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Where do I connect my mongodb Atlas to my react app?

I am building a React app with node.js with mongodb Atlas database. I have created the mongodb Atlas cluster and need to connect it to the React app. The mongodb documentation says to use this code
var MongoClient = require('mongodb').MongoClient;
var uri = "mongodb+srv://kay:myRealPassword#cluster0.mongodb.net/test";
MongoClient.connect(uri, function(err, client) {
const collection = client.db("test").collection("devices");
// perform actions on the collection object
client.close();
});
But - I'm not exactly sure where in my React app it should go. I am using react-router-dom and most places I put it breaks the app. Any ideas?

This code is designed to be used on server side of your app. As You've mentioned You have Node.js server, so put it there and use database connection to serve your data to the React client app.
For example, You can send some data to client when your server receives HTTP request with some endpoint.
Here is nice tutorial for that :)

Database connection works in node.js file but not in script tags

I'm trying to connect to my MongoDB database (or to the server actually MongoLab), it works fine when I have the code in name.js file but it doesn't work when I have it in HTML file inside <script> tags.
Also, I only have those 2 files in my folder, and I'm using Cloud9 framework.
This is my JavaScript code:
// JavaScript File
var MongoClient = require('mongodb').MongoClient;
var url = "x";
MongoClient.connect(url, function(err, db) {
if (err) throw err;
var dbo = db.db("mkndb");
var myobj = { name: "Company Inc", address: "Highway 37" };
dbo.collection("test").insertOne(myobj, function(err, res) {
if (err) throw err;
console.log("1 document inserted");
db.close();
});
});
Thank you

The package mongodb you are requiring is a node.js package, it runs only on the server side and not in the browser.
To access a MongoDB on the client side, you can use the REST webservice.
It allows rudimentary queries through XmlHttpRequests.
To enable it, you have to start mongod with the --rest parameter.
Then you can then query it like this:
http://127.0.0.1:28017/someDatabase/someCollection/?filter_name=someFilter

You seem to be using the Mongodb node client. Inserting the script in html page with tags would not work in the same way as you expect. You have few ways to achieve what you are looking for :
1. You can build a nodejs server component which can handle the requests from browser application. The nodejs server then interacts with mongodb and respond. This again can be achieved in few ways.
a. Deploy nodejs in Lambda. Mode details here - https://docs.aws.amazon.com/cloud9/latest/user-guide/lambda-functions.html . You can then connect from the browser as given here - https://docs.aws.amazon.com/sdk-for-javascript/v2/developer-guide/browser-invoke-lambda-function-example.html
b. Deploy in EC2
2. If you do not want to build/deploy the node.js server, try using the mLab Data API. (http://docs.mlab.com/data-api/) . This works only for this special case where you are trying to connect to MongoLab

Nodejs Desktop app with electron starting server when app is launched

Am building my app with electron and nodejs together with express server.
What am trying to achieve is create a desktop app with angular2 handling the routing together with express
Now on my local developenment i have to start the server (express) so that i can connect to the database, so i have the following that connects to the database
var mysql = require('mysql');
var connection = mysql.createConnection({
host : 'localhost',
user : 'root',
password : 'your-password',
database : 'cloudprint'
});
connection.connect(function(err){
if(!err) {
console.log("Database is connected ... nn");
} else {
console.log("Error connecting database ... nn");
}
});
THe above is run on a server.js which i start on the commandline through
npm server.js
Now am abit confused on how i can reuse the above in my app, since when a person installs the app he will not require to have to start server.js from commandline,
How should i approach this during production time.

To connect create-react-app reactJs with mysql

I have problem in connecting my create-react-app with mysql using npm.
Its working in nodejs when i tried seperately without npm. But, When i trying to connect using npm install mysql, It throws me an error...
TypeError: http.IncomingMessage is undefined
./node_modules/express/lib/request.js
Here is my code:
var express = require('express');
var mysql = require('mysql');
var connection =mysql.createConnection({
host: 'localhost',
user: 'user',
password: '',
database: 'reactproject'
});
connection.connect(function(err){
if(!err) {
console.log("Database is connected ... nn");
} else {
console.log("Error connecting database ... nn");
}
});

This will not work from react-app, since react code will run from client side.
You should use my-sql connection in different app and run in different port and call as api connection.
Thanks.

Adding from an #ashik answer is correct, but if you still want to use MySQL and reactjs simultaneously, you can start by creating your own boilerplate, there you can use MySQL on the server side and create APi/web service without having to separate the APi server and client projects reactjs.

Why socketIO call too much connections?

I created my Socket server with Express, SocketIO and Redis
server.js
var app = require('express')();
var server = require('http').Server(app);
var io = require('socket.io')(server);
var redis = require('redis');
server.listen(8890, function (e) {
console.log(e);
});
io.on('connection', function (socket) {
console.log("new client connected");
var redisClient = redis.createClient();
redisClient.subscribe('message');
redisClient.on("message", function(channel, message) {
console.log("mew message in queue "+ message + "channel");
socket.emit(channel, message);
});
socket.on('disconnect', function() {
redisClient.quit();
});
socket.on('connect_error', function() {
redisClient.quit();
});
});
From command line, I run node server.js. Its worked.
I also created a html file to connect to that server.
From Browser Console, I run io.connect('http://localhost:8890'). I got as the result
As I see, too much connections (requests).
What happens? What wrong from my code?

You have mismatched client and server versions causing the initial connection to fail and the older client is dumb enough to just keep trying over and over again. If you are using 2.0.4 on the server, then you must use that version for the client too. If you serve the client version directly from your server with:
<script src="http://localhost:8890/socket.io/socket.io.js"></script>
Then, the socket.io server will automatically give you the right client version.
Or, you can manually link to the right version on your CDN such as https://cdnjs.cloudflare.com/ajax/libs/socket.io/2.0.4/socket.io.js. But client and server versions MUST match.
The advantage of getting the client directly from your own server is that anytime you update your server version of socket.io, the client version will automatically be upgraded for you and kept in perfect sync since the matching client version is built into the server version.