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<%
require 'uv'
def code_for(file, executable=false)
@stripper ||= /(\A\(function\(\)\{\n|\}\)\(\);\n*\Z|^ )/
return '' unless File.exists?("documentation/js/#{file}.js")
cs = File.read("documentation/coffee/#{file}.coffee")
js = File.read("documentation/js/#{file}.js").gsub(@stripper, '')
cshtml = Uv.parse(cs, 'xhtml', 'coffeescript', false, 'idle', false)
jshtml = Uv.parse(js, 'xhtml', 'javascript', false, 'idle', false)
append = executable == true ? '' : "alert(#{executable});"
run = executable == true ? 'run' : "run: #{executable}"
button = executable ? "<button onclick='javascript: #{js};#{append}'>#{run}</button>" : ''
"<div class='code'>#{cshtml}#{jshtml}#{button}<br class='clear' /></div>"
end
%>
<!DOCTYPE html>
<html>
<head>
<meta http-equiv="content-type" content="text/html;charset=UTF-8" />
<title>CoffeeScript</title>
<link rel="stylesheet" type="text/css" href="documentation/css/docs.css" />
<link rel="stylesheet" type="text/css" href="documentation/css/idle.css" />
<link rel="shortcut icon" href="documentation/images/favicon.ico" />
</head>
<body class="minimized">
<div id="fadeout"></div>
<div id="flybar">
<a id="logo" href="#top"> </a>
<div class="navigation toc">
<div class="button">
Table of Contents
</div>
<div class="contents">
<a href="#overview">Mini Overview</a>
<a href="#installation">Installation and Usage</a>
<a href="#language">Language Reference</a>
<a href="#whitespace">Significant Whitespace</a>
<a href="#functions">Functions and Invocation</a>
<a href="#assignment">Assignment</a>
<a href="#objects_and_arrays">Objects and Arrays</a>
<a href="#lexical_scope">Lexical Scoping and Variable Safety</a>
<a href="#conditionals">Conditionals, Ternaries, and Conditional Assignment</a>
<a href="#aliases">Aliases</a>
<a href="#splats">Splats...</a>
<a href="#while">While & Until Loops</a>
<a href="#comprehensions">Comprehensions (Arrays, Objects, and Ranges)</a>
<a href="#slice_splice">Array Slicing and Splicing with Ranges</a>
<a href="#expressions">Everything is an Expression</a>
<a href="#existence">The Existential Operator</a>
<a href="#classes">Classes, Inheritance, and Super</a>
<a href="#pattern_matching">Pattern Matching</a>
<a href="#fat_arrow">Function Binding</a>
<a href="#embedded">Embedded JavaScript</a>
<a href="#switch">Switch/When/Else</a>
<a href="#try">Try/Catch/Finally</a>
<a href="#comparisons">Chained Comparisons</a>
<a href="#interpolation">String and RegExp Interpolation</a>
<a href="#strings">Multiline Strings and Heredocs</a>
<a href="#cake">Cake, and Cakefiles</a>
<a href="#scripts">"text/coffeescript" Script Tags</a>
<a href="#resources">Resources</a>
<a href="#webchat">Web Chat (IRC)</a>
<a href="#change_log">Change Log</a>
</div>
</div>
<div class="navigation try">
<div class="button">
Try CoffeeScript
</div>
<div class="contents repl_wrapper">
<div class="code">
<div id="repl_source_wrap"><textarea id="repl_source">reverse: (string) ->
string.split('').reverse().join ''
alert reverse '.eeffoC yrT'</textarea></div>
<pre id="repl_results"></pre>
<button class="full_screen">go full screen</button>
<button class="minimize">minimize</button>
<button class="run">run</button>
<br class="clear" />
</div>
</div>
</div>
<div class="navigation annotated">
<div class="button">
Annotated Source
</div>
<div class="contents">
<a href="documentation/docs/grammar.html">Grammar Rules — src/grammar</a>
<a href="documentation/docs/lexer.html">Lexing Tokens — src/lexer</a>
<a href="documentation/docs/rewriter.html">The Rewriter — src/rewriter</a>
<a href="documentation/docs/nodes.html">The Syntax Tree — src/nodes</a>
<a href="documentation/docs/scope.html">Lexical Scope — src/scope</a>
<a href="documentation/docs/helpers.html">Helpers & Utility Functions — src/helpers</a>
<a href="documentation/docs/coffee-script.html">The CoffeeScript Module — src/coffee-script</a>
<a href="documentation/docs/cake.html">Cake & Cakefiles — src/cake</a>
<a href="documentation/docs/command.html">"coffee" Command-Line Utility — src/command</a>
<a href="documentation/docs/optparse.html">Option Parsing — src/optparse</a>
<a href="documentation/docs/repl.html">Interactive REPL — src/repl</a>
</div>
</div>
<div id="error" style="display:none;"></div>
</div>
<div class="container">
<span class="bookmark" id="top"></span>
<p>
CoffeeScript is a little language that compiles into JavaScript. Think
of it as JavaScript's less ostentatious kid brother — the same genes,
roughly the same height, but a different sense of style. Apart from a handful of
bonus goodies, statements in CoffeeScript correspond one-to-one with their
equivalent in JavaScript, it's just another way of saying it.
</p>
<p>
<b>Disclaimer:</b>
CoffeeScript is just for fun. Until it reaches 1.0, <i>there are no guarantees
that the syntax won't change between versions.</i> That said,
it compiles into clean JavaScript (the good parts) that can use existing
JavaScript libraries seamlessly, and passes through
<a href="http://www.jslint.com/">JSLint</a> without warnings. The compiled
output is quite readable — pretty-printed, with comments
preserved intact.
</p>
<p>
<b>Latest Version:</b>
<a href="http://github.com/jashkenas/coffee-script/tarball/0.6.2">0.6.2</a>
</p>
<h2>
<span id="overview" class="bookmark"></span>
Mini Overview
</h2>
<p><i>CoffeeScript on the left, compiled JavaScript output on the right.</i></p>
<%= code_for('overview', 'cubed_list') %>
<p>
For a longer CoffeeScript example, check out
<a href="documentation/docs/underscore.html">Underscore.coffee</a>, a port
of the <a href="http://documentcloud.github.com/underscore/">Underscore.js</a>
library of helper functions. Underscore.coffee can pass the entire Underscore.js
test suite. The CoffeeScript version is faster than the original for a number
of methods (in general, due to the speed of CoffeeScript's array comprehensions), and
after being minified and gzipped, is only 241 bytes larger than the original
JavaScript version.
Additional examples are included in the source repository, inside the
<a href="http://github.com/jashkenas/coffee-script/tree/master/examples/">examples</a> folder.
</p>
<h2>
<span id="installation" class="bookmark"></span>
Installation and Usage
</h2>
<p>
The CoffeeScript compiler is written in pure CoffeeScript, using a
<a href="documentation/docs/grammar.html">small DSL</a>
on top of the <a href="http://github.com/zaach/jison">Jison parser generator</a>, and is available
as a <a href="http://nodejs.org/">Node.js</a> utility. The core compiler however,
does not depend on Node, and can be run in other server-side-JavaScript environments,
or in the browser (see "Try CoffeeScript", above). This may be helpful,
as Node only run on flavors of nix, and not Windows, for the time being.
</p>
<p>
To install, first make sure you have a working copy of the latest tagged version of
<a href="http://nodejs.org/">Node.js</a>, currently <b>0.1.90</b> or higher.
Then clone the CoffeeScript
<a href="http://github.com/jashkenas/coffee-script">source repository</a>
from GitHub, or download the latest
release: <a href="http://github.com/jashkenas/coffee-script/tarball/0.6.2">0.6.2</a>.
To install the CoffeeScript compiler system-wide
under <tt>/usr/local</tt>, open the directory and run:
</p>
<pre>
sudo bin/cake install</pre>
<p>
This provides the <tt>coffee</tt> command, which will execute CoffeeScripts
under Node.js by default, but is also used to compile CoffeeScript
<tt>.coffee</tt> files into JavaScript, or to run an an interactive REPL.
When compiling to JavaScript, <tt>coffee</tt> writes the output
as <tt>.js</tt> files in the same directory by default, but output
can be customized with the following options:
</p>
<table>
<tr>
<td><code>-c, --compile</code></td>
<td>
Compile a <tt>.coffee</tt> script into a <tt>.js</tt> JavaScript file
of the same name.
</td>
</tr>
<tr>
<td width="25%"><code>-i, --interactive</code></td>
<td>
Launch an interactive CoffeeScript session to try short snippets.
More pleasant if wrapped with
<a href="http://utopia.knoware.nl/~hlub/uck/rlwrap/rlwrap.html">rlwrap</a>.
</td>
</tr>
<tr>
<td><code>-o, --output [DIR]</code></td>
<td>
Write out all compiled JavaScript files into the specified directory.
Use in conjunction with <tt>--compile</tt> or <tt>--watch</tt>.
</td>
</tr>
<tr>
<td><code>-w, --watch</code></td>
<td>
Watch the modification times of the coffee-scripts, recompiling as
soon as a change occurs.
</td>
</tr>
<tr>
<td><code>-p, --print</code></td>
<td>
Instead of writing out the JavaScript as a file, print it
directly to <b>stdout</b>.
</td>
</tr>
<tr>
<td><code>-l, --lint</code></td>
<td>
If the <tt>jsl</tt>
(<a href="http://www.javascriptlint.com/">JavaScript Lint</a>)
command is installed, use it
to check the compilation of a CoffeeScript file. (Handy in
conjunction with <tt>--watch</tt>)
</td>
</tr>
<tr>
<td><code>-s, --stdio</code></td>
<td>
Pipe in CoffeeScript to STDIN and get back JavaScript over STDOUT.
Good for use with processes written in other languages. An example:<br />
<tt>cat src/cake.coffee | coffee -sc</tt>
</td>
</tr>
<tr>
<td><code>-e, --eval</code></td>
<td>
Compile and print a little snippet of CoffeeScript directly from the
command line. For example:<br /><tt>coffee -e "puts num for num in [10..1]"</tt>
</td>
</tr>
<tr>
<td><code>--no-wrap</code></td>
<td>
Compile the JavaScript without the top-level function safety wrapper.
(Used for CoffeeScript as a Node.js module.)
</td>
</tr>
<tr>
<td><code>-t, --tokens</code></td>
<td>
Instead of parsing the CoffeeScript, just lex it, and print out the
token stream: <tt>[IDENTIFIER square] [ASSIGN :] [PARAM_START (]</tt> ...
</td>
</tr>
<tr>
<td><code>-n, --nodes</code></td>
<td>
Instead of compiling the CoffeeScript, just lex and parse it, and print
out the parse tree:
<pre class="no_bar">
Expressions
Assign
Value "square"
Code "x"
Op *
Value "x"
Value "x"</pre>
</td>
</tr>
</table>
<p>
<b>Examples:</b>
</p>
<pre>
coffee -c path/to/script.coffee
coffee --interactive
coffee --watch --lint experimental.coffee
coffee --print app/scripts/*.coffee > concatenation.js</pre>
<h2>
<span id="language" class="bookmark"></span>
Language Reference
</h2>
<p>
<i>
This reference is structured so that it can be read from top to bottom,
if you like. Later sections use ideas and syntax previously introduced.
Familiarity with JavaScript is assumed.
In all of the following examples, the source CoffeeScript is provided on
the left, and the direct compilation into JavaScript is on the right.
</i>
</p>
<p>
<i>
Many of the examples can be run (where it makes sense) by pressing the "run"
button towards the bottom right. You can also paste examples into
"Try CoffeeScript" in the toolbar, and play with them from there.
</i>
<p>
<span id="whitespace" class="bookmark"></span>
<b class="header">Significant Whitespace</b>
CoffeeScript uses Python-style significant whitespace: You don't need to
use semicolons <tt>;</tt> to terminate expressions, ending
the line will do just as well. Semicolons can still be used to fit
multiple expressions onto a single line. Instead of using curly braces
<tt>{ }</tt> to delimit blocks of code (like <a href="#functions">functions</a>,
<a href="#conditionals">if-statements</a>,
<a href="#switch">switch</a>, and <a href="#try">try/catch</a>),
use indentation.
</p>
<p>
You don't need to use parentheses to invoke a function if you're passing
arguments:<br /><tt>print "coffee"</tt>
</p>
<p>
You can use newlines to break up your expression into smaller pieces,
as long as CoffeeScript can determine that the line hasn't finished yet,
because it ends with an operator or a dot.
</p>
<p>
<span id="functions" class="bookmark"></span>
<b class="header">Functions and Invocation</b>
Functions are defined by a list of parameters, an arrow, and the
function body. The empty function looks like this: <tt>-></tt> All
functions in CoffeeScript are named by default, for easier debugging.
</p>
<%= code_for('functions', 'cube(5)') %>
<p>
If you'd like to assign a function literal to a variable, but not have
it be named, just wrap the function definition in parentheses:
<tt>((x) -> x * x)</tt>
</p>
<p>
<span id="assignment" class="bookmark"></span>
<b class="header">Assignment</b>
Use a colon <tt>:</tt> to assign, as in
<a href="http://json.org">JSON</a>. Equal signs are only needed for
mathy things. While colons are preferred, the two may be used interchangeably,
even within object literals.
</p>
<%= code_for('assignment', 'greeting') %>
<p>
All declaration of new variables is pushed up to the top of the nearest
lexical scope, so that assignment may always be performed within expressions.
</p>
<p>
<span id="objects_and_arrays" class="bookmark"></span>
<b class="header">Objects and Arrays</b>
Object and Array literals look very similar to their JavaScript cousins.
When you spread out each assignment on a separate line, the commas are
optional. In this way, assigning object properties looks the same as
assigning local variables, and can be moved around freely. Feel free to mix
and match the two styles.
</p>
<%= code_for('objects_and_arrays', 'song.join(",")') %>
<p>
<span id="lexical_scope" class="bookmark"></span>
<b class="header">Lexical Scoping and Variable Safety</b>
The CoffeeScript compiler takes care to make sure that all of your variables
are properly declared within lexical scope — you never need to write
<tt>var</tt> yourself.
</p>
<%= code_for('scope', 'new_num') %>
<p>
Notice how the all of the variable declarations have been pushed up to
the top of the closest scope, the first time they appear.
<b>num</b> is not redeclared within the inner function, because it's
already in scope; the <b>new_num</b> within the function, on the other hand,
should not be able to change the value of the external variable of the same name, and
therefore has a declaration of its own.
</p>
<p>
This behavior is effectively identical to Ruby's scope for local variables.
Because you don't have direct access to the <tt>var</tt> keyword,
it's impossible to shadow an outer variable on purpose, you may only refer
to it. So be careful that you're not reusing the name of an external
variable accidentally, if you're writing a deeply nested function.
</p>
<p>
Although suppressed within this documentation for clarity, all
CoffeeScript output is wrapped in an anonymous function:
<tt>(function(){ ... })();</tt> This safety wrapper, combined with the
automatic generation of the <tt>var</tt> keyword, make it exceedingly difficult
to pollute the global namespace by accident.
</p>
<p>
If you'd like to create top-level variables for other scripts to use,
attach them as properties on <b>window</b>, or on the <b>exports</b>
object in CommonJS. The <b>existential operator</b> (below), gives you a
reliable way to figure out where to add them, if you're targeting both
CommonJS and the browser: <tt>root: exports ? this</tt>
</p>
<p>
<span id="conditionals" class="bookmark"></span>
<b class="header">Conditionals, Ternaries, and Conditional Assignment</b>
<b>If/else</b> statements can be written without the use of parentheses and
curly brackets. As with functions and other block expressions,
multi-line conditionals are delimited by indentation. There's also a handy
postfix form, with the <tt>if</tt> or <tt>unless</tt> at the end.
</p>
<p>
CoffeeScript will compile <b>if</b> statements using the ternary operator
when possible, to make it easier to use the result as an expression.
</p>
<%= code_for('conditionals') %>
<p>
You can assign a variable to a half-expression to perform an operation
like Ruby's <tt>||=</tt>, which only assigns a value to a variable
if the variable's current value is falsy.
</p>
<p>
<span id="aliases" class="bookmark"></span>
<b class="header">Aliases</b>
Because the <tt>==</tt> operator frequently causes undesirable coercion,
is intransitive, and has a different meaning than in other languages,
CoffeeScript compiles <tt>==</tt> into <tt>===</tt>, and <tt>!=</tt> into
<tt>!==</tt>.
In addition, <tt>is</tt> compiles into <tt>===</tt>,
and <tt>isnt</tt> into <tt>!==</tt>.
</p>
<p>
You can use <tt>not</tt> as an alias for <tt>!</tt>.
</p>
<p>
For logic, <tt>and</tt> compiles to <tt>&&</tt>, and <tt>or</tt>
into <tt>||</tt>.
</p>
<p>
Instead of a newline or semicolon, <tt>then</tt> can be used to separate
conditions from expressions, in <b>while</b>,
<b>if</b>/<b>else</b>, and <b>switch</b>/<b>when</b> statements.
</p>
<p>
As in <a href="http://yaml.org/">YAML</a>, <tt>on</tt> and <tt>yes</tt>
are the same as boolean <tt>true</tt>, while <tt>off</tt> and <tt>no</tt> are boolean <tt>false</tt>.
</p>
<p>
For single-line statements, <tt>unless</tt> can be used as the inverse of <tt>if</tt>.
</p>
<p>
As a shortcut for <tt>this.property</tt>, you can use <tt>@property</tt>.
</p>
<%= code_for('aliases') %>
<p>
<span id="splats" class="bookmark"></span>
<b class="header">Splats...</b>
The JavaScript <b>arguments object</b> is a useful way to work with
functions that accept variable numbers of arguments. CoffeeScript provides
splats <tt>...</tt>, both for function definition as well as invocation,
making variable numbers of arguments a little bit more palatable.
</p>
<%= code_for('splats', true) %>
<p>
<span id="while" class="bookmark"></span>
<b class="header">While & Until Loops</b>
The only low-level loop that CoffeeScript provides is the <b>while</b> loop. The
main difference from JavaScript is that the <b>while</b> loop can be used
as an expression, returning an array containing the result of each iteration
through the loop.
</p>
<%= code_for('while', 'lyrics.join("\n")') %>
<p>
For readability, the <b>until</b> loop serves as an inverted <b>while</b> loop.
Other JavaScript loops, such as <b>for</b> loops and <b>do-while</b> loops
can be mimicked by variations on <b>while</b>, but the hope is that you
won't need to do that with CoffeeScript, either because you're using
<b>each</b> (<b>forEach</b>) style iterators, or...
</p>
<p>
<span id="comprehensions" class="bookmark"></span>
<b class="header">Comprehensions (Arrays, Objects, and Ranges)</b>
For your looping needs, CoffeeScript provides array comprehensions
similar to Python's. They replace (and compile into) <b>for</b> loops, with
optional guard clauses and the value of the current array index.
Unlike for loops, array comprehensions are expressions, and can be returned
and assigned. They should be able to handle most places where you otherwise
would use a loop, <b>each</b>/<b>forEach</b>, <b>map</b>, or <b>select</b>/<b>filter</b>.
</p>
<%= code_for('array_comprehensions') %>
<p>
If you know the start and end of your loop, or would like to step through
in fixed-size increments, you can use a range to specify the start and
end of your comprehension. (The long line-breaking "for" definitions in
the compiled JS below allow ranges to count downwards, as well as upwards).
</p>
<%= code_for('range_comprehensions', 'countdown') %>
<p>
Comprehensions can also be used to iterate over the keys and values in
an object. Use <tt>of</tt> to signal comprehension over the properties of
an object instead of the values in an array.
</p>
<%= code_for('object_comprehensions', 'ages.join(", ")') %>
<p>
<span id="slice_splice" class="bookmark"></span>
<b class="header">Array Slicing and Splicing with Ranges</b>
CoffeeScript borrows Ruby's
<a href="http://ruby-doc.org/core/classes/Range.html">range syntax</a>
for extracting slices of arrays. With two dots (<tt>3..5</tt>), the range
is inclusive: the first argument is the index of the first element in
the slice, and the second is the index of the last one. Three dots signify
a range that excludes the end.
</p>
<%= code_for('slices', 'numbers_copy') %>
<p>
The same syntax can be used with assignment to replace a segment of an
array with new values (to splice it).
</p>
<%= code_for('splices', 'numbers') %>
<p>
<span id="expressions" class="bookmark"></span>
<b class="header">Everything is an Expression (at least, as much as possible)</b>
You might have noticed how even though we don't add return statements
to CoffeeScript functions, they nonetheless return their final value.
The CoffeeScript compiler tries to make sure that all statements in the
language can be used as expressions. Watch how the <tt>return</tt> gets
pushed down into each possible branch of execution, in the function
below.
</p>
<%= code_for('expressions', 'eldest') %>
<p>
Even though functions will always return their final value, it's both possible
and encouraged to return early from a function body writing out the explicit
return (<tt>return value</tt>), when you know that you're done.
</p>
<p>
Because variable declarations occur at the top of scope, assignment can
be used within expressions, even for variables that haven't been seen before:
</p>
<%= code_for('expressions_assignment', 'six') %>
<p>
Things that would otherwise be statements in JavaScript, when used
as part of an expression in CoffeeScript, are converted into expressions
by wrapping them in a closure. This lets you do useful things, like assign
the result of a comprehension to a variable:
</p>
<%= code_for('expressions_comprehension', 'globals') %>
<p>
As well as silly things, like passing a <b>try/catch</b> statement directly
into a function call:
</p>
<%= code_for('expressions_try', true) %>
<p>
There are a handful of statements in JavaScript that can't be meaningfully
converted into expressions, namely <tt>break</tt>, <tt>continue</tt>,
and <tt>return</tt>. If you make use of them within a block of code,
CoffeeScript won't try to perform the conversion.
</p>
<p>
<span id="existence" class="bookmark"></span>
<b class="header">The Existential Operator</b>
It's a little difficult to check for the existence of a variable in
JavaScript. <tt>if (variable) ...</tt> comes close, but fails for zero,
the empty string, and false. CoffeeScript's existential operator <tt>?</tt> returns true unless
a variable is <b>null</b> or <b>undefined</b>, which makes it analogous
to Ruby's <tt>nil?</tt>
</p>
<p>
It can also be used for safer conditional assignment than <tt>||=</tt>
provides, for cases where you may be handling numbers or strings.
</p>
<%= code_for('existence', 'speed') %>
<p>
The accessor variant of the existential operator <tt>?.</tt> can be used to soak
up null references in a chain of properties. Use it instead
of the dot accessor <tt>.</tt> in cases where the base value may be <b>null</b>
or <b>undefined</b>. If all of the properties exist then you'll get the expected
result, if the chain is broken, <b>undefined</b> is returned instead of
the <b>TypeError</b> that would be raised otherwise.
</p>
<%= code_for('soaks') %>
<p>
Soaking up nulls is similar to Ruby's
<a href="http://andand.rubyforge.org/">andand gem</a>, and to the
<a href="http://groovy.codehaus.org/Operators#Operators-SafeNavigationOperator%28%3F.%29">safe navigation operator</a>
in Groovy.
</p>
<p>
<span id="classes" class="bookmark"></span>
<b class="header">Classes, Inheritance, and Super</b>
JavaScript's prototypal inheritance has always been a bit of a
brain-bender, with a whole family tree of libraries that provide a cleaner
syntax for classical inheritance on top of JavaScript's prototypes:
<a href="http://code.google.com/p/base2/">Base2</a>,
<a href="http://prototypejs.org/">Prototype.js</a>,
<a href="http://jsclass.jcoglan.com/">JS.Class</a>, etc.
The libraries provide syntactic sugar, but the built-in inheritance would
be completely usable if it weren't for a couple of small exceptions:
it's awkward to call <b>super</b> (the prototype object's
implementation of the current function), and it's awkward to correctly
set the prototype chain.
</p>
<p>
Instead of repetitively attaching functions to a prototype, CoffeeScript
provides a basic <tt>class</tt> structure that allows you to name your class,
set the superclass, assign prototypal properties, and define the constructor,
in a single assignable expression.
</p>
<%= code_for('classes', true) %>
<p>
If structuring your prototypes classically isn't your cup of tea, CoffeeScript
provides a couple of lower-level conveniences. The <tt>extends</tt> operator
helps with proper prototype setup, <tt>::</tt> gives you
quick access to an object's prototype, and <tt>super()</tt>
is converted into a call against the immediate ancestor's method of the same name.
</p>
<%= code_for('prototypes', '"one_two".dasherize()') %>
<p>
Finally, you may assign Class-level (static) properties within a class
definition by using<br /><tt>@property: value</tt>
</p>
<p>
<span id="pattern_matching" class="bookmark"></span>
<b class="header">Pattern Matching (Destructuring Assignment)</b>
To make extracting values from complex arrays and objects more convenient,
CoffeeScript implements ECMAScript Harmony's proposed
<a href="http://wiki.ecmascript.org/doku.php?id=harmony:destructuring">destructuring assignment</a>
syntax. When you assign an array or object literal to a value, CoffeeScript
breaks up and matches both sides against each other, assigning the values
on the right to the variables on the left. In the simplest case, it can be
used for parallel assignment:
</p>
<%= code_for('parallel_assignment', 'bait') %>
<p>
But it's also helpful for dealing with functions that return multiple
values.
</p>
<%= code_for('multiple_return_values', 'forecast') %>
<p>
Pattern matching can be used with any depth of array and object nesting,
to help pull out deeply nested properties.
</p>
<%= code_for('object_extraction', 'name + " — " + street') %>
<p>
Pattern matching can even be combined with splats.
</p>
<%= code_for('patterns_and_splats', 'contents.join("")') %>
<p>
<span id="fat_arrow" class="bookmark"></span>
<b class="header">Function binding</b>
In JavaScript, the <tt>this</tt> keyword is dynamically scoped to mean the
object that the current function is attached to. If you pass a function as
as callback, or attach it to a different object, the original value of <tt>this</tt>
will be lost. If you're not familiar with this behavior,
<a href="http://www.digital-web.com/articles/scope_in_javascript/">this Digital Web article</a>
gives a good overview of the quirks.
</p>
<p>
The fat arrow <tt>=></tt> can be used to both define a function, and to bind
it to the current value of <tt>this</tt>, right on the spot. This is helpful
when using callback-based libraries like Prototype or jQuery, for creating
iterator functions to pass to <tt>each</tt>, or event-handler functions
to use with <tt>bind</tt>. Functions created with the fat arrow are able to access
properties of the <tt>this</tt> where they're defined.
</p>
<%= code_for('fat_arrow') %>
<p>
If we had used <tt>-></tt> in the callback above, <tt>@customer</tt> would
have referred to the undefined "customer" property of the DOM element,
and trying to call <tt>purchase()</tt> on it would have raised an exception.
</p>
<p>
If you have more custom needs for function binding, CoffeeScript includes
the <tt><-</tt> bind operator, which works the same as ECMAScript 5
and Prototype.js's <tt>Function#bind</tt>. The first argument is the <tt>this</tt>
value, and the remainder are curried arguments. In the example below,
we curry a jQuery request for a URL, and then execute the bound function
with the missing callback argument.
</p>
<%= code_for('binding', true) %>
<p>
<span id="embedded" class="bookmark"></span>
<b class="header">Embedded JavaScript</b>
Hopefully, you'll never need to use it, but if you ever need to intersperse
snippets of JavaScript within your CoffeeScript, you can
use backticks to pass it straight through.
</p>
<%= code_for('embedded', 'hi()') %>
<p>
<span id="switch" class="bookmark"></span>
<b class="header">Switch/When/Else</b>
<b>Switch</b> statements in JavaScript are rather broken. You can only
do comparisons based on string equality, and need to remember to <b>break</b> at the end of
every <b>case</b> statement to avoid accidentally falling through to
the default case. CoffeeScript compiles <b>switch</b> statements into JavaScript if-else chains, allowing you to
compare any object (via <b>===</b>), preventing fall-through, and resulting
in a returnable, assignable expression. The format is: <tt>switch</tt> condition,
<tt>when</tt> clauses, <tt>else</tt> the default case.
</p>
<p>
As in Ruby, <b>switch</b> statements in CoffeeScript can take multiple
values for each <b>when</b> clause. If any of the values match, the clause
runs.
</p>
<%= code_for('switch') %>
<p>
<span id="try" class="bookmark"></span>
<b class="header">Try/Catch/Finally</b>
Try/catch statements are just about the same as JavaScript (although
they work as expressions).
</p>
<%= code_for('try') %>
<p>
<span id="comparisons" class="bookmark"></span>
<b class="header">Chained Comparisons</b>
CoffeeScript borrows
<a href="http://docs.python.org/reference/expressions.html#notin">chained comparisons</a>
from Python — making it easy to test if a value falls within a
certain range.
</p>
<%= code_for('comparisons', 'healthy') %>
<p>
<span id="interpolation" class="bookmark"></span>
<b class="header">String and RegExp Interpolation</b>
A version of <a href="http://wiki.ecmascript.org/doku.php?id=strawman:string_interpolation">ECMAScript Harmony's proposed string interpolation</a>
is included in CoffeeScript. Simple variables can be included by marking
them with a dollar sign.
</p>
<%= code_for('interpolation', 'quote') %>
<p>
And arbitrary expressions can be interpolated by using brackets <tt>${ ... }</tt><br />
Interpolation works the same way within regular expressions.
</p>
<%= code_for('interpolation_expression', 'sentence') %>
<p>
<span id="strings" class="bookmark"></span>
<b class="header">Multiline Strings and Heredocs</b>
Multiline strings are allowed in CoffeeScript.
</p>
<%= code_for('strings', 'moby_dick') %>
<p>
Heredocs can be used to hold formatted or indentation-sensitive text
(or, if you just don't feel like escaping quotes and apostrophes). The
indentation level that begins the heredoc is maintained throughout, so
you can keep it all aligned with the body of your code.
</p>
<%= code_for('heredocs') %>
<p>
Double-quoted heredocs, like double-quoted strings, allow interpolation.
</p>
<h2>
<span id="cake" class="bookmark"></span>
Cake, and Cakefiles
</h2>
<p>
CoffeeScript includes a simple build system similar to Make and Rake. Naturally,
it's called Cake, and is used for the build and test tasks for the CoffeeScript
language itself. Tasks are defined in a file named <tt>Cakefile</tt>, and
can be invoked by running <tt>cake taskname</tt> from within the directory.
To print a list of all the tasks, just run <tt>cake</tt>.
</p>
<p>
Task definitions are written in CoffeeScript, so you can put arbitrary code
in your Cakefile. Define a task with a name, a long description, and the
function to invoke when the task is run. Here's a hypothetical task
that uses the Node.js API.
</p>
<%= code_for('cake_tasks') %>
<h2>
<span id="scripts" class="bookmark"></span>
"text/coffeescript" Script Tags
</h2>
<p>
While it's not recommended for serious use, CoffeeScripts may be included
directly within the browser using <tt><script type="text/coffeescript"></tt>
tags. The source includes a compressed and minified version of the compiler
(<a href="extras/coffee-script.js">Download current version here, 43k when gzipped</a>)
as <tt>extras/coffee-script.js</tt>. Include this file on a page with
inline CoffeeScript tags, and it will compile and evaluate them in order.
</p>
<p>
In fact, the little bit of glue script that runs "Try CoffeeScript" above,
as well as jQuery for the menu, is implemented in just this way.
View source and look at the bottom of the page to see the example.
Including the script also gives you access to <tt>CoffeeScript.compile()</tt>
so you can pop open Firebug and try compiling some strings.
</p>
<p>
The usual caveats about CoffeeScript apply — your inline scripts will
run within a closure wrapper, so if you want to expose global variables or
functions, attach them to the <tt>window</tt> object.
</p>
<h2>
<span id="resources" class="bookmark"></span>
Resources
</h2>
<ul>
<li>
<a href="http://github.com/jashkenas/coffee-script/">Source Code</a><br />
Use <tt>bin/coffee</tt> to test your changes,<br />
<tt>bin/cake test</tt> to run the test suite,<br />
<tt>bin/cake build</tt> to rebuild the CoffeeScript compiler, and <br />
<tt>bin/cake build:parser</tt> to regenerate the Jison parser if you're
working on the grammar. <br /><br />
<tt>git checkout lib && bin/cake build:full</tt> is a good command to run when you're working
on the core language. It'll refresh the lib directory
(in case you broke something), build your altered compiler, use that to
rebuild itself (a good sanity test) and then run all of the tests. If
they pass, there's a good chance you've made a successful change.
</li>
<li>
<a href="http://github.com/jashkenas/coffee-script/issues">CoffeeScript Issues</a><br />
Bugs reports, feature requests, and general discussion all belong here.
</li>
<li>
If you'd like to chat, stop by <tt>#coffeescript</tt> on Freenode in the
IRC client of your choice, or on
<a href="http://webchat.freenode.net/">webchat.freenode.net</a>.
</li>
<li>
<b>yeungda</b>'s <a href="http://github.com/yeungda/jcoffeescript">JCoffeeScript</a>
— A Java Library that uses Rhino to compile CoffeeScript, allowing
compilation within Java projects or on systems that Node.js doesn't support.
</li>
<li>
<b>defunkt</b>'s <a href="http://github.com/defunkt/coffee-mode">CoffeeScript Major Mode</a>
— a Emacs major mode that provides syntax highlighting, indentation
support, and some bonus commands.
</li>
<li>
<b>jashkenas</b>'s <a href="http://github.com/jashkenas/coffee-script-tmbundle">CoffeeScript TextMate Bundle</a>
— which provides syntax highlighting, snippet expansion, and the
ability to run bits of CoffeeScript from within TextMate itself.
</li>
<li>
<b>kchmck</b>'s <a href="http://github.com/kchmck/vim-coffee-script">Vim CoffeeScript</a>
— which adds Vim syntax highlighting and indentation support.
</li>
<li>
<b>yeungda</b>'s <a href="http://yeungda.github.com/coffeescript-idea/">coffeescript-idea</a>
— a plugin for IntelliJ IDEA and RubyMine providing syntax highlighting.
</li>
<li>
<b>mattly</b>'s <a href="http://github.com/mattly/rack-coffee">rack-coffee</a>
— a small Rack middleware for serving CoffeeScript files as
compiled JavaScript on the fly.
</li>
<li>
<b>jnicklas</b>'s <a href="http://github.com/jnicklas/bistro_car">BistroCar</a>
— a plugin that serves and bundles CoffeeScript from within your
Rails application.
</li>
<li>
<b>sutto</b>'s <a href="http://github.com/Sutto/barista">Barista</a>
— a BistroCar alternative that integrates well with
<a href="http://documentcloud.github.com/jammit">Jammit</a> and Rails 3.
</li>
<li>
<b>inem</b> and <b>gerad</b>'s <a href="http://github.com/gerad/coffee-haml-filter">coffee-haml-filter</a>
— a custom filter for rendering CoffeeScript inline within
<a href="http://haml-lang.com/">HAML</a> templates.
</li>
</ul>
<h2>
<span id="webchat" class="bookmark"></span>
Web Chat (IRC)
</h2>
<p>
Quick help and advice can usually be found in the CoffeeScript IRC room.
Join <tt>#coffeescript</tt> on <tt>irc.freenode.net</tt>, or click the
button below to open a webchat session on this page.
</p>
<p>
<button id="open_webchat">click to open #coffeescript</button>
</p>
<h2>
<span id="change_log" class="bookmark"></span>
Change Log
</h2>
<p>
<b class="header" style="margin-top: 20px;">0.6.2</b>
The <tt>coffee</tt> command will now preserve directory structure when
compiling a directory full of scripts. Fixed two omissions that were preventing
the CoffeeScript compiler from running live within Internet Explorer.
There's now a syntax for block comments, similar in spirit to CoffeeScript's heredocs.
ECMA Harmony DRY-style pattern matching is now supported, where the name
of the property is the same as the name of the value: <tt>{name, length}: func</tt>.
Pattern matching is now allowed within comprehension variables. <tt>unless</tt>
is now allowed in block form. <tt>until</tt> loops were added, as the inverse
of <tt>while</tt> loops. <tt>switch</tt> statements are now allowed without
switch object clauses. Compatible
with Node.js <b>v0.1.95</b>.
</p>
<p>
<b class="header" style="margin-top: 20px;">0.6.1</b>
Upgraded CoffeeScript for compatibility with the new Node.js <b>v0.1.90</b>
series.
</p>
<p>
<b class="header" style="margin-top: 20px;">0.6.0</b>
Trailing commas are now allowed, a-la Python. Static
properties may be assigned directly within class definitions,
using <tt>@property</tt> notation.
</p>
<p>
<b class="header" style="margin-top: 20px;">0.5.6</b>
Interpolation can now be used within regular expressions and heredocs, as well as
strings. Added the <tt><-</tt> bind operator.
Allowing assignment to half-expressions instead of special <tt>||=</tt>-style
operators. The arguments object is no longer automatically converted into
an array. After requiring <tt>coffee-script</tt>, Node.js can now directly
load <tt>.coffee</tt> files, thanks to <b>registerExtension</b>. Multiple
splats can now be used in function calls, arrays, and pattern matching.
</p>
<p>
<b class="header" style="margin-top: 20px;">0.5.5</b>
String interpolation, contributed by
<a href="http://github.com/StanAngeloff">Stan Angeloff</a>.
Since <tt>--run</tt> has been the default since <b>0.5.3</b>, updating
<tt>--stdio</tt> and <tt>--eval</tt> to run by default, pass <tt>--compile</tt>
as well if you'd like to print the result.
</p>
<p>
<b class="header" style="margin-top: 20px;">0.5.4</b>
Bugfix that corrects the Node.js global constants <tt>__filename</tt> and
<tt>__dirname</tt>. Tweaks for more flexible parsing of nested function
literals and improperly-indented comments. Updates for the latest Node.js API.
</p>
<p>
<b class="header" style="margin-top: 20px;">0.5.3</b>
CoffeeScript now has a syntax for defining classes. Many of the core
components (Nodes, Lexer, Rewriter, Scope, Optparse) are using them.
Cakefiles can use <tt>optparse.coffee</tt> to define options for tasks.
<tt>--run</tt> is now the default flag for the <tt>coffee</tt> command,
use <tt>--compile</tt> to save JavaScripts. Bugfix for an ambiguity between
RegExp literals and chained divisions.
</p>
<p>
<b class="header" style="margin-top: 20px;">0.5.2</b>
Added a compressed version of the compiler for inclusion in web pages as
<br /><tt>extras/coffee-script.js</tt>. It'll automatically run any script tags
with type <tt>text/coffeescript</tt> for you. Added a <tt>--stdio</tt> option
to the <tt>coffee</tt> command, for piped-in compiles.
</p>