In this step, we will be building a simple web app using node.js and the express framework

A short bit about node.js

If you’re here, you probably have some sort of idea what node.js is all about: JavaScript on the server. To some people this is sacrilege (“JavaScript? On my server?”), but it’s actually proven to be quite capable as a server side language.

The crux of node.js is event loop: everything runs in a single thread, and the default I/O methods run asyncronously as to not block the loop. If that all doesn’t make sense, that’s okay.

Getting & Installing node.js

If you’re running Windows or OS X, you can download a package to install node for your system. If you’re on some flavor of Linux, use your package manager of choice. You can find more information about installing via package manager at the node.js github wiki.

A note about node.js versions

node.js (and all npm packages, which we will get to) follow the Semantic Versioning scheme. If that’s TL;DR, the idea is the it follow X.Y.Z for it’s version number, where X is the major version, Y is the minor version and Z is the patch version.

node.js release versioning use the same system as the Linux kernel – even minor versions stable releases, odd minor versions for unstable or development versions. Development will break backwards compatibility, experiment with new APIs that may not make it to stable releases and do other wacky things, so for beginners it’s best to stick with the stable releases for now.

As of writing, the latest stable node.js is v0.6.8. The version supported by heroku’s cedar stack is v0.4.7. For the purposes of this challenge, this shouldn’t be a problem. As an exercise left to the reader, after you finish, try to figure out how to A) run a different version of node.js on heroku, and/or B) figure out how to install node.js v0.4.7 on your system (which may involve building from source!)

Okay, I’ve installed node.js, now what?

As a matter of best practices, it’s good to write your package.json first. Here is an example to get you started:

{
  "name": "hello-node",
  "description": "A tiny little hello world app in node, using express",
  "version": "0.0.1",
  "dependencies": {
    "express": "2.5.x"
  }
}

Not only is this file necessary for heroku, it makes using npm more awesome. For example, you can do:

npm install

and it will install express and all its dependencies into the “node_modules” folder. Go ahead and ls to make sure it’s there, and feel free to explore the directory structure npm created.

Deeper Dive

If you want to learn about all of the things you can include in package.json, enter this into your terminal:

npm help json

Be warned: It’s a lot of stuff. Another, more digestable resource is an article by Charlie Robbins of nodejitsu called ”Package.json dependencies done right”.

Let’s write the thing

Using your favorite text editor (preferably one that has syntax highlighting for JavaScript), create a file called “web.js” and put this in it:

var express = require('express');

var app = express.createServer(express.logger());

app.get('/', function(request, response) {
  response.send('Hello, world.');
});

var port = process.env.PORT || 3000;
app.listen(port, function() {
  console.log('Listening on ' + port);
})

Create another file, call it “Procfile”, and put this inside:

web: node web.js

Make sure to save both those files into your project folder, then type foreman start. If everything goes to plan, you should see something like this:

00:18:11 web.1     | started with pid 97759
00:18:11 web.1     | Listening on 5000

(Notice: your timestamp at the beginning will be different, as well as your pid). Now open up your web browser, point it to http://localhost:5000/ and you should see your friendly web server greeting the world in response!

When you want to stop the server, press Ctrl+C in the terminal.

If everything is working correctly, this would be a great time to make a commit. If you don’t remember how and you’re feeling adventurous, type git into your terminal and read what comes up. If you don’t understand a command, you can type git help followed by the name of the command to get more information. Alternatively, you can always check back in the first task where we set up git.

Wait, something went wrong!

This is a great opportunity to learn how to get help! Copy any error messages you get and put them in the comments, along with what you were trying to do when that happened. You can also try googling those error messages to see if someone has had the same problem. A large part of development is figuring out what went wrong and then figuring out how to solve it – we depend on our peers to help us with both of these things!

(self-)EDITORS NOTES

• should I try to break down “web.js” line by line? Or should I make that some extra credit?
• also, same thing with Procfile and foreman. I feel like this task is really dense already.