TypeError：更改爲NodeJS時，將圓形結構轉換爲JSON異步等待

Question

我最近了解了NodeJS異步/等待。更改我的代碼，使其更清晰，更易於閱讀。

• 升級到NodeJS 8.2.1。
• MongoDB的2.2.30
• 快遞4.1.4

代碼如下所示：

var express = require('express'); 
    var router = express.Router(); 
    var MongoClient = require('mongodb').MongoClient; 
    var assert = require('assert'); 
    var url = process.env.mongo; 


    /* GET home page. */ 
    router.get('/', async function(req, res, next) { 
     try{ 
     let db = await MongoClient.connect(url); 
     let col = await db.collection('product'); 
     let documents = await col.find(); 
     return res.send(documents) 
     }catch(err){ 
     console.log(err) 
     } 

    }); 


module.exports = router; 

這個錯誤有問題，

TypeError: Converting circular structure to JSON 
at JSON.stringify (<anonymous>) 
at stringify (/home/edmondtm/test-async/node_modules/express/lib/response.js:1064:12) 
at ServerResponse.json (/home/edmondtm/test-async/node_modules/express/lib/response.js:243:14) 
at ServerResponse.send (/home/edmondtm/test-async/node_modules/express/lib/response.js:152:21) 
at /home/edmondtm/test-async/routes/index.js:15:16 
at <anonymous> 
at process._tickCallback (internal/process/next_tick.js:188:7) 

注：沒有問題，如果更改： let documents =等待col.find（）;到 let documents = await col.findOne（）;

希望有人能幫助我。

Answer 1

嘗試 let documents = await col.find().toArray()

col.find()返回遊標而someCursor.toArray()返回一個承諾。