数组转树

// 例如将 input 转成output的形式
let input = [
  {
    id: 1,
    val: "学校",
    parentId: null,
  },
  {
    id: 2,
    val: "班级1",
    parentId: 1,
  },
  {
    id: 3,
    val: "班级2",
    parentId: 1,
  },
  {
    id: 4,
    val: "学生1",
    parentId: 2,
  },
  {
    id: 5,
    val: "学生2",
    parentId: 2,
  },
  {
    id: 6,
    val: "学生3",
    parentId: 3,
  },
];

let output = [
  {
    id: 1,
    val: "学校",
    children: [
      {
        id: 2,
        val: "班级1",
        children: [
          {
            id: 4,
            val: "学生1",
            children: [],
          },
          {
            id: 5,
            val: "学生2",
            children: [],
          },
        ],
      },
      {
        id: 3,
        val: "班级2",
        children: [
          {
            id: 6,
            val: "学生3",
            children: [],
          },
        ],
      },
    ],
  },
];

// 代码实现
function arrayToTree(array) {
  let root = array[0];
  return toTree(null, array);
}

// 传入父节点id，和没有根元素的array
function toTree(parentId, array) {
  let children = [];
  let len = array.length;
  for (let i = 0; i < len; i++) {
    let node = array[i];
    if (node.parentId === parentId) {
      children.push({
        id: node.id,
        val: node.val,
        // 没有child，toTree会返回children初值[],所以不用担心
        children: toTree(node.id, array),
      });
    }
  }
  return children;
}

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