I’ve always wanted to try CoffeeScript ever since I saw it on Railscast. I finally got my chance. Luckily it comes built-in for Rails 3, but I didn’t know how it worked. At first I thought I needed to compile and downloaded the coffee compiler. It turned out to be useful to have. Rails does not give good error messages if there is a problem in the coffee script, so I run it through the compiler and it’ll give me a better idea of what’s going on.

Installing CoffeeScript. CoffeeScript is a Node.js module. Node.js is a javascript interpreter you can use outside of the browser. To install using Homebrew use

$ brew install node
$ sudo npm install -g coffee-script

and put this in your ~/.bashrc file


You can use the coffee command to compile your coffeescript.

Don’t neeed guard. I installed guard-coffeescript but I found I didn’t need it. You don’t need to compile it because Rails will automatically do it for you using the asset pipeline.

The language. Coffeescript is somewhat like python in that indents matter. if then does not need an end. You don’t need curly braces or semicolons. Sometimes you don’t need parentheses. Functions are defined using ->. So far these are simple translations that make your code smaller. You get power when you find out about the for loop. If you go to the coffeescript website, they have a really great overview of the language with lots of examples. You can even use the coffeescript interpreter directly from the browser. I found that useful when I’m developing some tricky coffeescript. You can immediately see any errors as you type then.

It’s a bit frustrating when you make some modifications to your code and it either just doesn’t work or you get an incomprehensible error. You end up looking at the resulting javascript for clues. The trouble is worth it because some of the powers of the for loop and parameter handling (you can have default args).

All in all, it’s worth looking into. Probably the best way to use it is by converting an existing javascript code and cleaning it up.

Edited 2017-01-05: Here’s an interesting resource that has some more info on coffeescript