This example assumes you already have node.js installed and are comfortable with JavaScript ES6.
In this example you will build a web page with a single button on it. When this button is clicked this will be recorded in a MongoDB collection. The web page will display an updated count of the number of times the button has been clicked by anyone, anywhere on the web.
Refer to the lecture notes and in-class demonstrations for further information on the technologies and concepts covered here.
Create a folder named node-express-mongo:
mkdir node-express-mongo
Change directory to this folder:
cd node-express-mongo
Run npm init to use the node package manager (NPM) to setup a new node project. You can press enter to accept the default settings, but when you get to entry point: type in server.js.
The node project has now been initialised and you should see a package.json file in your folder. This file stores the project settings and will be updated by npm as you add/remove project dependencies.
Now we need to install express:
npm install express --save
and the MongoDB driver:
npm install [email protected] --save
Note: the above installs a specific version of the mongodb driver. If you wish to use the latest version of the MongoDB driver you will need to modify the code below as described here.
Create an empty file named server.js in your folder. Also, create a folder named public and put empty files named index.html and client.js in that folder. The public folder will store our client-side code. server.js will contain our server-side code.
Project structure:
node-express-mongo/package.json
node-express-mongo/server.js
node-express-mongo/public/index.html
node-express-mongo/public/client.js
Edit your files to contain the following:
index.html
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>Node + Express + MongoDb example</title>
</head>
<body>
<h1>Node + Express + MongoDb example</h1>
<p id="counter">Loading button click data.</p>
<button id="myButton">Click me!</button>
</body>
<script src="client.js"></script>
</html>client.js
console.log('Client-side code running');
const button = document.getElementById('myButton');
button.addEventListener('click', function(e) {
console.log('button was clicked');
});server.js
console.log('Server-side code running');
const express = require('express');
const app = express();
// serve files from the public directory
app.use(express.static('public'));
// start the express web server listening on 8080
app.listen(8080, () => {
console.log('listening on 8080');
});
// serve the homepage
app.get('/', (req, res) => {
res.sendFile(__dirname + '/index.html');
});You can now run your server code using node server.js.
You will need to close (CTRL+C) the server and restart it each time you make changes to server.js. During development this can become a pain. To make this process easier install nodemon, a tool that will monitor your code for changes and automatically restart the server when necessary. To install nodemon:
npm install -g nodemon
You can then run nodemon server.js to run your server and have it reloaded when you make changes.
Try it out by going to http://localhost:8080. When you click the button it should log to the console.
This assumes you have already have access to a server running MongoDB. There are a few options you could use for this:
- Install MongoDB locally on your machine following these instructions. Note: you are required to create a folder
/data/dbon Mac orC:\data\dbon Windows to act as a data store for MongoDB. Once installed you need to havemongodrunning on your machine and listening for connections. You can use Compass to manage the data in MongoDB. You should create database that contains a collection namedclicks. - Use the MongoDB database on the IADT server named daneel. First, use Compass to connect to daneel and create a collection named
clicksunder your database. You should use your student number as username and password (lowercasen). Then use the connection URLmongodb://n000xyz:n000xyz@daneelfrom your JavaScript code (wheren000xyzis your student number). - Create a free account at mLab. Once you have created an account you should created a database containing a collection named
clicksand add a new user with access to this collection. Note: you will be unable to access mLab from within IADT as traffic is blocked by the firewall 😞. Again, you can test that this is working by connecting using Compass.
Once you have got one of the above setup and verified that you can connect using Compass, you can proceed to connecting from your server-side JavaScript code.
Require the mongodb module and add the MongoDB connection code to server.js:
console.log('Server-side code running');
const express = require('express');
const MongoClient = require('mongodb').MongoClient;
const app = express();
// serve files from the public directory
app.use(express.static('public'));
// connect to the db and start the express server
let db;
// ***Replace the URL below with the URL for your database***
const url = 'mongodb://user:password@mongo_address:mongo_port/databaseName';
// E.g. for option 2) above this will be:
// const url = 'mongodb://localhost:21017/databaseName';
MongoClient.connect(url, (err, database) => {
if(err) {
return console.log(err);
}
db = database;
// start the express web server listening on 8080
app.listen(8080, () => {
console.log('listening on 8080');
});
});
// serve the homepage
app.get('/', (req, res) => {
res.sendFile(__dirname + '/index.html');
});If you have done this correctly there will be no errors from Node.
Let's modify client.js so that it sends a HTTP POST request to the http://localhost:8080/clicked API endpoint on our server. Note: we are using fetch() here as covered in a recent lecture, we could also use XHR, jQuery, await + async, or a similar means of making an asynchronous request.
client.js
console.log('Client-side code running');
const button = document.getElementById('myButton');
button.addEventListener('click', function(e) {
console.log('button was clicked');
fetch('/clicked', {method: 'POST'})
.then(function(response) {
if(response.ok) {
console.log('Click was recorded');
return;
}
throw new Error('Request failed.');
})
.catch(function(error) {
console.log(error);
});
});But... the http://localhost:8080/clicked API endpoint does not exist yet on our server. We can set up this endpoint (or route) by adding the following to the end of server.js.
// add a document to the DB collection recording the click event
app.post('/clicked', (req, res) => {
const click = {clickTime: new Date()};
console.log(click);
console.log(db);
db.collection('clicks').save(click, (err, result) => {
if (err) {
return console.log(err);
}
console.log('click added to db');
res.sendStatus(201);
});
});Note that this has added a POST route at http://localhost:8080/clicked. The anonymous callback supplied uses Mongo's save() method to add a new document to the collection containing the current date & time.
If you try this out and view the content of your database (via a tool like Compass) you will see these new documents appearing in your clicks collection.
Add a new route to the end of server.js:
// get the click data from the database
app.get('/clicks', (req, res) => {
db.collection('clicks').find().toArray((err, result) => {
if (err) return console.log(err);
res.send(result);
});
});This adds a GET endpoint at http://localhost:8080/clicks which will return an array containing all the documents in the database, i.e. records of every time the button was clicked. To test this you can just visit http://localhost:8080/clicks in a browser (make sure you have server.js running in node).
Next we will consume (use) this API endpoint from our client-side code. We will add a setInterval() function that will poll the server every second, retrieve all the click data and then display the number of clicks in the UI.
Add this to the end of client.js:
setInterval(function() {
fetch('/clicks', {method: 'GET'})
.then(function(response) {
if(response.ok) return response.json();
throw new Error('Request failed.');
})
.then(function(data) {
document.getElementById('counter').innerHTML = `Button was clicked ${data.length} times`;
})
.catch(function(error) {
console.log(error);
});
}, 1000);Done 🙌 ! The webpage should now update every second based on the number of clicks recorded in the database. This will record total clicks from all users, across multiple sessions!
But... there is some lag between the button press and the webpage updating. Why? Can you improve this?
Final versions of the three key files are below.