Honza Pokorný

A personal blog

Writing Node.js modules

To say that node.js has enjoyed a great deal of positive publicity in the last few months would most certainly be an understatement. New node.js-related projects are popping up all over the place, and there seems to be this notion that if you aren’t using it you’re not cool enough.

Over the Christmas holidays, I sat down to sort out my photo library and I wanted to make a web photo gallery to share the images with family and friends. Being a mainly Python programmer, I wrote a Python script that will go through all of my photos and create smaller versions and thumbnails of the images that are suitable for the web. I think I have around 1500 images at the moment and it took a good 20 minutes to convert everything using Python Imaging Library.

I was rather frustrated with the performance. I think the reason for the slowness was the fact that the images were processed sequentially, one by one. What if I could modify my program to process more than one image at a time. This would certainly speed by the process. Then I thought about using threads in Python and I think I threw up in my mouth a little.

Then I remembered Node.js. It’s supposed to be all asynchronous and non-blocking. Perfect match. So I wrote a thumbnailer in node.

Essentially, it’s a worker queue that resizes images. You give it a source and destination directories and a number of workers and run it. The total time went from 20 minutes to 2 using about 5 workers. Much better, eh?

I decided to open source the project because I couldn’t find any node.js projects that do something even remotely similar. It’s called node-thumbnail and you can find it on both Github and npmjs.

So what does the API look like?

  source: 'source/path',
  destination: 'dest/path',
  concurrency: 4
  }, function() {
  console.log('All done!');

This article was first published on January 5, 2012. As you can see, there are no comments. I invite you to email me with your comments, criticisms, and other suggestions. Even better, write your own article as a response. Blogging is awesome.