> 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.
    > [...]
    > 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.

I think it goes without saying that "on deadline" is probably not the best time to learn a brand new JavaScript dialect. I'm relieved to hear that it all turned out for the best.

You mention that you're thinking of adding an explicit validation step -- great idea. For CS & JS (which can be compiled and validated quickly), even better than having it run when you build is having it run every time you save the file in your text editor...

This article gives a perfect example of why you would want to take advantage of the git index: the author was talking about different versions of coffee sometimes producing different output which lead to commits going back and forth between the two versions.

The author is right: this is annoying.

Now, the correct way to solve this would probably be to either not check in generated files, to leave the JS out of the repo, or, if that's not possible due to politics, then use the same version of coffee which I would highly recommend anyways because it gets rid of really bad WTFy issues if one version of the compiler has a bug which manifests itself in an application bug which will then only be seen if the last commit was done by the person with the broken compiler.

Anyways. Let's say you can't use the same compiler and you have to check in JS in addition to coffee (you are not trying to sneak in coffee by ONLY committing the JS, are you?)

Now we have the perfect oportunity to show off the git index:

Instead of committing the whole file, you would use add -p to only select the changes which are actual code changes and not changes in compiler output.

Then you would only commit those changes and then undo the unneeded stuff and test again, to ensure that you added the right lines to the index (commit --amend or rebase -i if not).

This will give you a much cleaner history, which will be a huge help when blaming or reviewing the code. No more annoying flip-flopping between compiler output styles. No more meaningless changes in a commit. All the changed lines in the diff are the lines that count. The lines you should look at when reviewing. No risk of missing the trees in the forest.

But, you might say, history rewriting is bad. I don't want to commit something I haven't tested.

Remember though: you haven't pushed yet. You haven't altered public history yet. Nobody knows about those commits yet. You have all the time for testing, patching and massaging commits. Only once you pushed, your changes (should) become set in stone. Only then, history gets written. Only then it can't be changed any more.

This is why I love rebase and I'm really glad I finally found a good real-world example to show why.

Aside from being a good read, the author comes off as the kind of person I would like to work with.

For what it's worth, facing a client-side project of similar magnitude, we chose Google Web Toolkit and learned Java.

Two years and 60k LOC later, (www.activityinfo.org) I'm not entirely satisfied with the tool -- sometimes more abstraction introduces new problems to be solved, and it's hard to find good, affordable java devs to work on the project here in NL, but it does IMHO bring tremendous advantages in terms of modularity, dependency management, and generally keeping the code base maintainable. And the optimizing compiler is nothing short of amazing.

I realize the idea of Java-to-Javascript is sacrilege for many, but if you've looking at building a large, single-page javascript application, I think it's worth taking a look at.

We recently have switched over to using CoffeeScript in production and haven't looked back. One thing we found out real fast was to not compile the CS until you go to staging or QA. The way we get around this is using RequireJS (http://requirejs.org/) and the CoffeeScript Plugin(https://github.com/jrburke/require-cs). This buys you the ability to compile at runtime in the browser, so you don't have this mess of CoffeeScript files and compiled JS files in your source. When you are ready to build for production or QA you use RequireJS' optimization tools to concatenate, minify, obfuscate and compile the code. Hope that helps.

A very well written article.

I've considered learning CoffeeScript but have decided for now to let things play out and focus on learning JavaScript better. There are a ton of frameworks for javascript (backbone/spine) that make it more bearable. Also JS for all its quirks is ridiculously powerful.

To me maintainability is huge in a project. There needs to be a really strong reason to choose CoffeeScript over plain javascript. Catching all syntax errors seems okay but not entirely justified. I usually catch those in a staging environment on a console.

> Due to our deployment requiring the generated Javascript to be checked into the repository, this made for incredibly noisy diffs.

Add `// Generated by' to surpress JS diffs on Github.

> 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.

CoffeeScript's list comprehensions can be used for `map' and `filter' too.

> 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.)

One cannot be saved sola gratia.

Maybe I'm just feeling cynical this morning but I don't understand why the OP came to his conclusion. I read it as him making a bunch of mistakes which led him to conclude he shouldn't use CoffeeScript.

He took on a large project on short notice with a tight deadline, browser compatibility issues, and growing requirements (client is a big company after all) using a language he's "not terribly confident with". This alone is a really Bad Idea. But I'll give him the benefit of the doubt and assume he recognizes this in hindsight and felt he could handle it at the time.

Then he decides to do it in CoffeeScript, something he has never used before. It seems he had expectations that CS was much more heavy handed, providing library-like code structure and compensating for his lack of JS knowledge. Mistake #2.

He finds a bug and some other small annoyances. This is understandable. There are some things about CS that annoy me too. Every language has its problems. I suppose this alone could be enough to drive someone away from a language. Personally I find the trade offs worth it for increased productivity, but that's just my opinion.

His conclusion about CoffeeScript is that "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." Again, problems with confidence.

My suggestion? Be confident with JavaScript first, then use CoffeeScript. Not understanding the underlying language is just going to lead to problems like this.

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

For those of us not in the US - anyone have any idea what site he is talking about?

Edit: Just saw the link in a previous comment. Seems the site is: http://toyota.com/camryeffect/

I've posted this before, but it's relevant again here, as the author mentions the dangling comma issue. Discussion on preferred syntax for a parameter spanning multiple lines followed by another parameter: https://gist.github.com/1215863

You have got to be kidding.

Paraphrasing: We were under massive time constraints and by our own estimation, already barely able to meet the deadline, so we decided to add a language which compiles Javascript even though I am not that well versed in Javascript.

There are so mnay things wrong with this approach I really don't know where to begin.

> CoffeeScript was a godsend here, simply as an explicit compile and validation step. > 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. > indentation

Thought it might be useful to others seeking these advantages that passing your JS through JSHint in the build process could provide these benefits. It's not a cure-all, of course--the author cites other benefits that linting can't achieve. But if you're a like-minded developer looking for assurances along these lines in JavaScript, check out http://jshint.com and https://github.com/jshint/jshint/

A very interesting read, although from this line I couldn't quite stop thinking "there's no silver bullet":

> I decided to add CoffeeScript to this, despite no real experience with it.

> The lack of a strong set of standard control and data structures [in JavaScript] means that you end up typing many of the same patterns repeatedly

Care to elaborate? I'm not saying I don't have my own notions of what's missing in JS, but I'd like to hear your take, given your experience.

> I don’t think CoffeeScript adds quite enough benefit to outweigh the costs

Those "costs" were the cost of learning, not development/efficiency costs.

If you are already comfortable with Javascript and know coffeescript beforehand, the cost is zero and the benefits far outweigh that.

If JS/CS typing is an issue for you, you may want to take a look at CoffeeScript Contracts, a fork of CoffeeScript that implements contracts: http://disnetdev.com/contracts.coffee/

I've not used them in production yet but it looks like a very cool way to ensure code quality. The syntax of the Contracts resembles Haskell type definitions. Contracts are very flexible -- for example, you could create and enforce a "Prime Number" type (or whatever type you wish).

Also, you don't have to include the contracts in your production code -- you can compile to JS for production and omit the contracts once you've validated the code against them.

Actually, the more I look at this, the more I think I'll use it for my next CoffeeScript project.

would like to see the app. it seems like it would have been a hard task.

now, trying to think of which apps were featured during the super bowl. the GM one? anyone have any guesses?

It shouldn't matter what the generated code is. Use gitattributes to ignore diffs on generated folders.

Uhm, I don't think CoffeeScript is meant to be used on production mission critical projects. It's a research language, not a "fix javascript" language. That so many people are going ahead and using it in production anyway really raises some serious questions about how technology choices get made.