Mongo-atlas connection : ReferenceError: client is not defined - mongodb

Question

when trying to connect to the mongo atlas I'm getting the error "ReferenceError: client is not defined".
Console's erro :
const db = client.db('coneccao-teste');
ReferenceError: client is not defined
See below my NodeJs code with the configuration of the Express server and mongo-atlas connection.
Have you sugestion ?
thanks!
const express = require('express');
const app = express();
const router = express.Router();
const MongoClient = require('mongodb').MongoClient;
const ObjectId = require('mongodb').ObjectId;
const port = 3000;
const mongo_uri = 'mongodb+srv://rbk:******-#cluster0-5zvdy.mongodb.net/coneccao-teste?retryWrites=true';
const db = client.db('coneccao-teste');
const collection = db.collection('inicio');
MongoClient.connect(mongo_uri, { useNewUrlParser: true })
.then(client => {
const db = client.db('coneccao-teste');
const collection = db.collection('inicio');
app.listen(port, () => console.info(`REST API running on port ${port}`));
}).catch(error => console.error(error));
// add this line before app.listen()
app.locals.collection = collection;
app.get('/', (req, res) => {
const collection = req.app.locals.collection;
collection.find({}).toArray().then(response => res.status(200).json(response)).catch(error => console.error(error));
});
app.get('/:id', (req, res) => {
const collection = req.app.locals.collection;
const id = new ObjectId(req.params.id);
collection.findOne({ _id: id }).then(response => res.status(200).json(response)).catch(error => console.error(error));
});
app.listen(port);

Answer 1

regarding your second problem the collection is just not defined.
when you declare:
app.locals.collection = collection;
your mongo connection has probably not connected yet meaning that collection is undefined at that point
insert this declaration after the connection is established and before you start listening with ur app:
MongoClient.connect(mongo_uri, { useNewUrlParser: true })
.then(client => {
const db = client.db('coneccao-teste');
const collection = db.collection('inicio');
app.locals.collection = collection;
app.listen(port, () => console.info(`REST API running on port ${port}`));
}).catch(error => console.error(error));
now the collection is guaranteed to be defined the way you expect it to be when starting your app.