11

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

    if (!itemMap[id]) {
      itemMap[id] = {
        children: [],
      }
    }

    itemMap[id] = {
      ...item,
      children: itemMap[id]['children']
    }

    const treeItem =  itemMap[id];

    if (parentId == -1) {
      result.push(treeItem);
    } else {
      if (!itemMap[parentId]) {
        itemMap[parentId] = {
          children: [],
        }
      }
      itemMap[parentId].children.push(treeItem)
    }

  }
  return result;
}