = {
      ...i,
      children: obj[id].children,
    };
    if (pid === rootId) {
      tree.push(obj[id]);
    } else {
      if (!obj[pid]) {
        obj[pid] = {
          children: [],
        };
      }
      obj[pid].children.push(obj[id]);
    }
  }
  return tree;
}