| CoffeeScript | |
|---|---|
 | |
| Paradigms | Multi-paradigm:prototype-based,functional,imperative,scripting |
| Family | ECMAScript |
| Designed by | Jeremy Ashkenas |
| Developer | same |
| First appeared | December 13, 2009; 16 years ago (2009-12-13) |
| Stable release | |
| Typing discipline | dynamic,implicit |
| Scope | lexical |
| Implementation language | CoffeeScript |
| Platform | x86-64 |
| OS | Cross-platform |
| License | MIT |
| Filename extensions | .coffee,.litcoffee[citation needed] |
| Website | coffeescript |
| Influenced by | |
| Haskell,JavaScript,Perl,[citation needed]Python,[2]Ruby,YAML[3] | |
| Influenced | |
| MoonScript,LiveScript, JavaScript | |
CoffeeScript is aprogramming language that compiles toJavaScript. It addssyntactic sugar inspired byRuby,Python, andHaskell in an effort to enhance JavaScript's brevity and readability.[4][5] Some added features includelist comprehension anddestructuring assignment.
CoffeeScript support is included inRuby on Rails version 3.1[6] andPlay Framework.[7] In 2011,Brendan Eich referenced CoffeeScript as an influence on his thoughts about the future of JavaScript.[8][9]
On December 13, 2009,Jeremy Ashkenas made the firstGit commit of CoffeeScript with the comment "initial commit of the mystery language".[10] 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 aself-hosting version in pure CoffeeScript. By that time the project had attracted several other contributors onGitHub, and was receiving over 300 page hits per day.
On December 24, 2010, Ashkenas announced the release of stable 1.0.0 toHacker News, the site where the project was announced for the first time.[11][12]
On September 18, 2017, version 2.0.0 was introduced,[13] 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".
Almost everything is anexpression in CoffeeScript, for example,if,switch andfor expressions (which have no return value in JavaScript) return a value. As inPerl and Ruby, these control statements also have postfix versions; for example,if can also be written in consequent if condition form.
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.
To compute thebody mass index inJavaScript, one could write:
letmass=72;letheight=1.78;letBMI=mass/height**2;if(18.5<=BMI&&BMI<25)alert('You are healthy!');
With CoffeeScript the interval is directly described:
mass=72height=1.78BMI=mass/height**2alert'You are healthy!'if18.5<=BMI<25
To compute thegreatest common divisor of two integers with theEuclidean algorithm, in JavaScript one usually needs awhile loop:
letgcd=(x,y)=>{do{[x,y]=[y,x%y];}while(y!==0)returnx;}
Whereas in CoffeeScript one can useuntil[14] instead:
gcd=(x, y) ->[x,y]=[y,x%y]untilyis0x
The? keyword quickly checks if a variable isnull orundefined :
personCheck=->ifnotperson?thenalert("No person")elsealert("Have person")person=nullpersonCheck()person="Ivan"personCheck()
This would alert "No person" if the variable isnull orundefined and "Have person" if there is something there.
A common pre-ES6 JavaScript snippet using thejQuery library is:
$(document).ready(function(){// Initialization code goes here});
Or even just:
$(function(){// Initialization code goes here});
In CoffeeScript, thefunction keyword is replaced by the-> symbol, and indentation is used instead of curly braces, as in otheroff-side rule languages such as Python and Haskell. Also, parentheses can usually be omitted, using indentation level instead to denote a function or block. Thus, the CoffeeScript equivalent of the snippet above is:
$(document).ready-># Initialization code goes here
Or just:
$-># Initialization code goes here
Ruby-style string interpolation is included in CoffeeScript. Double-quoted strings allow for interpolated values, using #{ ... }, and single-quoted strings are literal.[15]
author="Wittgenstein"quote="A picture is a fact. --#{author}"sentence="#{22/7} is a decent approximation of π"
Anyfor loop can be replaced by alist comprehension; so that to compute the squares of the positive odd numbers smaller than ten (i.e. numbers whose remainder modulo 2 is 1), one can do:
alertn*nfornin[1..10]whenn%2is1
Alternatively, there is:
alertn*nfornin[1..10]by2
Alinear search can be implemented with a one-liner using the when keyword:
names=["Ivan","Joanna","Nikolay","Mihaela"]linearSearch=(searchName) ->alert(name)fornameinnameswhennameissearchName
Thefor ... in syntax allows looping over arrays while thefor ... of syntax allows looping over objects.
CoffeeScript has been criticized for its unusualscoping rules.[16][17] In particular, it completely disallowsvariable shadowing which makes reasoning about code more difficult and error-prone in some basic programming patterns establishedby and taken for granted sinceprocedural programming principles were defined.
For example, with the following code snippet in JavaScriptone does not have to look outside the{}-block to know forsure that no possiblefoo variable in the outer scope can beincidentally overridden:
// ...functionbaz(){varfoo="bar";console.log(`foo =${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.
The CoffeeScript compiler has beenself-hosting since version 0.5 and is available as aNode.js utility; however, the core compiler does not rely on Node.js and can be run in anyJavaScript environment.[18] One alternative to theNode.js utility is the Coffee Maven Plugin, a plugin for theApache Maven build system. The plugin uses theRhino JavaScript engine written inJava.[citation needed]
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[19] site provides bi-directional translation.
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.coffee.md or.litcoffee file extension. This allows thesource code to be written inMarkdown. The compiler will treat any indented blocks (Markdown's way of indicating source code) as code, and ignore the rest as comments.Iced CoffeeScript is a superset of CoffeeScript which adds two new keywords:await anddefer. These additions simplify asynchronous control flow, making the code look more like aprocedural programming language, eliminating the call-back chain. It can be used on the server side and in the browser.[20]
On September 13, 2012,Dropbox announced that their browser-side code base had been rewritten fromJavaScript to CoffeeScript,[21] however it was migrated toTypeScript in 2017.[22]
GitHub's internal style guide once said "write new JS in CoffeeScript", though it no longer does,[23] and itsAtom text editor was also written in the language, with configuration written inCSON ("CoffeeScript Object Notation"), a variant ofJSON.[24][25]
Pixel Game Maker MV makes uses of CoffeeScript as part of its game development environment.[26]
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