Wherein I, Matthew Wilson, write about development.

CoffeeScript Under Pressure

I’m the primary developer on the HTML/front-end components (but not the Flash) of the Camry Effect website. It’s both the largest amount of client-side code I’ve written for a project, and the first project I’ve done with CoffeeScript. It was also a fairly high-pressure project for many different reasons.

This post will describe the project, and detail my experiences developing it in CoffeeScript.


We were brought into the project six weeks before delivery. What had been planned as a pure-Flash site suddenly needed to work on mobile (particularly iPad), so we were called in to build it in HTML.

It wasn’t just fancy HTML we had to build; it was a port of a graphic- and animation-intensive Flash app, with the polish intact,1 and it had to work on iOS. It had to work on IE7. It had to work on Android 2.1 on one of the clients’ phones. And we had six weeks. We did the maths and figured that at twelve hours a day, six days a week for six weeks, we might just sneak in.

As if that wasn’t tricky enough, we had no control over the backend. There was a JSON datastore that had been built for the site, but our deliverable had to be purely static — everything would have to run client-side, and as much as possible from a CDN.

There were also three levels of stakeholders above us, with different priorities, and constantly shifting (and always growing) specs cascading down from above as the site took shape.

After some discussion with my ‘if I get hit by a truck’ backup developer, I decided to add CoffeeScript to this, despite no real experience with it. It promised decent gains, and looked like not too much to learn.


Six months later, we’re still working on this website. It now consists of more than six thousand lines of CoffeeScript, two thousand of Javascript (source, not CoffeeScript output), another twelve hundred lines of HTML templates and snippets, and four thousand lines of LESS CSS to style it all.

The originally-specced 3.5 page site has blown out to twice that (if you can count a fifteen-state state machine or a dynamic 3D scene as single pages), with significantly richer functionality on every page, and there is a separate-but-concurrent Spanish version of the site, which we also maintain.2 Just about every page refers to or includes modules originally built for other pages. We had no idea how big and tangled this site was going to get.

You may have seen it advertised during the 2012 Super Bowl.

Why CoffeeScript?

I’d heard good things about CoffeeScript, and it definitely looked more succinct and less error-prone than Javascript. This appealed to me as I looked down the barrel of a terrifying amount of work.

Also, I’m no Javascript expert, and I’m not terribly confident with it3 either in the large (modules, structure, big-picture stuff), or in the corners, where browser quirks and language warts live. CoffeeScript seemed cleaner and more modern than JS, and it looked like it might do for JS much what jQuery does for cross-browser issues, papering over the most annoying mismatches.

The site as specified at the beginning of the project didn’t look broad enough to be worth investing in a full framework or library, and I didn’t think I’d have time to learn anything too large. Coffee looked (at a glance, and after a quick proof-of-concept skeleton) like a good fit for the project.

I think I was hoping that CoffeeScript would have some opinions, too, about project structure, modules, whatever, but it didn’t.


CoffeeScript is a language, but it’s also a tool. Unfortunately, sometimes it’s a broken tool. In particular, for much of this project’s duration, coffee has had a nasty bug in its --watch mode which causes it to lose track (and therefore stop automatically recompiling) every time the git branch is changed. (This problem may have been fixed now.)

Restarting the watcher process is trivial enough, but remembering to restart it usually only happens after an ever-increasing series of changes to my .coffee sources which fail to have any effect at all. It’s a pretty frustrating bug.

Another unexpected problem cropped up when a second developer joined the project partway through, and installed the available version of CoffeeScript — a later one than I’d been using, with a different output format. Due to our deployment requiring the generated Javascript to be checked into the repository, this made for incredibly noisy diffs. The whole generated JS folder would complete change with each developer’s builds, until I finally upgraded my coffee install to match output styles.

-  if ((_ref = this.actions) != null) {
-    _ref;
-  } else {
-    this.actions = {};
-  };
+  if ((_ref = this.actions) == null) this.actions = {};

Our repo is full of this kind of thing. Makes code reviews annoying.

This latest point is perhaps less a complaint about CoffeeScript, and more a warning about versioning and standardising all components of a project.

Coffee in the Project

This project is a completely static deploy at my end. My Makefile concatenates, minifies and copies everything necessary into a subfolder, which is merged with other components elsewhere before being deployed to the server. An automated deployment (which is outside my control) takes forty minutes, which makes it fairly crucial to get things right — hotfixes on the server aren’t really an option.

CoffeeScript was a godsend here, simply as an explicit compile and validation step. Having to compile everything from CoffeeScript to Javascript means that it isn’t possible to deploy malformed Javascript — a git commit hook refuses to commit without a clean make.

Of course, I still managed to deploy plenty of bugs, but not a single syntax error or missing-semicolon problem got through Coffee. The fact that CoffeeScript produced not just syntactically correct but also more robust Javascript than I would have written myself was a huge additional bonus.

The language itself

CoffeeScript as a language is… slightly underwhelming, actually. A few really nice features and shortcuts (function (x) {}  just doesn’t compare to the (x) ->  lambda syntax) just don’t quite manage to outweigh the quirks of the indentation rules and the feeling that there’s three ways to do everything. I really like for x in xs. I don’t really use the list comprehensions (which Andrew Brehaut had some things to say about), because I tend to use map and filter anyway.

This is at least an order of magnitude more client-side code than I’ve ever written for a project. I was a bit surprised to discover that CoffeeScript has no more opinions on code structure than does Javascript (short a class syntax which I barely used.) Presumably it plays perfectly well with JS dependency-management systems and the like; I never tried.4

In hindsight, I would have been better served learning a suitable framework/library for this project than a new language. CoffeeScript is just a less-typing way to do exactly what I’ve always done in the browser, which in this case has turned out to be six thousand lines of semi-modular code with a tendency towards spaghetti.

Less typing seems like a good idea (and it may have saved my butt given the early schedule of this site — a two month sprint), but I feel like maybe it just allowed me to type first, think later. I really wish I had spent a bit of time and put some serious thinking and planning into this site before I started typing.

Less typing is also in many places just a compensation for a lacking standard library. (This is a Javascript criticism.) The lack of a strong set of standard control and data structures means that you end up typing many of the same patterns repeatedly — arguably, more efficient expression of these patterns is the wrong solution to this problem.

None of this is to say that CoffeeScript isn’t helpful. There are a number of features that are all too easy to forget about, but that I’m sure have a huge effect on code quality. Automatic local scoping (no var necessary) is a sane choice, and safe loop scoping with for x in y do (x) ->  erases a whole category of errors. Implicit returns are nothing short of fantastic. Easy lambdas do encourage more functional programming (which suits me well), and indentation and the lack of noisy punctuation make code read more easily. I definitely miss these back in Javascript.

On the whole, though, I don’t think CoffeeScript adds quite enough benefit to outweigh the costs, and many of the benefits I get from it could be duplicated by a good choice of framework. It has some annoying quirks, too, that just add friction. I had a lot of trouble with the indentation rules in certain cases; for instance:

    # (note weird hanging comma & time argument)
    setTimeout ->
    , 5000

I’ve had more trouble with CoffeeScript’s indentation rules than I ever had with Python or Haskell, and that’s also true for other people I’ve talked to.

I’ll miss many of Coffee’s niceties, but it just doesn’t feel quite robust enough (as a language or as a tool) that I’m confident in it at this sort of scale, and at smaller scales it doesn’t confer enough benefit to be worth the added complexity. Your mileage may of course vary. It is still possible that I may find a return to plain Javascript sufficiently painful that I’ll stick with Coffee.


Next time I do something at this scale, I’ll start with dependency management, maybe use Google Closure for an explicit compilation/validation step (on top of "use strict";), and probably take some lessons from Addy Osmani’s article which I unfortunately only discovered well into this project.

My biggest mistake was probably the assumption that the project would remain as specified. Projects always grow in scope. It was always going to be more complicated than it seemed up front.

After all of that, though, the final product is a site that works as required, and that’s got to be considered a success.

Discussion at Hacker News and the Javascript Reddit.

  1. For example, the designers would send me Flash animations of particular transitions, with screenshots of the easings and timings all marked up for me to exactly duplicate.

  2. It was a late-breaking requirement, and is maintained as a fork. It has diverged significantly from the English version, and is a pretty good example of the wrong way to build multi-language sites.

  3. Our sites are usually more traditional page-based, server-driven things, more Django than jQuery. A bit of AJAX, sure. A full JS app, not so much.

  4. The CoffeeScript is broken up into around 25 .coffee files, each containing a top-level namespace with all that module’s exports, as per normal practice. That’s about as much structure as there is.

07 Feb 2012