Aggregate.end(): Promise<Object>

    示例代码

    2. db.collection('books').aggregate()
    3.     // 按 category 字段分组
    4.     _id: '$category',
    6.     avgSales: $.avg('$sales')
    7.   })
    8.     success: function(res) {
    10.     },
    11.     fail: function(err) {
    12.       console.error(err)