将扁平JSON数组转换为嵌套结构：基于层级信息的JavaScript实现

const content = [
  { "title": "Item 1", "metaData": { "level": 1, "desc": "Some Desc 1", "displayOnOverview": true }},
  { "title": "Item 2", "metaData": { "level": 2, "desc": "Some Desc 2", "displayOnOverview": true }},
  { "title": "Item 3", "metaData": { "level": 2, "desc": "Some Desc 3", "displayOnOverview": false }},
  { "title": "Item 4", "metaData": { "level": 3, "desc": "Some Desc 4", "displayOnOverview": true }},
  { "title": "Item 5", "metaData": { "level": 1, "desc": "Some Desc 5", "displayOnOverview": true }}
];

[
  {
    "title": "Item 1",
    "metaData": {
      "level": 1,
      "desc": "Some Desc 1",
      "displayOnOverview": true
    },
    "subNav": [
      {
        "title": "Item 2",
        "metaData": {
          "level": 2,
          "desc": "Some Desc 2",
          "displayOnOverview": true
        }
      },
      {
        "title": "Item 3",
        "metaData": {
          "level": 2,
          "desc": "Some Desc 3",
          "displayOnOverview": false
        },
        "subNav": [
          {
            "title": "Item 4",
            "metaData": {
              "level": 3,
              "desc": "Some Desc 4",
              "displayOnOverview": true
            }
          }
        ]
      }
    ]
  },
  {
    "title": "Item 5",
    "metaData": {
      "level": 1,
      "desc": "Some Desc 5",
      "displayOnOverview": true
    }
  }
]

// 初始尝试的代码片段
const root = [];
sideNavData.forEach((node, index) => {
    const nodeLevel = node.metaData.level;

    if (root.length === 0) {
        return root.push(node)
    }

    const previousLevel = root[index - 1].metaData.level; // 这里的root[index - 1]不一定是正确的父节点

    if (previousLevel === nodeLevel) {
        return root.push(node)
    } else {
        return root[index - 1]['subNav'] = node // 错误：这里会直接覆盖，并且可能不是正确的父节点
    }
});

const content = [
  { title: "Item 1", metaData: { "level": 1, "desc": "Some Desc 1", "displayOnOverview": true }},
  { title: "Item 2", metaData: { "level": 2, "desc": "Some Desc 2", "displayOnOverview": true }},
  { title: "Item 3", metaData: { "level": 2, "desc": "Some Desc 3", "displayOnOverview": false }},
  { title: "Item 4", metaData: { "level": 3, "desc": "Some Desc 4", "displayOnOverview": true }},
  { title: "Item 5", metaData: { "level": 1, "desc": "Some Desc 5", "displayOnOverview": true }}
];

/**
 * 将扁平JSON数组转换为嵌套结构
 * @param {Array<Object>} data 包含level信息的扁平JSON数组
 * @returns {Array<Object>} 转换后的嵌套JSON数组
 */
function buildNestedStructure(data) {
  const topLevelItems = []; // 存储所有level 1的顶级节点
  const itemMap = {};       // 存储每个level最近处理过的节点，用于查找父节点

  for (const item of data) {
    // 提取title和metaData，可以根据需要提取更多属性
    const { title, metaData } = item;
    // 创建一个新的节点对象，避免直接修改原始数据
    const newItem = { title, metaData: { ...metaData } }; // 复制metaData以防直接引用问题

    if (metaData.level === 1) {
      // 如果是顶级节点，直接添加到topLevelItems数组
      topLevelItems.push(newItem);
    } else {
      // 如果是子节点，找到其父节点的层级
      const parentLevel = metaData.level - 1;
      // 从itemMap中获取父节点
      const parentItem = itemMap[parentLevel];

      // 检查父节点是否存在，并确保其有subNav数组
      if (parentItem) {
        if (!parentItem.subNav) {
          parentItem.subNav = [];
        }
        // 将当前节点添加到父节点的subNav中
        parentItem.subNav.push(newItem);
      } else {
        // 实际应用中，如果出现level > 1但找不到父节点的情况，可能需要报错或特殊处理
        console.warn(`Warning: Item "${title}" (level ${metaData.level}) has no parent at level ${parentLevel}. It will be orphaned.`);
      }
    }

    // 更新itemMap，将当前newItem存储为当前level的最新节点
    // 这样，后续更深层级的节点可以找到它作为父节点
    itemMap[metaData.level] = newItem;
  }

  return topLevelItems;
}

const output = buildNestedStructure(content);
console.log(JSON.stringify(output, null, 2));