CoffeeScript Major Mode

An Emacs major mode for CoffeeScript, unfancy JavaScript.

Provides syntax highlighting, indentation support, imenu support, a menu bar, and a few cute commands.

Installation

In your shell:

$ cd ~/.emacs.d/vendor
$ git clone git://github.com/defunkt/coffee-mode.git

In your emacs config:

(add-to-list 'load-path "~/.emacs.d/vendor/coffee-mode")
(require 'coffee-mode)

If coffee-mode is not enabled automatically for any files ending in ".coffee" or named "Cakefile", add this to your emacs config as well:

(add-to-list 'auto-mode-alist '("\\.coffee$" . coffee-mode))
(add-to-list 'auto-mode-alist '("Cakefile" . coffee-mode))

Indentation

Configuring

Lines are indented according to the tab-width variable. If you're like me, you probably have this set in your Emacs config globally:

(setq-default tab-width 4)

Well, idiomatic CoffeeScript uses two spaces. We can set our tab-width to two for coffee-mode using the coffee-mode-hook:

(defun coffee-custom ()
  "coffee-mode-hook"
 (set (make-local-variable 'tab-width) 2))

(add-hook 'coffee-mode-hook
  '(lambda() (coffee-custom)))

For more configuration options and another example of this hook, look further down in this README.

TAB Theory

It goes like this: when you press TAB, we indent the line unless doing so would make the current line more than two indentation levels deepers than the previous line. If that's the case, remove all indentation.

Consider this code, with point at the position indicated by the caret:

line1()
  line2()
  line3()
     ^

Pressing TAB will produce the following code:

line1()
  line2()
    line3()
       ^

Pressing TAB again will produce this code:

line1()
  line2()
line3()
   ^

And so on. I think this is a pretty good way of getting decent indentation with a whitespace-sensitive language.

Newline and Indent

We all love hitting RET and having the next line indented properly. Given this code and cursor position:

line1()
  line2()
  line3()
        ^

Pressing RET would insert a newline and place our cursor at the following position:

line1()
  line2()
  line3()

  ^

In other words, the level of indentation is maintained. This applies to comments as well. Combined with the TAB you should be able to get things where you want them pretty easily.

Indenters

class, for, if, and possibly other keywords cause the next line to be indented a level deeper automatically.

For example, given this code and cursor position::

class Animal
            ^

Pressing enter would produce the following:

class Animal

  ^

That is, indented a column deeper.

This also applies to lines ending in ->, =>, {, [, and possibly more characters.

So this code and cursor position:

$('#demo').click ->
                   ^

On enter would produce this:

$('#demo').click ->

  ^

Pretty slick.

imenu

If you're using imenu, coffee-mode should work just fine. This means users of textmate.el will find that ⇧⌘T (textmate-go-to-symbol) mostly works as expected.

If you're not using imenu check out this page or textmate.el for a really awesome way to jump quickly to a function's definition in a file.

Commands

If you have easymenu you can get to any of these commands from the menu bar:

coffee-compile-file

Compiles the current file as a JavaScript file. Doesn't open it or anything special for you.

Operating on "basic.coffee" and running this command will save a "basic.js" in the same directory. Subsequent runs will overwrite the file.

If there are compilation errors and we the compiler have returned a line number to us for the first error, the point is moved to that line, so you can investigate. If this annoys you, you can set coffee-compile-jump-to-error to nil.

coffee-compile-buffer

Compiles the current buffer to JavaScript using the command specified by the coffee-command variable and opens the contents in a new buffer using your JavaScript mode of choice. The JavaScript mode is determined by the coffee-js-mode variable and defaults to js2-mode.

Bind it:

(define-key coffee-mode-map [(meta r)] 'coffee-compile-buffer)

coffee-compile-region

Compiles the selected region to JavaScript using the same configuration variables as coffee-compile-buffer.

Bind it:

(define-key coffee-mode-map [(meta R)] 'coffee-compile-region)

Compile-on-save

Hitting the key sequence C-c C-o C-s turns on (toggles) the compile-on-save minor mode in coffee-mode. To enable it by default:

(add-hook 'coffee-mode-hook '(lambda () (coffee-cos-mode t)))

To enable it only if it looks like you may want to:

(add-hook 'coffee-mode-hook '(lambda ()
                               (and (file-exists-p (buffer-file-name))
                                    (file-exists-p (coffee-compiled-file-name))
                                    (coffee-cos-mode t))))

coffee-repl

Starts a repl in a new buffer using coffee-command.

Hooks

coffee-mode-hook

Naturally. Example:

(defun coffee-custom ()
  "coffee-mode-hook"

  ;; CoffeeScript uses two spaces.
  (set (make-local-variable 'tab-width) 2)

  ;; If you don't have js2-mode
  (setq coffee-js-mode 'javascript-mode)

  ;; If you don't want your compiled files to be wrapped
  (setq coffee-args-compile '("-c" "--bare"))

  ;; *Messages* spam
  (setq coffee-debug-mode t)

  ;; Emacs key binding
  (define-key coffee-mode-map [(meta r)] 'coffee-compile-buffer)

  ;; Riding edge.
  (setq coffee-command "~/dev/coffee"))

  ;; Compile '.coffee' files on every save
  (and (file-exists-p (buffer-file-name))
       (file-exists-p (coffee-compiled-file-name))
       (coffee-cos-mode t))))

(add-hook 'coffee-mode-hook 'coffee-custom))

Configuration

You can customize any of the following options using M-x customize-group with "coffee" as the group.

You can also customize then with coffee-mode-hook, as demonstrated above.

coffee-debug-mode

Whether to run in debug mode or not. Logs to *Messages*.

Default: t

coffee-js-mode

The mode to use when viewing compiled JavaScript.

Default: 'js2-mode

coffee-cleanup-whitespace

Should we `delete-trailing-whitespace' on save? Probably.

Default: t

coffee-tab-width

The tab width to use when indenting.

Default: tab-width

coffee-command

The CoffeeScript command used for evaluating code. Must be in your path.

Default: "coffee"

coffee-args-repl

The command line arguments to pass to `coffee-command' to start a REPL.

Default: '("-i")

coffee-args-compile

The command line arguments to pass to `coffee-command' when compiling a file.

Default: '("-c")

coffee-compiled-buffer-name

The name of the scratch buffer used when compiling CoffeeScript.

Default: "*coffee-compiled*"

coffee-compile-jump-to-error

Whether to jump to the first error if compilation fails. Please note that the coffee compiler doesn't always give a line number for the issue and in that case it is not possible to jump to the error, of course.

Default: t

Thanks

• Jeremy Ashkenas for CoffeeScript
• http://xahlee.org/emacs/elisp_syntax_coloring.html for instructions.
• Jason Blevins for the guidance his markdown-mode.el gave.
• Steve Yegge for js2

Bugs

Prototype accessor assignments like String::length: -> 10 don't look great.

It's tested on Aquamacs 1.9 (Emacs 22) for OS X Snow Leopard so it may not work on your environment. Please file a bug at http://github.com/defunkt/coffee-mode/issues and maybe we can fix the problem.

This is the author's first major mode, so there are probably more bugs.