Mongo connection problems trying to learn basic crud in nodejs mongodb

guys I have the following form:

<!doctype html>
<html lang="en">
    <meta charset="UTF-8">
    <title>Client Data</title>
    <h1>Please fill data in the form below:</h1>
    <form method="POST" action="/post-feedback">
        <label>Name:<input type="text" name="client-name" required></label>
        <label>Email:<input type="text" name="client-email" required></label>
        <label>Comment:<br><textarea name="comment"></textarea></label>
        <input type="submit" value="Submit">
    <a href="/view-feedbacks">View feedbacks</a>

and here is the handler:

var express = require('express');
var path = require('path');
var bodyParser = require('body-parser');
var mongodb = require('mongodb');

var dbConn = mongodb.MongoClient.connect('mongodb://localhost:27017',{ useNewUrlParser: true } );

var app = express();

app.use(bodyParser.urlencoded({ extended: false }));
app.use(express.static(path.resolve(__dirname, 'public')));'/post-feedback', function (req, res) {
    dbConn.then(function(db) {
        delete req.body._id; // for safety reasons
    res.send('Data received:\n' + JSON.stringify(req.body));

app.get('/view-feedbacks',  function(req, res) {
    dbConn.then(function(db) {
        db.collection('feedbacks').find({}).toArray().then(function(feedbacks) {
    }).catch(function(error) {
        res.json({"message": "Hello json"})

app.listen(process.env.PORT || 3000, process.env.IP || '' );

I go into the directory and do node app and the server is running on port 3000 and when I submit the form it responds with the data from the method which seems to work fine. except the app.get method… when you click on the /view-feedbacks in the form it responds with the errror handler I put in the catch “hello json” and the command prompt throws this error:

(node:4312) UnhandledPromiseRejectionWarning: TypeError: db.collection is not a function
    at etc...
(node:4312) UnhandledPromiseRejectionWarning: Unhandled promise rejection. This error originated either by throwing inside of an async function without a catch block, or by rejecting a promise which was not handled with .catch(). (rejection id: 1)
(node:4312) [DEP0018] DeprecationWarning: Unhandled promise rejections are deprecated. In the future, promise rejections that are not handled will terminate the Node.js process with a non-zero exit code.

what does this mean and how do I fix this? Im guessing I dont have a connection to the database or I did something wrong?