Saturday, April 27, 2013

Caption Captain

Before I write a post about my most recent project, I thought it would be a good idea to write about the thing I did before that. It had a much smaller scope, and I made it so long ago now that I'm in danger of forgetting absolutely everything what I did.

Before I start the explanation, I should just provide a link to the site - http://captioncapta.in. Glad that's out of the way! So Caption Captain is a game that picks one image and three titles at random from reddit, and the goal is to pick the title that the image was submitted with. With a subreddit like Reaction GIFs this is a pretty fun game and an entertaining way of browsing the latest submissions. The game also works with other subreddits, but obviously the ones that are not image-heavy will not work too well, and the captions are sometimes pretty obvious for subreddits like funny or gifs.

The main reason I wanted to make this was both to have a bit of practice with Dojo and Bootstrap, and to see what I could do with a site when I limited myself to having a minimal infrastructure - I wanted to implement everything in pure HTML and JavaScript and have no server-side logic. That means no database, no server to access remote URLs, and no URL routing. The site could be served as a single HTML file, but I split it up a bit for clarity. It's currently running on Amazon S3 so it has minimal cost and maintenance.

This post will probably be light on the code, but I've put up all the source on GitHub so you can follow along by going there.

The first problem I encountered was due to my technology choices. Bootstrap (the JavaScript part at least) is generally written to be used alongside jQuery instead of Dojo. I would also prefer to use jQuery, but I knew I had to use Dojo for another thing I was working on, so I wanted to get at least a little bit of practice with it. Thankfully, some kind soul has done the hard work and re-written Bootstrap's JavaScript modules in a format that works well with Dojo and they creatively named it Dojo Bootstrap. All I wanted to use was Bootstrap's Modal functionality, and with Dojo Bootstrap this was as easy as require-ing the Modal module and putting the right tags into the HTML.

The next problem to solve was thinking about how to get subreddit data. Usually I'd just write some code into the server to query reddit, then return that as part of a site or ajax request, but since I didn't want to actually use a server this was not possible. Luckily, reddit's JSON API supports the usage of JSONP, which means we can call it on the client side and use the response inside a JavaScript function. Using this I made a function that would attempt to get the next image and set of captions, and if there were not left it used JSONP to get some more images and captions from reddit before returning one of them. All of the image loading logic is in imageLoader.js but to summarize - getNextImage is the main function, this will return an image if we have it, otherwise it calls _loadImages. _loadImages calls a set of query functions asynchronously, one for a few different sort orders of the subreddit, and that function (_getDataFromReddit) is a fairly generic JSONP call. Once all of these queries finish, the results are filtered to make sure that the link is an image and that its score isn't too low, then it's separated into a set of images and captions that are ready for use.

The rest of the code and HTML (mainly in index.html and controller.js) is pretty standard scaffolding code so I won't go through most of it, but the last thing I wanted to mention was the solution to the problem of URL routing when not using a server. I wanted to support the selection of different subreddits, but the usual solution of having a unique URL for each subreddit and using URL routes to detect the subreddit would not work in a plain HTML page. However, JavaScript does have access to the full URL, including query string, so all we need to do is redirect to index.html with e.g. ?subreddit=reactiongifs, detect that on page load, and the problem is solved.

So that's it, the main thing I learnt is that I don't really like using Dojo as much as jQuery, at least for the "utility" functionality. I still think it's pretty good for UI work, and the rest of it has improved a lot recently, but it's hard to beat jQuery for things like AJAX and async calls. I also quite enjoyed the challenge of making a single-HTML page, and if I ever think of something else that would work in that form I'll have another go at it. It's just lovely to be able to shove something on S3 and forget about it while it keeps running happily in the background.

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