Setting up Node and Express


I’ve been talking to a few people lately about how I build web applications. There’s no single right-way of doing it, but here’s my workflow, split into small blog posts you can follow.

First of all, let’s create a web server using node.js.

Setting Up

As a prerequisite, install node.js. You can download the latest version here.

You’ll also need somewhere on your computer to save the files you’re going to create. Using your console, navigate to the correct place, and create a directory:

> mkdir my-app
> cd my-app

If you’re planning on using git, you can also create a .gitignore file. Just add node_modules to the ignore list.

Installing Express

Express is a framework which makes it easy to write web servers in node.

All the files you need are stored in the npm repository. This is database of packages for node.js. You’ll find express here.

To install express, you just need to type:

> npm install express

You’ll notice that a node_modules directory is created, with an express sub-directory. This contains all the express code, as well as its dependencies.

Hello World

Now let’s create a basic web server and start listening on port 8080 for web requests.

You need to create a JavaScript file, you can use your favourite text editor. Let’s call it server.js:

// load the express package

var express = require('express');

// create an express application
var app = express();

// handle GET requests at /
app.get('/', function(req, res){

// respond with plain text
res.send('hello world');
});

// start listening on port 8080
app.listen(8080);

Some things to note about what we’ve written:

  1. The express package can be used to create multiple web servers listening on different ports, which is why we need to call express() to create an instance of an application.
  2. We call app.get(...) to register a route that listens to GET requests that match the supplied path. You can also call app.post(), app.put() etc… or app.all().
  3. When registering a route, you supply a function which gets called every time a matching request is received. The function should have req and res arguments, which represent the request and response data respectively.
  4. You must tell the application which port to listen on to start the web server.

Let’s fire up the application, and make sure it works. To do this, call node, passing our script file as the first argument:

> node server.js

Now point your browser to http://localhost:8080/ and you should see hello world.

Package.json

It is a good idea to create a package.json file. Its not necessary, but its useful for keeping track of the packages your application uses.

To create one, run:

> npm init

You can just go with all the default options, or set the values if you want.

You can run npm init at any point, it’ll figure out what packages you’ve already included.

This will create a package.json file.

When adding further packages, if you add the --save option, npm updates the package.json file so it keeps it up to date. i.e.

> npm install PACKAGE_NAME --save

When you want to run your app on another machine, you can just copy over your JavaScript and your package.json file (without copying all the packages in node_modules directory). You can then run npm install to restore all the modules in one go.