扁平结构转换为树结构

let list = [
        {
    
          id: 1,
          label: "1",
          pid: 0,
        },
        {
    
          id: 11,
          pid: 1,
          label: "1-1",
        },
        {
    
          id: 111,
          pid: 11,
          label: "1-1-1",
        },
        {
    
          id: 2,
          label: "2",
          pid: 0,
        },
        {
    
          id: 22,
          pid: 2,
          label: "2-2",
        },
      ];

      function tranListToTreeData(list, rootValue) {
    
        var arr = [];
        list.forEach((item) => {
    
          if (item.pid === rootValue) {
    
            // 找到之后 就要去找 item 下面有没有子节点
            const children = tranListToTreeData(list, item.id);
            if (children.length) {
    
              // 如果children的长度大于0 说明找到了子节点
              item.children = children;
            }
            arr.push(item); // 将内容加入到数组中
          }
        });
        return arr;
      }
      let result = tranListToTreeData(list, 0);
      // 转换后的list树结构为
      [{
    
          id: 1,
          pid: 0,
          label: "1",
          children: [{
    
              id: 11,
              pid: 1,
              label: "1-1",
              children: [{
    
                  id: 111,
                  pid: 11,
                  label: "1-1-1",
              }]
          }]
      },{
    
          id: 2,
          pid: 0,
          label: '2',
          children: [{
    
              id: 22,
              pid: 2,
              label: '2-2'
          }]
      }]