"Express is a minimal and flexible Node.js web application framework that provides a robust set of features for web and mobile applications."

Installation

In the terminal, we'll create and navigate to a folder that will host our server - we're using a folder named my_server located in the home directory:

mkdir ~/my_server
cd ~/my_server

Next step is to initialise your application:

npm init -y

We'll also create the file that will act as the entry point:

touch index.js

To add Express to our app, we'll run the following in the terminal:

npm install express --save

A Simple Server

We'll add a single endpoint that will display a simple "90-10.dev" message. Update index.js as follows:

const express = require('express');
const app = express();
const port = 9010;

app.get('/', (req, res) => {
  res.send('Welcome to 90-10.dev');
});

app.listen(port, () => {
  console.log(`Server started at http://localhost:${port}`);
});

Run

Assuming an index.js file in your current path:

node index.js

Now, if you point our browsers to http://localhost:9010, we'll see a webpage containing the 'Welcome to 90-10.dev' message.

Avoid relaunch

One of the limitations we're going to encounter, is the need to relauch it if changes are afflicted to the source file.

A great utility to overcome this limitation is nodemon. To install it please run the following:

npm install -g nodemon

Launching the server will now be done by replacing node with nodemon:

nodemon index.js

Templating engines

Express supports a lot of templating engines - we're going to use one called pug. To add it to our app:

npm install pug --save

Integrate

Next, we'll integrate it into our app inside index.js - here is the top of it:

const express = require('express');
const app = express();
const port = 9010;

app.set('view engine', 'pug');
app.set('views','./views');
...

Views

You'll notice above that we're going to use a folder named views to store our pug templates. Let's create it together with a index.pug file inside:

mkdir views
touch views/index.pug

First template

Let's add our first view - update views/index.pug:

doctype html
html
   head
      title = "90-10.dev"
   body
      p Welcome to 90-10.dev

Using the template

Back in index.js, let's make use of the new template - the file is listed in its entirety below:

const express = require('express');
const app = express();
const port = 9010;

app.set('view engine', 'pug');
app.set('views','./views');

app.get('/', (req, res) => {
  res.render('index');
});

app.listen(port, () => {
  console.log(`Server started at http://localhost:${port}`);
});

Relaunch the server

nodemon index.js

The reloaded webpage, http://localhost:9010, will now contain HTML as per the template - the noticeable difference is the browser window title now showing: '90-10.dev'.

What next?

The Express website has lots of good resources, amonst them the API reference.