It is made part of a Node.js project by applying the following commands:

mkdir myexpapp
cd myexpapp
git init
npm init -y
npm install express

Resulting in

{
  "name": "myexpapp",
  "version": "1.0.0",
  "description": "",
  "main": "index.js",
  "scripts": {
    "test": "echo \"Error: no test specified\" && exit 1"
  },
  "keywords": [],
  "author": "",
  "license": "ISC",
  "dependencies": {
    "express": "^4.17.1"
  }
}

Look back at the section called “Project Creation - Best Practice”, and expand the above to

{
  "name": "myexpapp",
  "version": "1.0.0",
  "main": "index.js",
  "scripts": {
    "checkpoint": "git add .  && git commit -F - && git push origin master ",
    "pretest": "npm install",
    "test": "node index"
  },
  "keywords": [],
  "author": "Niels Müller Larsen <nmla@iba.dk> (http://dkexit.eu)",
  "license": "ISC",
  "dependencies": {
    "express": "^4.17.1"
  },
  "devDependencies": {},
  "description": ""
}

The minimal, proverbial express application is then

"use strict";
const hostname = "localhost";
const port = Number(process.argv[2]) || 3000;

const express = require("express");
const app = express();

app.get("/", (req, res) => res.send("Hello World!"))

app.listen(port, () => console.log(`Server has started. Navigate to http://${hostname}:${port}/ to use it.`));

Express has an idiosyncracy of what a normal web project architecturally should look like. There's an Express command line tool that implements this. Let us install it as follows. Remember that the -g option, global, makes the tools globally available, ie across projects.

npm install express-generator -g

If you have installed node as a computer wide installation, not purely in your local user part of the file system, you may need to be an administrator to achieve the required permissions. On Linux or OSX this may be done with sudo, on Windows you might need to run cmd in administrator mode. Now, let us see what is possible and what not.

express -h

  Usage: express [options] [dir]


  Options:

        --version        output the version number
    -e, --ejs            add ejs engine support
        --pug            add pug engine support
        --hbs            add handlebars engine support
    -H, --hogan          add hogan.js engine support
    -v, --view <engine>  add view <engine> support (dust|ejs|hbs|hjs|jade|pug|twig|vash) (defaults to jade)
        --no-view        use static html instead of view engine
    -c, --css <engine>   add stylesheet <engine> support (less|stylus|compass|sass) (defaults to plain css)
        --git            add .gitignore
    -f, --force          force on non-empty directory
    -h, --help           output usage information

With that done let us try to generate a skeleton web application.

 express --view=pug demoproject

   create : demoproject/
   create : demoproject/public/
   create : demoproject/public/javascripts/
   create : demoproject/public/images/
   create : demoproject/public/stylesheets/
   create : demoproject/public/stylesheets/style.css
   create : demoproject/routes/
   create : demoproject/routes/index.js
   create : demoproject/routes/users.js
   create : demoproject/views/
   create : demoproject/views/error.pug
   create : demoproject/views/index.pug
   create : demoproject/views/layout.pug
   create : demoproject/app.js
   create : demoproject/package.json
   create : demoproject/bin/
   create : demoproject/bin/www

   change directory:
     $ cd demoproject

   install dependencies:
     $ npm install

   run the app:
     $ DEBUG=demoproject:* npm start

With that under our belt, we shall proceed to see the way we normally build node applications.