树形结构，每一个加上唯一id

var treeData=[

    {
      label: 'aaa',
      children: [
        { 
          label: 'bbb' 
        },
        { 
          label: 'ccc' 
        },
        { 
          label: 'ddd' 
        }
      ]
    }
  ]

function setId(list, start=1) {
  return list.reduce((id, item) => {
    item.id = id++;
    return Array.isArray(item.children) ? setId(item.children, id) : id;
  }, start);
}

setId(treeData)
console.log(treeData)