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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>
<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 menu">
<a href="#overview">Overview</a>
<a href="#installation">Installation and Usage</a>
<a href="#language">Language Reference</a>
<a href="#literals">Literals: Functions, 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="#splats">Splats...</a>
<a href="#loops">Loops and Comprehensions</a>
<a href="#slices">Array Slicing and Splicing</a>
<a href="#expressions">Everything is an Expression</a>
<a href="#operators">Operators and Aliases</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 and Try/Catch</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="#resources">Examples and Resources</a>
<a href="#change_log">Change Log</a>
</div>
</div>
<div class="navigation try">
<div class="button">
Try CoffeeScript
<div class="repl_bridge"></div>
</div>
<div class="contents repl_wrapper">
<div class="code">
<div class="screenshadow tl"></div>
<div class="screenshadow tr"></div>
<div class="screenshadow bl"></div>
<div class="screenshadow br"></div>
<div id="repl_source_wrap">
<textarea id="repl_source" rows="100">alert "Hello CoffeeScript!"</textarea>
</div>
<pre id="repl_results"></pre>
<div class="minibutton dark run">Run</div>
<br class="clear" />
</div>
</div>
</div>
<div class="navigation annotated">
<div class="button">
Annotated Source
</div>
<div class="contents menu">
<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>
<b>CoffeeScript is a little language that compiles into JavaScript.</b> 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, will work in every JavaScript implementation, and tends
to run as fast or faster than the equivalent handwritten JavaScript.
</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;
<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>() {
<span class="Storage">var</span> _i, _len, _results;
_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><script>window.example1 = "# Assignment:\nnumber = 42\nopposite = true\n\n# Conditions:\nnumber = -42 if opposite\n\n# Functions:\nsquare = (x) -> x * x\n\n# Arrays:\nlist = [1, 2, 3, 4, 5]\n\n# Objects:\nmath =\n root: Math.sqrt\n square: square\n cube: (x) -> x * square x\n\n# Splats:\nrace = (winner, runners...) ->\n print winner, runners\n\n# Existence:\nalert \"I knew it!\" if elvis?\n\n# Array comprehensions:\ncubes = (math.cube num for num in list)\n\nalert cubes"</script><div class='minibutton ok' onclick='javascript: var cubes, list, math, num, number, opposite, race, square;
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() {
var _i, _len, _results;
_results = [];
for (_i = 0, _len = list.length; _i < _len; _i++) {
num = list[_i];
_results.push(math.cube(num));
}
return _results;
})();;alert(cubes);'>run: cubes</div><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 stable 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>
If installing on Ubuntu or Debian,
<a href="http://opinionated-programmer.com/2010/12/installing-coffeescript-on-debian-or-ubuntu/">be
careful not to use the existing out-of-date package</a>. If installing on
Windows, your best bet is probably to run Node.js under Cygwin.
</p>
<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>-j, --join</code></td>
<td>
Before compiling, concatenate all scripts together in the order they
were passed. Useful for building large projects.
</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>
<tr>
<td><code>--nodejs</code></td>
<td>
The <tt>node</tt> executable has some useful options you can set,
such as <tt>--debug</tt> and <tt>--max-stack-size</tt>. Use this
flag to forward options directly to Node.js.
</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>
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="literals" 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><script>window.example2 = "square = (x) -> x * x\ncube = (x) -> square(x) * x\n\nalert cube(5)"</script><div class='minibutton load' onclick='javascript: loadConsole(example2);'>Load</div><div class='minibutton ok' onclick='javascript: var cube, square;
square = function(x) {
return x * x;
};
cube = function(x) {
return square(x) * x;
};;alert(cube(5));'>run: cube(5)</div><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><script>window.example3 = "fill = (container, liquid = \"coffee\") ->\n \"Filling the #{container} with #{liquid}...\"\n\nalert fill(\"cup\")"</script><div class='minibutton load' onclick='javascript: loadConsole(example3);'>Load</div><div class='minibutton ok' 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")</div><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><script>window.example4 = "song = [\"do\", \"re\", \"mi\", \"fa\", \"so\"]\n\nsingers = {Jagger: \"Rock\", Elvis: \"Roll\"}\n\nmatrix = [\n 1, 0, 1\n 0, 0, 1\n 1, 1, 0\n]\n\nkids =\n brother:\n name: \"Max\"\n age: 11\n sister:\n name: \"Ida\"\n age: 9\n\nalert song.join(\",\")"</script><div class='minibutton load' onclick='javascript: loadConsole(example4);'>Load</div><div class='minibutton ok' 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(",")</div><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">$(<span class="String"><span class="String">'</span>.account<span class="String">'</span></span>).attr class: <span class="String"><span class="String">'</span>active<span class="String">'</span></span>
log object.<span class="Storage">class</span>
</pre><pre class="idle"><span class="Keyword">$</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><script>window.example5 = "$('.account').attr class: 'active'\n\nlog object.class\n\n\n"</script><div class='minibutton load' onclick='javascript: loadConsole(example5);'>Load</div><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><script>window.example6 = "outer = 1\nchangeNumbers = ->\n inner = -1\n outer = 10\ninner = changeNumbers()\n\nalert inner"</script><div class='minibutton load' onclick='javascript: loadConsole(example6);'>Load</div><div class='minibutton ok' onclick='javascript: var changeNumbers, inner, outer;
outer = 1;
changeNumbers = function() {
var inner;
inner = -1;
return outer = 10;
};
inner = changeNumbers();;alert(inner);'>run: inner</div><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><script>window.example7 = "mood = greatlyImproved if singing\n\nif happy and knowsIt\n clapsHands()\n chaChaCha()\nelse\n showIt()\n\ndate = if friday then sue else jill\n\noptions or= defaults\n\n\n"</script><div class='minibutton load' onclick='javascript: loadConsole(example7);'>Load</div><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><script>window.example8 = "gold = silver = rest = \"unknown\"\n\nawardMedals = (first, second, others...) ->\n gold = first\n silver = second\n rest = others\n\ncontenders = [\n \"Michael Phelps\"\n \"Liu Xiang\"\n \"Yao Ming\"\n \"Allyson Felix\"\n \"Shawn Johnson\"\n \"Roman Sebrle\"\n \"Guo Jingjing\"\n \"Tyson Gay\"\n \"Asafa Powell\"\n \"Usain Bolt\"\n]\n\nawardMedals contenders...\n\nalert \"Gold: \" + gold\nalert \"Silver: \" + silver\nalert \"The Field: \" + rest\n\n\n"</script><div class='minibutton load' onclick='javascript: loadConsole(example8);'>Load</div><div class='minibutton ok' 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</div><br class='clear' /></div>
<p>
<span id="loops" class="bookmark"></span>
<b class="header">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>
<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;
<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>;
lyrics <span class="Keyword">=</span> (<span class="Storage">function</span>() {
<span class="Storage">var</span> _results;
_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><script>window.example9 = "# Econ 101\nif this.studyingEconomics\n buy() while supply > demand\n sell() until supply > demand\n\n# Nursery Rhyme\nnum = 6\nlyrics = while num -= 1\n num + \" little monkeys, jumping on the bed.\n One fell out and bumped his head.\"\n\nalert lyrics.join(\"\\n\")"</script><div class='minibutton load' onclick='javascript: loadConsole(example9);'>Load</div><div class='minibutton ok' onclick='javascript: var lyrics, num;
if (this.studyingEconomics) {
while (supply > demand) {
buy();
}
while (!(supply > demand)) {
sell();
}
}
num = 6;
lyrics = (function() {
var _results;
_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")</div><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>.
</p>
<p>
<span id="comprehensions" class="bookmark"></span>
<b class="header">Comprehensions</b>
Hopefully, the majority of your loops can be implemented with <b>comprehensions</b>
over arrays, objects, and ranges. Comprehensions 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><script>window.example10 = "# Eat lunch.\neat food for food in ['toast', 'cheese', 'wine']\n"</script><div class='minibutton load' onclick='javascript: loadConsole(example10);'>Load</div><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;
countdown <span class="Keyword">=</span> (<span class="Storage">function</span>() {
<span class="Storage">var</span> _results;
_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><script>window.example11 = "countdown = (num for num in [10..1])\n\nalert countdown"</script><div class='minibutton load' onclick='javascript: loadConsole(example11);'>Load</div><div class='minibutton ok' onclick='javascript: var countdown, num;
countdown = (function() {
var _results;
_results = [];
for (num = 10; num >= 1; num--) {
_results.push(num);
}
return _results;
})();;alert(countdown);'>run: countdown</div><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>
To step through a range comprehension in fixed-size chunks,
use <tt>by</tt>, for example:<br />
<tt>evens = (x for x in [0..10] by 2)</tt>
</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;
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="Storage">function</span>() {
<span class="Storage">var</span> _results;
_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><script>window.example12 = "yearsOld = max: 10, ida: 9, tim: 11\n\nages = for child, age of yearsOld\n child + \" is \" + age\n\nalert ages.join(\", \")"</script><div class='minibutton load' onclick='javascript: loadConsole(example12);'>Load</div><div class='minibutton ok' onclick='javascript: var age, ages, child, yearsOld;
yearsOld = {
max: 10,
ida: 9,
tim: 11
};
ages = (function() {
var _results;
_results = [];
for (child in yearsOld) {
age = yearsOld[child];
_results.push(child + " is " + age);
}
return _results;
})();;alert(ages.join(", "));'>run: ages.join(", ")</div><br class='clear' /></div>
<p>
If you would like to iterate over just the keys that are defined on the
object itself, by adding a <tt>hasOwnProperty</tt>
check to avoid properties that may be interited from the prototype, use<br />
<tt>for own key, value of object</tt>
</p>
<p>
In JavaScript, it's extremely common to run into trouble when trying to
generate functions within a loop — all of the created functions share
the final value of loop variables. CoffeeScript provides a "scoped loop"
syntax for loops that should have function scope, similar to a <tt>forEach</tt>.
Note how the body of the loop gets lifted into a cached function.
</p>
<div class='code'><pre class="idle">funcs <span class="Keyword">=</span> []
<span class="Keyword">for</span> i <span class="Keyword">in</span> [<span class="Number">0</span>..<span class="Number">3</span>] <span class="Keyword">-</span><span class="Keyword">></span>
funcs.push <span class="FunctionArgument">(number)</span> <span class="Storage">-></span> number <span class="Keyword">+</span> i
</pre><pre class="idle"><span class="Storage">var</span> funcs, i, _fn;
funcs <span class="Keyword">=</span> [];
<span class="FunctionName">_fn</span> = <span class="Storage">function</span>(<span class="FunctionArgument">i</span>) {
funcs.<span class="LibraryFunction">push</span>(<span class="Storage">function</span>(number) {
<span class="Keyword">return</span> number <span class="Keyword">+</span> i;
});
};
<span class="Keyword">for</span> (i <span class="Keyword">=</span> <span class="Number">0</span>; i <span class="Keyword"><=</span> <span class="Number">3</span>; i<span class="Keyword">++</span>) {
_fn(i);
}
</pre><script>window.example13 = "funcs = []\n\nfor i in [0..3] ->\n funcs.push (number) -> number + i\n\nalert funcs[3](2)"</script><div class='minibutton load' onclick='javascript: loadConsole(example13);'>Load</div><div class='minibutton ok' onclick='javascript: var funcs, i, _fn;
funcs = [];
_fn = function(i) {
funcs.push(function(number) {
return number + i;
});
};
for (i = 0; i <= 3; i++) {
_fn(i);
};alert(funcs[3](2));'>run: funcs[3](2)</div><br class='clear' /></div>
<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">7</span>);
</pre><script>window.example14 = "numbers = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]\n\ncopy = numbers[0...numbers.length]\n\nmiddle = copy[3..6]\n\nalert middle"</script><div class='minibutton load' onclick='javascript: loadConsole(example14);'>Load</div><div class='minibutton ok' 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, 7);;alert(middle);'>run: middle</div><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><script>window.example15 = "numbers = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]\n\nnumbers[3..6] = [-3, -4, -5, -6]\n\nalert numbers"</script><div class='minibutton load' onclick='javascript: loadConsole(example15);'>Load</div><div class='minibutton ok' 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</div><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>) {
<span class="Keyword">if</span> (student.excellentWork) {
<span class="Keyword">return</span> <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">return</span> <span class="String"><span class="String">"</span>B<span class="String">"</span></span>;
} <span class="Keyword">else</span> {
<span class="Keyword">return</span> <span class="String"><span class="String">"</span>B-<span class="String">"</span></span>;
}
} <span class="Keyword">else</span> {
<span class="Keyword">return</span> <span class="String"><span class="String">"</span>C<span class="String">"</span></span>;
}
};
eldest <span class="Keyword">=</span> <span class="Number">24</span> <span class="Keyword">></span> <span class="Number">21</span> ? <span class="String"><span class="String">"</span>Liz<span class="String">"</span></span> : <span class="String"><span class="String">"</span>Ike<span class="String">"</span></span>;
</pre><script>window.example16 = "grade = (student) ->\n if student.excellentWork\n \"A+\"\n else if student.okayStuff\n if student.triedHard then \"B\" else \"B-\"\n else\n \"C\"\n\neldest = if 24 > 21 then \"Liz\" else \"Ike\"\n\nalert eldest"</script><div class='minibutton load' onclick='javascript: loadConsole(example16);'>Load</div><div class='minibutton ok' onclick='javascript: var eldest, grade;
grade = function(student) {
if (student.excellentWork) {
return "A+";