Node.js Jumpstart

In a nutshell, Node is a Javascript framework for building network apps. Network apps are broader in scope than webapps. They don't need to run on HTTP, thus freeing you to write lower level tools. Node doesn’t necessarily have to be part of your core app, and in many cases, it makes for a good fit for writing some of the support functions for your webapp. I'll cover the basics of getting Node setup, some event driven programming, and some miscellaneous Node goodies.

To get started, you can grab the latest Node release from Github. They have good installation instructions, but for the truly uninitiated Mac users, you can install it via homebrew:

brew install node

Once you have Node, you can try it out with an interactive session much like irb. Run node with no arguments:

node
> console.log('hello world')
hello world

Node's biggest core idea is evented I/O. Instead of blocking and waiting for I/O to finish, Node will start I/O, and execute a callback when data is actually ready. On top of reading and writing requests and responses, we spend a lot of time doing I/O when we fetch data from a datastore, or make external requests to other APIs. With Node, we save that wasted blocking time to do actual useful work.

Let's compare a really simple file I/O operation to compare Ruby to Node. Here's a simple Ruby script that will read a file 3 times and print when it finishes, and also print "doing something important".

(1..3).each do |i|
  contents = File.read('foo.txt')
  puts "#{i}. Finished reading file"
  puts "#{i}. doing something important..."
end

We also print out the loop counter to see the order the statements were run. The output is unsurprising:

1. Finished reading file
1. doing something important...
2. Finished reading file
2. doing something important...
3. Finished reading file
3. doing something important...

Now let's look at the Node equivalent of the same script:

var fs = require('fs');
for (var i=1; i<=3; i++) {
  fs.readFile('presentation.key', function(err, data) {
    console.log(i + ". Finished reading file");
  });
  console.log(i + ". doing something important...");
}

What's interesting in this code is the callback we use with the readFile method. By having a callback on this I/O action, readFile will immediately return when called, which allows "doing something important" to be run before the I/O actually completes. When the file is finished reading, then we invoke the callback. Here's the output for the Node script:

1. doing something important...
2. doing something important...
3. doing something important...
4. Finished reading file
4. Finished reading file
4. Finished reading file

Were you surprised by the loop counter 4 in the results? This is one of those subtle "gotcha's" that takes time to get used to. Because the callback is invoked long after the loop is finished, the loop counter variable 'i' has been incremented to 4.

The community for Node is growing, and there is already a large number of non-blocking libraries that are Node friendly. Many of these can be used to build diagnostic and metrics tools for supporting your site. If your site has a need for push notifications or uses AJAX to poll for updates, you can also use Node to handle those features on your site. A few fun examples of apps built with Node include StatsD, Hummingbird Analytics, and Node Wargames.

That covers a brief introduction to Node. I leave you with a quote from the creator of Node that I'm a fan of. He says: