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<!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">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="#objects_and_arrays">Objects and Arrays</a>
<a href="#lexical_scope">Lexical Scoping and Variable Safety</a>
<a href="#conditionals">If, Else, Unless, and Conditional Assignment</a>
<a href="#aliases">Aliases</a>
<a href="#splats">Splats...</a>
<a href="#while">While, Until, and Loop</a>
<a href="#comprehensions">Comprehensions (Arrays, Objects, and Ranges)</a>
<a href="#slices">Array Slicing and Splicing</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">The Switch Statement</a>
<a href="#try">Try/Catch/Finally</a>
<a href="#comparisons">Chained Comparisons</a>
<a href="#strings">String Interpolation, Heredocs, and Block Comments</a>
<a href="#regexes">Extended Regular Expressions</a>
<a href="#cake">Cake, and Cakefiles</a>
<a href="#scripts">"text/coffeescript" Script Tags</a>
<a href="#examples">Examples</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" rows="100">alert "Hello CoffeeScript!"</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. Underneath
all of those embarrassing braces and semicolons, JavaScript has always had
a gorgeous object model at its heart. CoffeeScript is an attempt to expose
the good parts of JavaScript in a simple way.
</p>
<p>
The golden rule of CoffeeScript is: <i>"It's just JavaScript"</i>. The code
compiles one-to-one into the equivalent JS, and there is
no interpretation at runtime. You can use any existing JavaScript library
seamlessly (and vice-versa). The compiled output is readable and pretty-printed,
passes through <a href="http://www.javascriptlint.com/">JavaScript Lint</a>
without warnings, and can be run by any JavaScript implementation.
</p>
<p>
<b>Latest Version:</b>
<a href="http://github.com/jashkenas/coffee-script/tarball/0.9.6">0.9.6</a>
</p>
<h2>
<span id="overview" class="bookmark"></span>
Overview
</h2>
<p><i>CoffeeScript on the left, compiled JavaScript output on the right.</i></p>
<div class='code'><pre class="idle"><span class="Comment"><span class="Comment">#</span> Assignment:</span>
number <span class="Keyword">=</span> <span class="Number">42</span>
opposite <span class="Keyword">=</span> <span class="BuiltInConstant">true</span>
<span class="Comment"><span class="Comment">#</span> Conditions:</span>
number <span class="Keyword">=</span> <span class="Keyword">-</span><span class="Number">42</span> <span class="Keyword">if</span> opposite
<span class="Comment"><span class="Comment">#</span> Functions:</span>
<span class="FunctionName">square </span><span class="Keyword">=</span> <span class="FunctionArgument">(x)</span> <span class="Storage">-></span> x <span class="Keyword">*</span> x
<span class="Comment"><span class="Comment">#</span> Arrays:</span>
list <span class="Keyword">=</span> [<span class="Number">1</span>, <span class="Number">2</span>, <span class="Number">3</span>, <span class="Number">4</span>, <span class="Number">5</span>]
<span class="Comment"><span class="Comment">#</span> Objects:</span>
math <span class="Keyword">=</span>
root: Math.sqrt
square: square
<span class="FunctionName">cube</span><span class="Keyword">:</span> <span class="FunctionArgument">(x)</span> <span class="Storage">-></span> x <span class="Keyword">*</span> square x
<span class="Comment"><span class="Comment">#</span> Splats:</span>
<span class="FunctionName">race </span><span class="Keyword">=</span> <span class="FunctionArgument">(winner, runners...)</span> <span class="Storage">-></span>
print winner, runners
<span class="Comment"><span class="Comment">#</span> Existence:</span>
alert <span class="String"><span class="String">"</span>I knew it!<span class="String">"</span></span> <span class="Keyword">if</span> elvis<span class="Keyword">?</span>
<span class="Comment"><span class="Comment">#</span> Array comprehensions:</span>
cubes <span class="Keyword">=</span> (math.cube num <span class="Keyword">for</span> num <span class="Keyword">in</span> list)
</pre><pre class="idle"><span class="Storage">var</span> cubes, list, math, num, number, opposite, race, square, _i, _len, _results;
<span class="Storage">var</span> __slice <span class="Keyword">=</span> <span class="LibraryClassType">Array</span>.<span class="LibraryConstant">prototype</span>.slice;
number <span class="Keyword">=</span> <span class="Number">42</span>;
opposite <span class="Keyword">=</span> <span class="BuiltInConstant">true</span>;
<span class="Keyword">if</span> (opposite) {
number <span class="Keyword">=</span> <span class="Keyword">-</span><span class="Number">42</span>;
}
<span class="FunctionName">square</span> = <span class="Storage">function</span>(<span class="FunctionArgument">x</span>) {
<span class="Keyword">return</span> x <span class="Keyword">*</span> x;
};
list <span class="Keyword">=</span> [<span class="Number">1</span>, <span class="Number">2</span>, <span class="Number">3</span>, <span class="Number">4</span>, <span class="Number">5</span>];
math <span class="Keyword">=</span> {
root: <span class="LibraryClassType">Math</span>.sqrt,
square: square,
<span class="FunctionName">cube</span>: <span class="Storage">function</span>(<span class="FunctionArgument">x</span>) {
<span class="Keyword">return</span> x <span class="Keyword">*</span> square(x);
}
};
<span class="FunctionName">race</span> = <span class="Storage">function</span>() {
<span class="Storage">var</span> runners, winner;
winner <span class="Keyword">=</span> arguments[<span class="Number">0</span>], runners <span class="Keyword">=</span> <span class="Number">2</span> <span class="Keyword"><=</span> arguments.<span class="LibraryConstant">length</span> ? __slice.<span class="LibraryFunction">call</span>(arguments, <span class="Number">1</span>) : [];
<span class="Keyword">return</span> <span class="LibraryFunction">print</span>(winner, runners);
};
<span class="Keyword">if</span> (<span class="Keyword">typeof</span> elvis <span class="Keyword">!</span><span class="Keyword">=</span> <span class="String"><span class="String">"</span>undefined<span class="String">"</span></span> <span class="Keyword">&</span><span class="Keyword">&</span> elvis <span class="Keyword">!</span><span class="Keyword">==</span> <span class="BuiltInConstant">null</span>) {
<span class="LibraryFunction">alert</span>(<span class="String"><span class="String">"</span>I knew it!<span class="String">"</span></span>);
}
cubes <span class="Keyword">=</span> (<span class="Storage">function</span>() {
_results <span class="Keyword">=</span> [];
<span class="Keyword">for</span> (_i <span class="Keyword">=</span> <span class="Number">0</span>, _len <span class="Keyword">=</span> list.<span class="LibraryConstant">length</span>; _i <span class="Keyword"><</span> _len; _i<span class="Keyword">++</span>) {
num <span class="Keyword">=</span> list[_i];
_results.<span class="LibraryFunction">push</span>(math.cube(num));
}
<span class="Keyword">return</span> _results;
}());
</pre><button onclick='javascript: var cubes, list, math, num, number, opposite, race, square, _i, _len, _results;
var __slice = Array.prototype.slice;
number = 42;
opposite = true;
if (opposite) {
number = -42;
}
square = function(x) {
return x * x;
};
list = [1, 2, 3, 4, 5];
math = {
root: Math.sqrt,
square: square,
cube: function(x) {
return x * square(x);
}
};
race = function() {
var runners, winner;
winner = arguments[0], runners = 2 <= arguments.length ? __slice.call(arguments, 1) : [];
return print(winner, runners);
};
if (typeof elvis != "undefined" && elvis !== null) {
alert("I knew it!");
}
cubes = (function() {
_results = [];
for (_i = 0, _len = list.length; _i < _len; _i++) {
num = list[_i];
_results.push(math.cube(num));
}
return _results;
}());;alert(cubes);'>run: cubes</button><br class='clear' /></div>
<h2>
<span id="installation" class="bookmark"></span>
Installation and Usage
</h2>
<p>
The CoffeeScript compiler
<a href="documentation/docs/grammar.html">is itself written in CoffeeScript</a>,
using the <a href="http://jison.org">Jison parser generator</a>. The command-line
version of <tt>coffee</tt> 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 any
JavaScript environment, or in the browser (see "Try CoffeeScript", above).
</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>, and <a href="http://npmjs.org">NPM</a>
(the Node Package Manager). You can then install CoffeeScript with NPM:
</p>
<pre>
npm install coffee-script</pre>
<p>
If you'd prefer to install the latest master version of CoffeeScript, you
can clone the CoffeeScript
<a href="http://github.com/jashkenas/coffee-script">source repository</a>
from GitHub, or download
<a href="http://github.com/jashkenas/coffee-script/tarball/master">the source</a> directly.
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>
Both of these provide the <tt>coffee</tt> command, which can execute
coffee scripts, compile <tt>.coffee</tt> files into <tt>.js</tt>, and
provides an interactive REPL. The <tt>coffee</tt> command takes 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 <br /> <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>-r, --require</code></td>
<td>
Load a library before compiling or executing your script. Can be used
to hook in to the compiler (to add Growl notifications, for example).
</td>
</tr>
<tr>
<td><code>-b, --bare</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 -o lib/ -c src/
coffee --watch --lint experimental.coffee
coffee --print app/scripts/*.coffee > concatenation.js
coffee --bare --print --stdio</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>. The implicit call wraps forward
to the end of the line or block expression.
</p>
<p>
Within object literals, indentation can be used to create nested objects.
</p>
<p>
<span id="functions" class="bookmark"></span>
<b class="header">Functions</b>
Functions are defined by a list of parameters, an arrow, and the
function body. The empty function looks like this: <tt>-></tt>
</p>
<div class='code'><pre class="idle"><span class="FunctionName">square </span><span class="Keyword">=</span> <span class="FunctionArgument">(x)</span> <span class="Storage">-></span> x <span class="Keyword">*</span> x
<span class="FunctionName">cube </span><span class="Keyword">=</span> <span class="FunctionArgument">(x)</span> <span class="Storage">-></span> square(x) <span class="Keyword">*</span> x
</pre><pre class="idle"><span class="Storage">var</span> cube, square;
<span class="FunctionName">square</span> = <span class="Storage">function</span>(<span class="FunctionArgument">x</span>) {
<span class="Keyword">return</span> x <span class="Keyword">*</span> x;
};
<span class="FunctionName">cube</span> = <span class="Storage">function</span>(<span class="FunctionArgument">x</span>) {
<span class="Keyword">return</span> square(x) <span class="Keyword">*</span> x;
};
</pre><button onclick='javascript: var cube, square;
square = function(x) {
return x * x;
};
cube = function(x) {
return square(x) * x;
};;alert(cube(5));'>run: cube(5)</button><br class='clear' /></div>
<p>
Functions may also have default values for arguments.
</p>
<div class='code'><pre class="idle"><span class="FunctionName">fill </span><span class="Keyword">=</span> <span class="FunctionArgument">(container, liquid = "coffee")</span> <span class="Storage">-></span>
<span class="String"><span class="String">"</span>Filling the <span class="String"><span class="String">#{</span>container<span class="String">}</span></span> with <span class="String"><span class="String">#{</span>liquid<span class="String">}</span></span>...<span class="String">"</span></span>
</pre><pre class="idle"><span class="Storage">var</span> fill;
<span class="FunctionName">fill</span> = <span class="Storage">function</span>(<span class="FunctionArgument">container, liquid</span>) {
<span class="Keyword">if</span> (liquid <span class="Keyword">==</span> <span class="BuiltInConstant">null</span>) {
liquid <span class="Keyword">=</span> <span class="String"><span class="String">"</span>coffee<span class="String">"</span></span>;
}
<span class="Keyword">return</span> <span class="String"><span class="String">"</span>Filling the <span class="String">"</span></span> <span class="Keyword">+</span> container <span class="Keyword">+</span> <span class="String"><span class="String">"</span> with <span class="String">"</span></span> <span class="Keyword">+</span> liquid <span class="Keyword">+</span> <span class="String"><span class="String">"</span>...<span class="String">"</span></span>;
};
</pre><button onclick='javascript: var fill;
fill = function(container, liquid) {
if (liquid == null) {
liquid = "coffee";
}
return "Filling the " + container + " with " + liquid + "...";
};;alert(fill("cup"));'>run: fill("cup")</button><br class='clear' /></div>
<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 each property is listed on its own line, the commas are
optional. Objects may be created using indentation instead of
explicit braces, similar to YAML.
</p>
<div class='code'><pre class="idle">song <span class="Keyword">=</span> [<span class="String"><span class="String">"</span>do<span class="String">"</span></span>, <span class="String"><span class="String">"</span>re<span class="String">"</span></span>, <span class="String"><span class="String">"</span>mi<span class="String">"</span></span>, <span class="String"><span class="String">"</span>fa<span class="String">"</span></span>, <span class="String"><span class="String">"</span>so<span class="String">"</span></span>]
singers <span class="Keyword">=</span> {Jagger: <span class="String"><span class="String">"</span>Rock<span class="String">"</span></span>, Elvis: <span class="String"><span class="String">"</span>Roll<span class="String">"</span></span>}
matrix <span class="Keyword">=</span> [
<span class="Number">1</span>, <span class="Number">0</span>, <span class="Number">1</span>
<span class="Number">0</span>, <span class="Number">0</span>, <span class="Number">1</span>
<span class="Number">1</span>, <span class="Number">1</span>, <span class="Number">0</span>
]
kids <span class="Keyword">=</span>
brother:
name: <span class="String"><span class="String">"</span>Max<span class="String">"</span></span>
age: <span class="Number">11</span>
sister:
name: <span class="String"><span class="String">"</span>Ida<span class="String">"</span></span>
age: <span class="Number">9</span>
</pre><pre class="idle"><span class="Storage">var</span> kids, matrix, singers, song;
song <span class="Keyword">=</span> [<span class="String"><span class="String">"</span>do<span class="String">"</span></span>, <span class="String"><span class="String">"</span>re<span class="String">"</span></span>, <span class="String"><span class="String">"</span>mi<span class="String">"</span></span>, <span class="String"><span class="String">"</span>fa<span class="String">"</span></span>, <span class="String"><span class="String">"</span>so<span class="String">"</span></span>];
singers <span class="Keyword">=</span> {
Jagger: <span class="String"><span class="String">"</span>Rock<span class="String">"</span></span>,
Elvis: <span class="String"><span class="String">"</span>Roll<span class="String">"</span></span>
};
matrix <span class="Keyword">=</span> [<span class="Number">1</span>, <span class="Number">0</span>, <span class="Number">1</span>, <span class="Number">0</span>, <span class="Number">0</span>, <span class="Number">1</span>, <span class="Number">1</span>, <span class="Number">1</span>, <span class="Number">0</span>];
kids <span class="Keyword">=</span> {
brother: {
name: <span class="String"><span class="String">"</span>Max<span class="String">"</span></span>,
age: <span class="Number">11</span>
},
sister: {
name: <span class="String"><span class="String">"</span>Ida<span class="String">"</span></span>,
age: <span class="Number">9</span>
}
};
</pre><button onclick='javascript: var kids, matrix, singers, song;
song = ["do", "re", "mi", "fa", "so"];
singers = {
Jagger: "Rock",
Elvis: "Roll"
};
matrix = [1, 0, 1, 0, 0, 1, 1, 1, 0];
kids = {
brother: {
name: "Max",
age: 11
},
sister: {
name: "Ida",
age: 9
}
};;alert(song.join(","));'>run: song.join(",")</button><br class='clear' /></div>
<p>
In JavaScript, you can't use reserved words, like <tt>class</tt>, as properties
of an object, without quoting them as strings. CoffeeScript notices reserved words
used as keys in objects and quotes them for you, so you don't have to worry
about it (say, when using jQuery).
</p>
<div class='code'><pre class="idle">$(<span class="String"><span class="String">'</span>.account<span class="String">'</span></span>).attr class: <span class="String"><span class="String">'</span>active<span class="String">'</span></span>
log object.class
</pre><pre class="idle"><span class="Keyword">$</span>(<span class="String"><span class="String">'</span>.account<span class="String">'</span></span>).attr({
<span class="String"><span class="String">"</span>class<span class="String">"</span></span>: <span class="String"><span class="String">'</span>active<span class="String">'</span></span>
});
<span class="LibraryFunction">log</span>(object[<span class="String"><span class="String">"</span>class<span class="String">"</span></span>]);
</pre><br class='clear' /></div>
<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>
<div class='code'><pre class="idle">outer <span class="Keyword">=</span> <span class="Number">1</span>
<span class="FunctionName">changeNumbers </span><span class="Keyword">=</span> <span class="Keyword">-</span><span class="Keyword">></span>
inner <span class="Keyword">=</span> <span class="Keyword">-</span><span class="Number">1</span>
outer <span class="Keyword">=</span> <span class="Number">10</span>
inner <span class="Keyword">=</span> changeNumbers()
</pre><pre class="idle"><span class="Storage">var</span> changeNumbers, inner, outer;
outer <span class="Keyword">=</span> <span class="Number">1</span>;
<span class="FunctionName">changeNumbers</span> = <span class="Storage">function</span>() {
<span class="Storage">var</span> inner;
inner <span class="Keyword">=</span> <span class="Keyword">-</span><span class="Number">1</span>;
<span class="Keyword">return</span> outer <span class="Keyword">=</span> <span class="Number">10</span>;
};
inner <span class="Keyword">=</span> changeNumbers();
</pre><button onclick='javascript: var changeNumbers, inner, outer;
outer = 1;
changeNumbers = function() {
var inner;
inner = -1;
return outer = 10;
};
inner = changeNumbers();;alert(inner);'>run: inner</button><br class='clear' /></div>
<p>
Notice how all of the variable declarations have been pushed up to
the top of the closest scope, the first time they appear.
<b>outer</b> is not redeclared within the inner function, because it's
already in scope; <b>inner</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> (covered below), gives you a
reliable way to figure out where to add them, if you're targeting both
CommonJS and the browser: <tt>exports ? this</tt>
</p>
<p>
<span id="conditionals" class="bookmark"></span>
<b class="header">If, Else, Unless, 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 can compile <b>if</b> statements into JavaScript expressions,
using the ternary operator when possible, and closure wrapping otherwise. There
is no explicit ternary statement in CoffeeScript — you simply use
a regular <b>if</b> statement on a single line.
</p>
<div class='code'><pre class="idle">mood <span class="Keyword">=</span> greatlyImproved <span class="Keyword">if</span> singing
<span class="Keyword">if</span> happy <span class="Keyword">and</span> knowsIt
clapsHands()
chaChaCha()
<span class="Keyword">else</span>
showIt()
date <span class="Keyword">=</span> <span class="Keyword">if</span> friday <span class="Keyword">then</span> sue <span class="Keyword">else</span> jill
options <span class="Keyword">or=</span> defaults
</pre><pre class="idle"><span class="Storage">var</span> date, mood;
<span class="Keyword">if</span> (singing) {
mood <span class="Keyword">=</span> greatlyImproved;
}
<span class="Keyword">if</span> (happy <span class="Keyword">&</span><span class="Keyword">&</span> knowsIt) {
clapsHands();
chaChaCha();
} <span class="Keyword">else</span> {
showIt();
}
date <span class="Keyword">=</span> friday ? sue : jill;
options <span class="Keyword">||</span> (options <span class="Keyword">=</span> defaults);
</pre><br class='clear' /></div>
<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>
<p>
You can use <tt>in</tt> to test for array presence, and <tt>of</tt> to
test for JavaScript object-key presence.
</p>
<p>
All together now:
</p>
<table class="definitions">
<tr><th>CoffeeScript</th><th>JavaScript</th></tr>
<tr><td><tt>is</tt></td><td><tt>===</tt></td></tr>
<tr><td><tt>isnt</tt></td><td><tt>!==</tt></td></tr>
<tr><td><tt>not</tt></td><td><tt>!</tt></td></tr>
<tr><td><tt>and</tt></td><td><tt>&&</tt></td></tr>
<tr><td><tt>or</tt></td><td><tt>||</tt></td></tr>
<tr><td><tt>true, yes, on</tt></td><td><tt>true</tt></td></tr>
<tr><td><tt>false, no, off</tt></td><td><tt>false</tt></td></tr>
<tr><td><tt>@, this</tt></td><td><tt>this</tt></td></tr>
<tr><td><tt>of</tt></td><td><tt>in</tt></td></tr>
<tr><td><tt>in</tt></td><td>(no JS equivalent)</td></tr>
</table>
<div class='code'><pre class="idle">launch() <span class="Keyword">if</span> ignition <span class="Keyword">is</span> <span class="BuiltInConstant">on</span>
volume <span class="Keyword">=</span> <span class="Number">10</span> <span class="Keyword">if</span> band <span class="Keyword">isnt</span> SpinalTap
letTheWildRumpusBegin() <span class="Keyword">unless</span> answer <span class="Keyword">is</span> <span class="BuiltInConstant">no</span>
<span class="Keyword">if</span> car.speed <span class="Keyword"><</span> limit <span class="Keyword">then</span> accelerate()
winner <span class="Keyword">=</span> <span class="BuiltInConstant">yes</span> <span class="Keyword">if</span> pick <span class="Keyword">in</span> [<span class="Number">47</span>, <span class="Number">92</span>, <span class="Number">13</span>]
print inspect <span class="String"><span class="String">"</span>My name is <span class="String">"</span></span> <span class="Keyword">+</span> <span class="Variable">@name</span>
</pre><pre class="idle"><span class="Storage">var</span> volume, winner;
<span class="Keyword">if</span> (ignition <span class="Keyword">===</span> <span class="BuiltInConstant">true</span>) {
launch();
}
<span class="Keyword">if</span> (band <span class="Keyword">!</span><span class="Keyword">==</span> SpinalTap) {
volume <span class="Keyword">=</span> <span class="Number">10</span>;
}
<span class="Keyword">if</span> (answer <span class="Keyword">!</span><span class="Keyword">==</span> <span class="BuiltInConstant">false</span>) {
letTheWildRumpusBegin();
}
<span class="Keyword">if</span> (car.speed <span class="Keyword"><</span> limit) {
accelerate();
}
<span class="Keyword">if</span> (pick <span class="Keyword">===</span> <span class="Number">47</span> <span class="Keyword">||</span> pick <span class="Keyword">===</span> <span class="Number">92</span> <span class="Keyword">||</span> pick <span class="Keyword">===</span> <span class="Number">13</span>) {
winner <span class="Keyword">=</span> <span class="BuiltInConstant">true</span>;
}
<span class="LibraryFunction">print</span>(inspect(<span class="String"><span class="String">"</span>My name is <span class="String">"</span></span> <span class="Keyword">+</span> <span class="Variable">this</span>.<span class="LibraryConstant">name</span>));
</pre><br class='clear' /></div>
<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>
<div class='code'><pre class="idle">gold <span class="Keyword">=</span> silver <span class="Keyword">=</span> rest <span class="Keyword">=</span> <span class="String"><span class="String">"</span>unknown<span class="String">"</span></span>
<span class="FunctionName">awardMedals </span><span class="Keyword">=</span> <span class="FunctionArgument">(first, second, others...)</span> <span class="Storage">-></span>
gold <span class="Keyword">=</span> first
silver <span class="Keyword">=</span> second
rest <span class="Keyword">=</span> others
contenders <span class="Keyword">=</span> [
<span class="String"><span class="String">"</span>Michael Phelps<span class="String">"</span></span>
<span class="String"><span class="String">"</span>Liu Xiang<span class="String">"</span></span>
<span class="String"><span class="String">"</span>Yao Ming<span class="String">"</span></span>
<span class="String"><span class="String">"</span>Allyson Felix<span class="String">"</span></span>
<span class="String"><span class="String">"</span>Shawn Johnson<span class="String">"</span></span>
<span class="String"><span class="String">"</span>Roman Sebrle<span class="String">"</span></span>
<span class="String"><span class="String">"</span>Guo Jingjing<span class="String">"</span></span>
<span class="String"><span class="String">"</span>Tyson Gay<span class="String">"</span></span>
<span class="String"><span class="String">"</span>Asafa Powell<span class="String">"</span></span>
<span class="String"><span class="String">"</span>Usain Bolt<span class="String">"</span></span>
]
awardMedals contenders...
alert <span class="String"><span class="String">"</span>Gold: <span class="String">"</span></span> <span class="Keyword">+</span> gold
alert <span class="String"><span class="String">"</span>Silver: <span class="String">"</span></span> <span class="Keyword">+</span> silver
alert <span class="String"><span class="String">"</span>The Field: <span class="String">"</span></span> <span class="Keyword">+</span> rest
</pre><pre class="idle"><span class="Storage">var</span> awardMedals, contenders, gold, rest, silver;
<span class="Storage">var</span> __slice <span class="Keyword">=</span> <span class="LibraryClassType">Array</span>.<span class="LibraryConstant">prototype</span>.slice;
gold <span class="Keyword">=</span> silver <span class="Keyword">=</span> rest <span class="Keyword">=</span> <span class="String"><span class="String">"</span>unknown<span class="String">"</span></span>;
<span class="FunctionName">awardMedals</span> = <span class="Storage">function</span>() {
<span class="Storage">var</span> first, others, second;
first <span class="Keyword">=</span> arguments[<span class="Number">0</span>], second <span class="Keyword">=</span> arguments[<span class="Number">1</span>], others <span class="Keyword">=</span> <span class="Number">3</span> <span class="Keyword"><=</span> arguments.<span class="LibraryConstant">length</span> ? __slice.<span class="LibraryFunction">call</span>(arguments, <span class="Number">2</span>) : [];
gold <span class="Keyword">=</span> first;
silver <span class="Keyword">=</span> second;
<span class="Keyword">return</span> rest <span class="Keyword">=</span> others;
};
contenders <span class="Keyword">=</span> [<span class="String"><span class="String">"</span>Michael Phelps<span class="String">"</span></span>, <span class="String"><span class="String">"</span>Liu Xiang<span class="String">"</span></span>, <span class="String"><span class="String">"</span>Yao Ming<span class="String">"</span></span>, <span class="String"><span class="String">"</span>Allyson Felix<span class="String">"</span></span>, <span class="String"><span class="String">"</span>Shawn Johnson<span class="String">"</span></span>, <span class="String"><span class="String">"</span>Roman Sebrle<span class="String">"</span></span>, <span class="String"><span class="String">"</span>Guo Jingjing<span class="String">"</span></span>, <span class="String"><span class="String">"</span>Tyson Gay<span class="String">"</span></span>, <span class="String"><span class="String">"</span>Asafa Powell<span class="String">"</span></span>, <span class="String"><span class="String">"</span>Usain Bolt<span class="String">"</span></span>];
awardMedals.<span class="LibraryFunction">apply</span>(<span class="BuiltInConstant">null</span>, contenders);
<span class="LibraryFunction">alert</span>(<span class="String"><span class="String">"</span>Gold: <span class="String">"</span></span> <span class="Keyword">+</span> gold);
<span class="LibraryFunction">alert</span>(<span class="String"><span class="String">"</span>Silver: <span class="String">"</span></span> <span class="Keyword">+</span> silver);
<span class="LibraryFunction">alert</span>(<span class="String"><span class="String">"</span>The Field: <span class="String">"</span></span> <span class="Keyword">+</span> rest);
</pre><button onclick='javascript: var awardMedals, contenders, gold, rest, silver;
var __slice = Array.prototype.slice;
gold = silver = rest = "unknown";
awardMedals = function() {
var first, others, second;
first = arguments[0], second = arguments[1], others = 3 <= arguments.length ? __slice.call(arguments, 2) : [];
gold = first;
silver = second;
return rest = others;
};
contenders = ["Michael Phelps", "Liu Xiang", "Yao Ming", "Allyson Felix", "Shawn Johnson", "Roman Sebrle", "Guo Jingjing", "Tyson Gay", "Asafa Powell", "Usain Bolt"];
awardMedals.apply(null, contenders);
alert("Gold: " + gold);
alert("Silver: " + silver);
alert("The Field: " + rest);;'>run</button><br class='clear' /></div>
<p>
<span id="while" class="bookmark"></span>
<b class="header">While, Until, and Loop</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>
<div class='code'><pre class="idle"><span class="Comment"><span class="Comment">#</span> Econ 101</span>
<span class="Keyword">if</span> <span class="Variable">this</span>.studyingEconomics
buy() <span class="Keyword">while</span> supply <span class="Keyword">></span> demand
sell() <span class="Keyword">until</span> supply <span class="Keyword">></span> demand
<span class="Comment"><span class="Comment">#</span> Nursery Rhyme</span>
num <span class="Keyword">=</span> <span class="Number">6</span>
lyrics <span class="Keyword">=</span> <span class="Keyword">while</span> num <span class="Keyword">-</span><span class="Keyword">=</span> <span class="Number">1</span>
num <span class="Keyword">+</span> <span class="String"><span class="String">"</span> little monkeys, jumping on the bed.</span>
<span class="String"> One fell out and bumped his head.<span class="String">"</span></span>
</pre><pre class="idle"><span class="Storage">var</span> lyrics, num, _results;
<span class="Keyword">if</span> (<span class="Variable">this</span>.studyingEconomics) {
<span class="Keyword">while</span> (supply <span class="Keyword">></span> demand) {
buy();
}
<span class="Keyword">while</span> (<span class="Keyword">!</span>(supply <span class="Keyword">></span> demand)) {
sell();
}
}
num <span class="Keyword">=</span> <span class="Number">6</span>;
<span class="FunctionName">lyrics</span> = <span class="Storage">function</span>() {
_results <span class="Keyword">=</span> [];
<span class="Keyword">while</span> (num <span class="Keyword">-</span><span class="Keyword">=</span> <span class="Number">1</span>) {
_results.<span class="LibraryFunction">push</span>(num <span class="Keyword">+</span> <span class="String"><span class="String">"</span> little monkeys, jumping on the bed. One fell out and bumped his head.<span class="String">"</span></span>);
}
<span class="Keyword">return</span> _results;
}();
</pre><button onclick='javascript: var lyrics, num, _results;
if (this.studyingEconomics) {
while (supply > demand) {
buy();
}
while (!(supply > demand)) {
sell();
}
}
num = 6;
lyrics = function() {
_results = [];
while (num -= 1) {
_results.push(num + " little monkeys, jumping on the bed. One fell out and bumped his head.");
}
return _results;
}();;alert(lyrics.join("\n"));'>run: lyrics.join("\n")</button><br class='clear' /></div>
<p>
For readability, the <b>until</b> keyword is equivalent to <tt>while not</tt>,
and the <b>loop</b> keyword is equivalent to <tt>while true</tt>.
Other JavaScript loops, such as <b>for</b> loops and <b>do-while</b> loops
can be mimicked by variations on <b>loop</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>
<div class='code'><pre class="idle"><span class="Comment"><span class="Comment">#</span> Eat lunch.</span>
eat food <span class="Keyword">for</span> food <span class="Keyword">in</span> [<span class="String"><span class="String">'</span>toast<span class="String">'</span></span>, <span class="String"><span class="String">'</span>cheese<span class="String">'</span></span>, <span class="String"><span class="String">'</span>wine<span class="String">'</span></span>]
</pre><pre class="idle"><span class="Storage">var</span> food, _i, _len, _ref;
_ref <span class="Keyword">=</span> [<span class="String"><span class="String">'</span>toast<span class="String">'</span></span>, <span class="String"><span class="String">'</span>cheese<span class="String">'</span></span>, <span class="String"><span class="String">'</span>wine<span class="String">'</span></span>];
<span class="Keyword">for</span> (_i <span class="Keyword">=</span> <span class="Number">0</span>, _len <span class="Keyword">=</span> _ref.<span class="LibraryConstant">length</span>; _i <span class="Keyword"><</span> _len; _i<span class="Keyword">++</span>) {
food <span class="Keyword">=</span> _ref[_i];
eat(food);
}
</pre><br class='clear' /></div>
<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.
</p>
<div class='code'><pre class="idle">countdown <span class="Keyword">=</span> (num <span class="Keyword">for</span> num <span class="Keyword">in</span> [<span class="Number">10</span>..<span class="Number">1</span>])
</pre><pre class="idle"><span class="Storage">var</span> countdown, num, _results;
countdown <span class="Keyword">=</span> (<span class="Storage">function</span>() {
_results <span class="Keyword">=</span> [];
<span class="Keyword">for</span> (num <span class="Keyword">=</span> <span class="Number">10</span>; num <span class="Keyword">>=</span> <span class="Number">1</span>; num<span class="Keyword">--</span>) {
_results.<span class="LibraryFunction">push</span>(num);
}
<span class="Keyword">return</span> _results;
}());
</pre><button onclick='javascript: var countdown, num, _results;
countdown = (function() {
_results = [];
for (num = 10; num >= 1; num--) {
_results.push(num);
}
return _results;
}());;alert(countdown);'>run: countdown</button><br class='clear' /></div>
<p>
Note how because we are assigning the value of the comprehensions to a
variable in the example above, CoffeeScript is collecting the result of
each iteration into an array. Sometimes functions end with loops that are
intended to run only for their side-effects. Be careful that you're not
accidentally returning the results of the comprehension in these cases,
by adding a meaningful return value, like <tt>true</tt>, or <tt>null</tt>,
to the bottom of your function.
</p>
<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>
<div class='code'><pre class="idle">yearsOld <span class="Keyword">=</span> max: <span class="Number">10</span>, ida: <span class="Number">9</span>, tim: <span class="Number">11</span>
ages <span class="Keyword">=</span> <span class="Keyword">for</span> child, age <span class="Keyword">of</span> yearsOld
child <span class="Keyword">+</span> <span class="String"><span class="String">"</span> is <span class="String">"</span></span> <span class="Keyword">+</span> age
</pre><pre class="idle"><span class="Storage">var</span> age, ages, child, yearsOld, _results;
yearsOld <span class="Keyword">=</span> {
max: <span class="Number">10</span>,
ida: <span class="Number">9</span>,
tim: <span class="Number">11</span>
};
<span class="FunctionName">ages</span> = <span class="Storage">function</span>() {
_results <span class="Keyword">=</span> [];
<span class="Keyword">for</span> (child <span class="Keyword">in</span> yearsOld) {
age <span class="Keyword">=</span> yearsOld[child];
_results.<span class="LibraryFunction">push</span>(child <span class="Keyword">+</span> <span class="String"><span class="String">"</span> is <span class="String">"</span></span> <span class="Keyword">+</span> age);
}
<span class="Keyword">return</span> _results;
}();
</pre><button onclick='javascript: var age, ages, child, yearsOld, _results;
yearsOld = {
max: 10,
ida: 9,
tim: 11
};
ages = function() {
_results = [];
for (child in yearsOld) {
age = yearsOld[child];
_results.push(child + " is " + age);
}
return _results;
}();;alert(ages.join(", "));'>run: ages.join(", ")</button><br class='clear' /></div>
<p>
By default, object comprehensions are safe, and use a <tt>hasOwnProperty</tt>
check to make sure that you're dealing with properties on the current
object. If you'd like the regular JavaScript <br /><tt>for (key in obj) ...</tt>
loop, for speed or for another reason, you can use <br />
<tt>for all key, value of object</tt> in CoffeeScript.
</p>
<p>
<span id="slices" class="bookmark"></span>
<b class="header">Array Slicing and Splicing with Ranges</b>
Ranges can also be used to extract slices of arrays.
With two dots (<tt>3..6</tt>), the range is inclusive (<tt>3, 4, 5, 6</tt>);
with three docs (<tt>3...6</tt>), the range excludes the end (<tt>3, 4, 5</tt>).
</p>
<div class='code'><pre class="idle">numbers <span class="Keyword">=</span> [<span class="Number">0</span>, <span class="Number">1</span>, <span class="Number">2</span>, <span class="Number">3</span>, <span class="Number">4</span>, <span class="Number">5</span>, <span class="Number">6</span>, <span class="Number">7</span>, <span class="Number">8</span>, <span class="Number">9</span>]
copy <span class="Keyword">=</span> numbers[<span class="Number">0</span>...numbers.length]
middle <span class="Keyword">=</span> copy[<span class="Number">3</span>..<span class="Number">6</span>]
</pre><pre class="idle"><span class="Storage">var</span> copy, middle, numbers;
numbers <span class="Keyword">=</span> [<span class="Number">0</span>, <span class="Number">1</span>, <span class="Number">2</span>, <span class="Number">3</span>, <span class="Number">4</span>, <span class="Number">5</span>, <span class="Number">6</span>, <span class="Number">7</span>, <span class="Number">8</span>, <span class="Number">9</span>];
copy <span class="Keyword">=</span> numbers.<span class="LibraryFunction">slice</span>(<span class="Number">0</span>, numbers.<span class="LibraryConstant">length</span>);
middle <span class="Keyword">=</span> copy.<span class="LibraryFunction">slice</span>(<span class="Number">3</span>, <span class="Number">6</span> <span class="Keyword">+</span> <span class="Number">1</span>);
</pre><button onclick='javascript: var copy, middle, numbers;
numbers = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9];
copy = numbers.slice(0, numbers.length);
middle = copy.slice(3, 6 + 1);;alert(middle);'>run: middle</button><br class='clear' /></div>
<p>
The same syntax can be used with assignment to replace a segment of an array
with new values, splicing it.
</p>
<div class='code'><pre class="idle">numbers <span class="Keyword">=</span> [<span class="Number">0</span>, <span class="Number">1</span>, <span class="Number">2</span>, <span class="Number">3</span>, <span class="Number">4</span>, <span class="Number">5</span>, <span class="Number">6</span>, <span class="Number">7</span>, <span class="Number">8</span>, <span class="Number">9</span>]
numbers[<span class="Number">3</span>..<span class="Number">6</span>] <span class="Keyword">=</span> [<span class="Keyword">-</span><span class="Number">3</span>, <span class="Keyword">-</span><span class="Number">4</span>, <span class="Keyword">-</span><span class="Number">5</span>, <span class="Keyword">-</span><span class="Number">6</span>]
</pre><pre class="idle"><span class="Storage">var</span> numbers;
numbers <span class="Keyword">=</span> [<span class="Number">0</span>, <span class="Number">1</span>, <span class="Number">2</span>, <span class="Number">3</span>, <span class="Number">4</span>, <span class="Number">5</span>, <span class="Number">6</span>, <span class="Number">7</span>, <span class="Number">8</span>, <span class="Number">9</span>];
[].splice.<span class="LibraryFunction">apply</span>(numbers, [<span class="Number">3</span>, <span class="Number">4</span>].<span class="LibraryFunction">concat</span>([<span class="Keyword">-</span><span class="Number">3</span>, <span class="Keyword">-</span><span class="Number">4</span>, <span class="Keyword">-</span><span class="Number">5</span>, <span class="Keyword">-</span><span class="Number">6</span>]));
</pre><button onclick='javascript: var numbers;
numbers = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9];
[].splice.apply(numbers, [3, 4].concat([-3, -4, -5, -6]));;alert(numbers);'>run: numbers</button><br class='clear' /></div>
<p>
Note that JavaScript strings are immutable, and can't be spliced.
</p>
<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>
<div class='code'><pre class="idle"><span class="FunctionName">grade </span><span class="Keyword">=</span> <span class="FunctionArgument">(student)</span> <span class="Storage">-></span>
<span class="Keyword">if</span> student.excellentWork
<span class="String"><span class="String">"</span>A+<span class="String">"</span></span>
<span class="Keyword">else</span> <span class="Keyword">if</span> student.okayStuff
<span class="Keyword">if</span> student.triedHard <span class="Keyword">then</span> <span class="String"><span class="String">"</span>B<span class="String">"</span></span> <span class="Keyword">else</span> <span class="String"><span class="String">"</span>B-<span class="String">"</span></span>
<span class="Keyword">else</span>
<span class="String"><span class="String">"</span>C<span class="String">"</span></span>
eldest <span class="Keyword">=</span> <span class="Keyword">if</span> <span class="Number">24</span> <span class="Keyword">></span> <span class="Number">21</span> <span class="Keyword">then</span> <span class="String"><span class="String">"</span>Liz<span class="String">"</span></span> <span class="Keyword">else</span> <span class="String"><span class="String">"</span>Ike<span class="String">"</span></span>
</pre><pre class="idle"><span class="Storage">var</span> eldest, grade;
<span class="FunctionName">grade</span> = <span class="Storage">function</span>(<span class="FunctionArgument">student</span>) {