CoffeeScript

CoffeeScript

Paradigm	Multi-paradigm: prototype-based, functional, imperative, scripting
Designed by	Jeremy Ashkenas
Developer	Jeremy Ashkenas
First appeared	December 13, 2009 (2009-12-13)
Stable release	2.3.2 / September 20, 2018 (2018-09-20)[1]
OS	Cross-platform
License	MIT License
Filename extensions	.coffee, .litcoffee
Website	coffeescript.org
Influenced by
Haskell, JavaScript, Perl, Python,[2] Ruby, YAML[3]
Influenced
MoonScript, LiveScript, JavaScript

CoffeeScript is a programming language that transcompiles to JavaScript. It adds syntactic sugar inspired by Ruby, Python and Haskell in an effort to enhance JavaScript's brevity and readability.^[4] Specific additional features include list comprehension and pattern matching.

CoffeeScript support is included in Ruby on Rails version 3.1^[5] and Play Framework.^[6] In 2011, Brendan Eich referenced CoffeeScript as an influence on his thoughts about the future of JavaScript.^[7][8]

History

On December 13, 2009, Jeremy Ashkenas made the first Git commit of CoffeeScript with the comment: "initial commit of the mystery language."^[9] The compiler was written in Ruby. On December 24, he made the first tagged and documented release, 0.1.0. On February 21, 2010, he committed version 0.5, which replaced the Ruby compiler with a self-hosting version in pure CoffeeScript. By that time the project had attracted several other contributors on GitHub, and was receiving over 300 page hits per day.

On December 24, 2010, Ashkenas announced the release of stable 1.0.0 to Hacker News, the site where the project was announced for the first time.^[10][11]

On September 18, 2017, version 2.0.0 was introduced^[12], which "aims to bring CoffeeScript into the modern JavaScript era, closing gaps in compatibility with JavaScript while preserving the clean syntax that is CoffeeScript’s hallmark."

Syntax

Almost everything is an expression in CoffeeScript, for example if, switch and for expressions (which have no return value in JavaScript) return a value. As in Perl, these control statements also have postfix versions; for example, if can also be written after the conditional statement.

Many unnecessary parentheses and braces can be omitted; for example, blocks of code can be denoted by indentation instead of braces, function calls are implicit, and object literals are often detected automatically.

Examples

var mass = 72;
var height = 1.78;
var BMI = mass / Math.pow(height, 2);
if (18.5 < BMI && BMI < 25) alert('You are healthy!');

mass = 72
height = 1.78
BMI = mass / height**2
alert 'You are healthy!' if 18.5 < BMI < 25

gcd = (x, y) => {
  do {
    z = x % y
    x = y
    y = z
  } while (y !== 0)
  return x
}

gcd = (x, y) ->
  [x, y] = [y, x%y] until y is 0
  x

alert n*n for n in [1..10] when n%2 is 1

alert n*n for n in [1..10] by 2

names = ["Ivan", "Joanna", "Nikolay", "Mihaela"]
linearSearch = (searchName) -> alert(name) for name in names when name is searchName

personCheck = ->
  if not person? then alert("No person") else alert("Have person")
person = null
personCheck()
person = "Ivan"
personCheck()

$(document).ready(function() {
  // Initialization code goes here
})

$(function() {
  // Initialization code goes here
})

$(document).ready ->
  # Initialization code goes here

$ ->
  # Initialization code goes here

author = "Wittgenstein"
quote  = "A picture is a fact. -- #{ author }"

sentence = "#{ 22 / 7 } is a decent approximation of π"

Compiling

The CoffeeScript compiler has been written in CoffeeScript since version 0.5 and is available as a Node.js utility; however, the core compiler does not rely on Node.js and can be run in any JavaScript environment.^[14] One alternative to the Node.js utility is the Coffee Maven Plugin, a plugin for the popular Apache Maven build system. The plugin uses the Rhino JavaScript engine written in Java.

The official site at CoffeeScript.org has a "Try CoffeeScript" button in the menu bar; clicking it opens a modal window in which users can enter CoffeeScript, see the JavaScript output, and run it directly in the browser. The js2coffee^[15] site provides bi-directional translation.

Latest additions

• Source maps allow users to de-bug their CoffeeScript code directly, supporting CoffeeScript tracebacks on run time errors.
• CoffeeScript supports a form of Literate Programming, using the .coffee.md or .litcoffee file extension. This allows CoffeeScript source code to be written in Markdown. The compiler will treat any indented blocks (Markdown's way of indicating source code) as code, and ignore the rest as comments.

Adoption

On September 13, 2012, Dropbox announced that their browser-side code base has been rewritten from JavaScript to CoffeeScript.^[16]

GitHub's internal style guide once said "write new JS in CoffeeScript", and while it no longer does, all the advice in the style guide references how to write good CoffeeScript,^[17] and their Atom text editor is also written in the language.^[18]

Criticism

CoffeeScript has been criticized for it's unusual scoping rules^[19][20]. In particular, it completely disallows variable shadowing which makes reasoning about code more difficult and error-prone in some basic programming patterns established by and taken for granted since procedural programming principles were defined.

For example with the following code snipped in JavaScript one does not have to look outside the {}-block to know for sure that no possible foo variable in the outer scope can be incidentally overriden:

  // ...
  {
    var foo = "bar";
    console.log(`foo = ${foo}`)
  }
  // ...
}

In CoffeeScript there is no way to tell if the scope of a variable is limited to a block or not without looking outside the block.

See also

• Source-to-source compiler

References

Further reading

• Lee, Patrick (May 14, 2014). "CoffeeScript in Action" (First ed.). Manning Publications: 432. ISBN 978-1617290626.
• Grosenbach, Geoffrey (May 12, 2011). "Meet CoffeeScript" (First ed.). PeepCode.
• Bates, Mark (May 31, 2012). "Programming in CoffeeScript" (First ed.). Addison-Wesley: 350. ISBN 0-321-82010-X.
• MacCaw, Alex (January 31, 2012). "The Little Book on CoffeeScript" (First ed.). O'Reilly Media: 62. ISBN 978-1449321055.
• Burnham, Trevor (August 3, 2011). "CoffeeScript: Accelerated JavaScript Development" (First ed.). Pragmatic Bookshelf: 138. ISBN 978-1934356784.

External links

• Official website