数组转树

const testData = [
  { id: 1, parentId: "", name: "第三方" },
  { id: 2, parentId: 1, name: "第三方" },
  { id: 3, parentId: 1, name: "第三方" },
  { id: 4, parentId: 1, name: "第三方" },
  { id: 5, parentId: "", name: "第三方" },
  { id: 6, parentId: "", name: "第三方" },
  { id: 1, parentId: "", name: "第434343方" },
];

1.普通遍历

function listToTree(data) {
  // * 先生成parent建立父子关系
  const obj = {};
  data.forEach((item) => {
    obj[item.id] = item;
  });
  // * obj -> {1001: {id: 1001, parentId: 0, name: 'AA'}, 1002: {...}}
  // console.log(obj, "obj")
  const parentList = [];
  data.forEach((item) => {
    const parent = obj[item.parentId];
    if (parent) {
      // * 当前项有父节点
      parent.children = parent.children || [];
      parent.children.push(item);
    } else {
      // * 当前项没有父节点 -> 顶层
      parentList.push(item);
    }
  });
  return parentList;
}

2.reduce

function array2tree(array) {
  return JSON.parse(JSON.stringify(array)).reduce((pre, next) => {
    const { id, parentId } = next;
    if (pre[parentId]) {
      pre[parentId].children = (pre[parentId].children || []).concat([next]);
    } else {
      if (pre[id]) {
        pre[id] = { ...pre[id], ...next };
      } else {
        pre[id] = next;
      }
    }
    return pre;
  }, {});
}