我无法删除mongodb中的数据

Question

我做路由器。我做了插入，获取和更新路线。所有这些都符合预期。像所有这些记号一样，我也做了“删除”路由，但是删除不起作用。我该怎么办？

index.js：

var express = require("express");
var router = express.Router();
let mongo = require("mongodb").MongoClient;
let objectId = require("mongodb").ObjectID;
let assert = require("assert");

let url = "mongodb://localhost:27017/test";
/* GET home page. */
router.get("/", function(req, res, next) {
  res.render("index");
});
router.post("/delete", (req, res, next) => {
  let id = req.body.id;
  mongo.connect(url, (err, db) => {
    assert.equal(null, err);
    db.collection("testdata").deleteOne(
      { _id: objectId(id) },
      (err, result) => {
        assert.equal(null, err);
        console.log(id, "Item deleted"); // id displayed as 'underfined'
        db.close();
      });
  });
});