Making is thinking.


The syntax of CoffeeScript, a programming language that transpiles to JavaScript, is elegant; but transpilers, although influential to future development of languages, are traditionally not well received.

I TREASURE JAVASCRIPT for its flexibility. Even though its syntax isn’t great, and it definitely has its quirks—which I tolerate like those of an old companion—I enjoy JavaScript programming. That said, I’ve been intrigued by CoffeeScript since its introduction, and its appeal increased further, when I heard that Ward Cunningham uses it in his new wiki. This quiet site offered a welcomed opportunity to finally try CoffeeScript.

JavaScript is a lightweight, object-oriented language, mostly known as the scripting language for web pages, but used in many non-browser environments as well. JavaScript was created in 1995 by Brendan Eich at Netscape. His objective was to make it look like Java, but subversively he made it look like C. The name was a marketing stunt to free ride the Java hype of the time. The language however has nothing in common with Java, its idiotic name has been contributing to JavaScript’s misinterpretation until recently. JavaScript is the Cinderella of programming languages, long time abused and underrated until its foot fit the golden slipper—from battered toy to lingua franca of the web. Today JavaScript is the top language on GitHub.

Popular JavaScript engines are: V8, JavaScriptCore, and SpiderMonkey.

CoffeeScript is a programming language written by Jeremy Ashkenas. Its syntax is inspired by Ruby, Python, and Haskell; it adds features like comprehensions and pattern matching. The self hosted source-to-source compiler (written in CoffeeScript) uses the jison JavaScript parser generator to translate CoffeeScript to JavaScript.

Jeremy Ashkenas, distinguished through backbone and underscore, began the CoffeeScript experiment in 2010 to answer a simple question:

What would JavaScript look like, if it could like anything you wanted it to look like?

Selected CoffeeScript Features

Splats and Default Arguments
{ test } = require('tap')
add = (sum, values...) ->
  sum += value for value in values
test 'add'(t) ->
  t.equal add(123)6'should be 6'
say = (what = 'Hello') ->
test 'say'(t) ->
  t.equal say()'Hello''should be Hello'
  t.equal say('Ciao')'Ciao''should be Ciao'
String Interpolations
{ test } = require 'tap'
name = 'Coltrane'
test 'string'(t) ->
  t.equal "John #{ name }"'John Coltrane''should be John Coltrane'
  t.equal "1 + 2 = #{ 1 + 2 }"'1 + 2 = 3''should be 1 + 2 = 3'
Destructuring Assignments
{ test } = require('tap')
{ name } = name: 'Moe'
test 'assignment'(t) ->
  t.equal name'Moe''should be Moe'
Array Comprehensions
{ test } = require('tap')
getItem = (name) ->
  name: name
moe = getItem 'Moe'
larry = getItem 'Larry'
curly = getItem 'Curly'
items = [moelarrycurly]
test 'iterate'(t) ->
  = 0
  (i++) for item in items
  t.equal i3'should be 3'
test 'map'(t) ->
  names = ( for item in items)
  t.equal typeof name'string''should be string' for name in names
  t.equal names.length3'should be 3'
test 'filter'(t) ->
  item = (item for item in items when is 'Curly')[0]
  t.same itemcurly'should be curly'
Classes and Inheritance
{ test } = require 'tap'
class Animal
  constructor: (@name) ->
class Dog extends Animal
  greet: () ->
class Beagle extends Dog
  greet: () ->
    super + ' Woof!'
test 'dogs'(t) ->
  cheech = new Dog 'Cheech'
  t.equal'Cheech''should be Cheech'
  t.equal cheech.greet()'Woof!''should be Woof!'
  chong = new Beagle 'Chong'
  t.equal'Chong''should be Chong'
  t.equal chong.greet()'Woof! Woof!''should be Woof! Woof!'

But details aside, the three most significant features of CoffeeScript are: meaningful whitespace, implicit function returns, and less code. Meaningful whitespace prevents boring discussions about code formatting (semicolons anyone?), implicit function returns cultivate functional programming style, and less code is less code.

How about debugging? As one of CoffeeScript’s design principles is to maintain the order of instructions in the compiled JavaScript code, it’s fairly easy to relate JavaScript stack traces back to CoffeeScript code. I had expected it to be much harder; debugging hasn’t been an issue for me so far. But although the generated code is readable, and potentially inspiring for some, one cannot deny the additional layer of complexity caused by the extra step of translation.

Since 3.1 Rails ships with CoffeeScript—introducing it at RailsConf 2011 DHH stated:

Looking at CoffeeScript was the first time I got a little bit of language envy.

Dreaming about JavaScript Harmony Brendan Eich wrote:


There has been an amusing discourse about CoffeeScript’s usefulness in the Node community. Most protagonists wrinkle their nose, but Mikeal Rogers downright loves CoffeeScript.

Isaac Schlueter is right:

CoffeeScript does not offer an order of magnitude difference in expressiveness. I’m not using “expressiveness” as some fuzzy term to mean “how happy you are expressing yourself in X language”, but the more mathy technical meaning of “how many relevant program tokens are required to do X task.” CoffeeScript may require fewer tokens, sure, but not 10 to 1 fewer.

Transpilers are inherently divisive. People who are fluent in the target language will hate the new language; people new to the target language will love the new language, especially if it’s related to a language they already know.

Most transpilers are valuable. Not only can they inspire further progress, but they also draw new people to their respective target language. CoffeeScript pulls Ruby programmers on board of the Black Pearl.

It’s just JavaScript. CoffeeScript waives instruction reordering to stay close to JavaScript. Evidently too close for Max Krohn, he forked CoffeeScript to write IcedCoffeeScript, which adds synchronous control flow mimicry by introducing two new keywords: await and defer. Coco is another more radical CoffeeScript dialect. The CoffeeScript wiki provides an extensive list of languages that transpile to JavaScript.

Unrelated to CoffeeScript, but nevertheless interesting: Six, a transpiler that enables new syntactic features from ECMAScript 6 today.

Any new language pushes the envelope (even by just fueling conversations), and any new language you learn makes you a better programmer. But quite frankly, despite this glamorous variety, I prefer to write vanilla JavaScript—as implemented by V8 which is ECMA-262, 5th edition. The reason for this is that I mainly write Node modules. Node is about small open source modules written by the community. Writing Node modules in CoffeeScript artificially limits the number of users and contributors; it corrodes transparency, and makes the code base harder to manage. At LXJS Owen Barnes mentioned plans to rewrite his popular Socket Stream framework in JavaScript.

Ĉu vi parolas Esperanton? Donald Knuth neither:


JavaScript is the English of the web: we use it because we use it.

You see that my objections are merely based on practical concerns; I enjoy the elegance of CoffeeScript, and find it delightful that Michael Ficarra secured funding to make a better compiler. Programming languages need independent influence from outside committees and corporations. We should be open to all language developments by independent parties.