层级数据是有父子关系的数组，示例：

const treeData = [
  {
    id: '1b7e8e98cb1d4a1f81e4fe2dfd9a8458',
    name: '层级1',
    parentId: null,
    children: [
      {
        id: '0d45dd5bb4c14d64a3ab0b738add4b24',
        name: '层级1-1',
        parentId: '1b7e8e98cb1d4a1f81e4fe2dfd9a8458',
        children: [
          {
            id: 'd559c08b408b46e08fc66ad6e653425d',
            name: '层级1-1-1',
            parentId: '1b7e8e98cb1d4a1f81e4fe2dfd9a8458',
          },
          {
            id: '83bdbc6a873842d69b849532c68aa1d2',
            name: '层级1-1-2',
            parentId: '1b7e8e98cb1d4a1f81e4fe2dfd9a8458',
          },
        ],
      },
      {
        id: 'edbaec28dde842a781cdfd9c3df1d6a0',
        name: '层级1-2',
        parentId: '1b7e8e98cb1d4a1f81e4fe2dfd9a8458',
      },
    ],
  },
  {
    id: 'eb6005ef3c634921b20d4dd368934da3',
    name: '层级2',
    parentId: null,
    children: [
      {
        id: 'e8ce379630824bf39e6b16c6c3b103d8',
        name: '层级2-1',
        parentId: 'eb6005ef3c634921b20d4dd368934da3',
      },
    ],
  },
  {
    id: '13052d2aaace4be6928e207199453dfc',
    name: '层级3',
    parentId: null,
  },
];

扁平化数据是一个一维数组，示例：

const array = [
    {
        "id": "1b7e8e98cb1d4a1f81e4fe2dfd9a8458",
        "name": "层级1",
        "parentId": null
    },
    {
        "id": "0d45dd5bb4c14d64a3ab0b738add4b24",
        "name": "层级1-1",
        "parentId": "1b7e8e98cb1d4a1f81e4fe2dfd9a8458"
    },
    {
        "id": "d559c08b408b46e08fc66ad6e653425d",
        "name": "层级1-1-1",
        "parentId": "0d45dd5bb4c14d64a3ab0b738add4b24"
    },
    {
        "id": "83bdbc6a873842d69b849532c68aa1d2",
        "name": "层级1-1-2",
        "parentId": "0d45dd5bb4c14d64a3ab0b738add4b24"
    },
    {
        "id": "edbaec28dde842a781cdfd9c3df1d6a0",
        "name": "层级1-2",
        "parentId": "1b7e8e98cb1d4a1f81e4fe2dfd9a8458"
    },
    {
        "id": "eb6005ef3c634921b20d4dd368934da3",
        "name": "层级2",
        "parentId": null
    },
    {
        "id": "e8ce379630824bf39e6b16c6c3b103d8",
        "name": "层级2-1",
        "parentId": "eb6005ef3c634921b20d4dd368934da3"
    },
    {
        "id": "13052d2aaace4be6928e207199453dfc",
        "name": "层级3",
        "parentId": null
    }
];

层级数据转换成扁平化数据

const generateList = (tree) => {
  let dataList = [];
  const getList = (data, parentId) => {
    for (const item of data) {
      dataList.push({
        id: item.id,
        name: item.name,
        parentId,
      });
      if (item.children) {
        getList(item.children, item.id);
      }
    }
  }
  getList(tree, null);
  return dataList;
};

const array = generateList(treeData);
console.log(array);

找到某一个子元素的所有祖先元素

const getAncestor= (tree, id) => {
  const ancestor = [];
  const getParent = (tree, id) => {
    for (const item of tree) {
      if (item.id === id) {
        ancestor.unshift({ id: item.id, name: item.name });
        return true;
      }
      if (item.children && item.children.length > 0 && getParent(item.children, id)) {
        ancestor.unshift({ id: item.id, name: item.name });
        return true;
      }
    }
    return false;
  };
  getParent(tree, id);
  return ancestor;
};

const child = {
  id: '83bdbc6a873842d69b849532c68aa1d2',
  name: '层级1-1-2',
};
const ancestors = getAncestor(treeData, child.id);
console.log(ancestors);

找到某一个父元素的所有子元素们

const getDeepChildren = (tree) => {
  const array = [];
  const getChildren = (tree) => {
    tree.forEach(({ id, name, children }) => {
      array.push({ id, name });
      if (children) {
        getDeepChildren(tree);
      }
    });
  }
  getChildren(tree);
  return array;
};
const getChildren = (tree, childId) => {
  const array = [];
  const getChildren = (tree, childId) => {
    tree.forEach(({ id, name, parentId, children }) => {
      if (parentId === childId) {
        array.push({ id, name });
        if (children) {
          const allChildren = getDeepChildren(children);
          array.push(...allChildren);
        }
      } else if (children) {
        getChildren(children, childId);
      }
    });
  };
  getChildren(tree, childId);
  return array;
};

const parent = {
  id: '1b7e8e98cb1d4a1f81e4fe2dfd9a8458',
  name: '层级1',
};
const children = getChildren(treeData, parent.id);
console.log(children);