I keep getting "db.collection is not a function" in the browser This is the MEAN stack

const express = require('express');
const app = express();
const path = require('path');
const bodyParser = require('body-parser');
const routes = require('./api/routes');
require('./api/data/dbconnection.js').open();


app.set('port', 3000);

let server = app.listen(app.get('port'), function() {
    let port = server.address().port;
    console.log('Port ' + port);
});

app.use(express.static(path.join(__dirname, 'public')));

app.use(bodyParser.urlencoded({ extended : false }));

app.use('/api', routes);

let express = require('express');
let routes = express.Router();

let ctrl = require('../controllers/controllers.js');

routes
    .route('/json')
    .get(ctrl.GetAll);

routes
    .route('/json/:ProID')
    .get(ctrl.GetOne);

routes
    .route('/json/new')
    .post(ctrl.profileAddOne);

module.exports = routes;

let dbconn = require('../data/dbconnection.js');
let profileData = require('../data/proData.json');

module.exports.GetAll = function(req, res) {
   let db = dbconn.get();
   let collect = db.collection('profile');

   collect
    .find()
    .toArray(function(err, docs) {
        res
            .status(200)
            .json(docs);
    });
};
module.exports.GetOne = function(req, res) {
    let ProID = req.
    console.log("GET the json");
    res
        .status(200)
        .json( ProID );
};
module.exports.profileAddOne = function(req, res) {
    res
        .status(200)
        .json(req.body);
}

let MongoClient = require('mongodb').MongoClient;
let dburl = 'mongodb://localhost:27017/profileDB';

let _connection = null;

let open = function() {
    MongoClient.connect(dburl, function(err, db) {
        if (err) {
            console.log("DB connection Error");
            return;
        }
        _connection = db;
        console.log("DB connection open", db);
    });
};

let get = function() {
    return _connection;
};

module.exports = {
    open : open,
    get : get
};