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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" />
</head>
<body>
<div class="container">
<h1><sub style="font-size: 100px;">☕</sub> CoffeeScript</h1>
<p>
CoffeeScript is a little language that compiles into JavaScript. Think
of it as JavaScript's less ostentatious kid brother — the same genes,
roughly the same height, but a different sense of style. Apart from a handful of
bonus goodies, statements in CoffeeScript correspond one-to-one with their
equivalent in JavaScript, it's just another way of saying it.
</p>
<p>
<b>Disclaimer:</b>
CoffeeScript is just for fun and seriously alpha. I'm sure that there are still
plenty of holes in the walls and leaks in the roof. <i>There are no guarantees
that the syntax won't change between versions.</i> That said,
it compiles into clean JavaScript (the good parts) that can use existing
JavaScript libraries seamlessly, and passes through
<a href="http://www.jslint.com/">JSLint</a> without warnings. The compiled
output is quite readable — pretty-printed, with comments
preserved intact.
</p>
<p>
<b>Latest Version:</b>
<a href="http://gemcutter.org/gems/coffee-script">0.2.6</a>
</p>
<h2>Table of Contents</h2>
<p>
<a href="#overview">Mini Overview</a><br />
<a href="#installation">Installation and Usage</a><br />
<a href="#whitespace">Significant Whitespace</a><br />
<a href="#functions">Functions and Invocation</a><br />
<a href="#assignment">Assignment</a><br />
<a href="#objects_and_arrays">Objects and Arrays</a><br />
<a href="#lexical_scope">Lexical Scoping and Variable Safety</a><br />
<a href="#conditionals">Conditionals, Ternaries, and Conditional Assignment</a><br />
<a href="#existence">The Existential Operator</a><br />
<a href="#aliases">Aliases</a><br />
<a href="#splats">Splats...</a><br />
<a href="#arguments">Arguments are Arrays</a><br />
<a href="#while">While Loops</a><br />
<a href="#comprehensions">Comprehensions (Arrays, Objects, and Ranges)</a><br />
<a href="#slice_splice">Array Slicing and Splicing with Ranges</a><br />
<a href="#expressions">Everything is an Expression</a><br />
<a href="#inheritance">Inheritance, and Calling Super from a Subclass</a><br />
<a href="#blocks">Blocks</a><br />
<a href="#pattern_matching">Pattern Matching</a><br />
<a href="#long_arrow">Function Binding</a><br />
<a href="#embedded">Embedded JavaScript</a><br />
<a href="#switch">Switch/When/Else</a><br />
<a href="#try">Try/Catch/Finally</a><br />
<a href="#comparisons">Chained Comparisons</a><br />
<a href="#strings">Multiline Strings and Heredocs</a><br />
<a href="#resources">Resources</a><br />
<a href="#contributing">Contributing</a><br />
<a href="#change_log">Change Log</a><br />
</p>
<h2 id="overview">Mini 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>
<span class="FunctionName">number</span><span class="Keyword">:</span> <span class="Number">42</span>
<span class="FunctionName">opposite_day</span><span class="Keyword">:</span> <span class="BuiltInConstant">true</span>
<span class="Comment"><span class="Comment">#</span> Conditions:</span>
<span class="FunctionName">number</span><span class="Keyword">:</span> <span class="Keyword">-</span><span class="Number">42</span> <span class="Keyword">if</span> opposite_day
<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>
<span class="FunctionName">list</span><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>
<span class="FunctionName">math</span><span class="Keyword">:</span> {
<span class="FunctionName">root</span><span class="Keyword">:</span> Math.sqrt
<span class="FunctionName">square</span><span class="Keyword">:</span> square
<span class="FunctionArgument"> cube: x </span><span class="Storage">=></span> x <span class="Keyword">*</span> square(x)
}
<span class="Comment"><span class="Comment">#</span> Splats:</span>
<span class="FunctionArgument">race: 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>
<span class="FunctionName">cubed_list</span><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> __a, __b, __c, cubed_list, list, math, num, number, opposite_day, race, square;
<span class="Comment"><span class="Comment">//</span> Assignment:</span>
number <span class="Keyword">=</span> <span class="Number">42</span>;
opposite_day <span class="Keyword">=</span> <span class="BuiltInConstant">true</span>;
<span class="Comment"><span class="Comment">//</span> Conditions:</span>
<span class="Keyword">if</span> (opposite_day) {
number <span class="Keyword">=</span> <span class="Keyword">-</span><span class="Number">42</span>;
}
<span class="Comment"><span class="Comment">//</span> Functions:</span>
square <span class="Keyword">=</span> <span class="Storage">function</span> <span class="FunctionName">square</span>(<span class="FunctionArgument">x</span>) {
<span class="Keyword">return</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: <span class="LibraryClassType">Math</span>.sqrt,
square: square,
cube: <span class="Storage">function</span> <span class="FunctionName">cube</span>(<span class="FunctionArgument">x</span>) {
<span class="Keyword">return</span> x <span class="Keyword">*</span> square(x);
}
};
<span class="Comment"><span class="Comment">//</span> Splats:</span>
race <span class="Keyword">=</span> <span class="Storage">function</span> <span class="FunctionName">race</span>(<span class="FunctionArgument">winner</span>) {
<span class="Storage">var</span> runners;
runners <span class="Keyword">=</span> <span class="LibraryClassType">Array</span>.<span class="LibraryConstant">prototype</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="Comment"><span class="Comment">//</span> Existence:</span>
<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>);
}
<span class="Comment"><span class="Comment">//</span> Array comprehensions:</span>
cubed_list <span class="Keyword">=</span> (<span class="Storage">function</span>() {
__a <span class="Keyword">=</span> []; __b <span class="Keyword">=</span> list;
<span class="Keyword">for</span> (__c <span class="Keyword">=</span> <span class="Number">0</span>; __c <span class="Keyword"><</span> __b.<span class="LibraryConstant">length</span>; __c<span class="Keyword">++</span>) {
num <span class="Keyword">=</span> __b[__c];
__a.<span class="LibraryFunction">push</span>(math.cube(num));
}
<span class="Keyword">return</span> __a;
})();
</pre><button onclick='javascript: var __a, __b, __c, cubed_list, list, math, num, number, opposite_day, race, square;
// Assignment:
number = 42;
opposite_day = true;
// Conditions:
if (opposite_day) {
number = -42;
}
// Functions:
square = function square(x) {
return x * x;
};
// Arrays:
list = [1, 2, 3, 4, 5];
// Objects:
math = {
root: Math.sqrt,
square: square,
cube: function cube(x) {
return x * square(x);
}
};
// Splats:
race = function race(winner) {
var runners;
runners = Array.prototype.slice.call(arguments, 1);
return print(winner, runners);
};
// Existence:
if ((typeof elvis !== "undefined" && elvis !== null)) {
alert("I knew it!");
}
// Array comprehensions:
cubed_list = (function() {
__a = []; __b = list;
for (__c = 0; __c < __b.length; __c++) {
num = __b[__c];
__a.push(math.cube(num));
}
return __a;
})();
;alert(cubed_list);'>run: cubed_list</button><br class='clear' /></div>
<p>
For a longer CoffeeScript example, check out
<a href="documentation/underscore.html">Underscore.coffee</a>, a port
of the <a href="http://documentcloud.github.com/underscore/">Underscore.js</a>
library of helper functions. Underscore.coffee can pass the entire Underscore.js
test suite. The CoffeeScript version is faster than the original for a number
of methods (in general, due to the speed of CoffeeScript's array comprehensions), and
after being minified and gzipped, is only 241 bytes larger than the original
JavaScript version.
Additional examples are included in the source repository, inside the
<a href="http://github.com/jashkenas/coffee-script/tree/master/examples/">examples</a> folder.
</p>
<h2 id="installation">Installation and Usage</h2>
<p>
The CoffeeScript compiler is written in pure Ruby, and is available
as a Ruby Gem.
</p>
<pre>
gem install coffee-script</pre>
<p>
Installing the gem provides the <tt>coffee</tt> command, which can
be used to compile CoffeeScript <tt>.coffee</tt> files into JavaScript, as
well as debug them. In conjunction with
<a href="http://narwhaljs.org/">Narwhal</a>, the <tt>coffee</tt>
command also provides direct evaluation and an interactive REPL.
When compiling to JavaScript, <tt>coffee</tt> writes the output
as <tt>.js</tt> files in the same directory by default, but output
can be customized with the following options:
</p>
<table>
<tr>
<td width="25%"><code>-i, --interactive</code></td>
<td>
Launch an interactive CoffeeScript session.
Requires <a href="http://narwhaljs.org/">Narwhal</a>.
</td>
</tr>
<tr>
<td><code>-r, --run</code></td>
<td>
Compile and execute scripts without saving the intermediate
JavaScript. Requires <a href="http://narwhaljs.org/">Narwhal</a>.
</td>
</tr>
<tr>
<td><code>-o, --output [DIR]</code></td>
<td>
Write out all compiled JavaScript files into the specified directory.
</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> (JavaScript Lint) command is installed, use it
to check the compilation of a CoffeeScript file. (Handy in
conjunction with <tt>--watch</tt>)
</td>
</tr>
<tr>
<td><code>-e, --eval</code></td>
<td>
Compile and print a little snippet of CoffeeScript directly from the
command line (or from <b>stdin</b>). For example:<br /><tt>coffee -e "square: x => x * x"</tt>
</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"], [":", ":"], [:PARAM, "x"]</tt> ...
</td>
</tr>
<tr>
<td><code>-v, --verbose</code></td>
<td>
As the JavaScript is being generated, print out every step of code
generation, including lexical scope and the node in the
AST.
</td>
</tr>
<tr>
<td><code>-n, --no-wrap</code></td>
<td>
Compile the JavaScript without the top-level function safety wrapper.
(Used for CoffeeScript as a Narwhal module.)
</td>
</tr>
<tr>
<td><code>-g, --globals</code></td>
<td>
Suppress all variable declarations at the top-level, effectively adding
those variables to the global scope. (Used by the REPL.)
</td>
</tr>
<tr>
<td><code>--install-bundle</code></td>
<td>
Install the TextMate bundle for CoffeeScript syntax highlighting.
</td>
</tr>
</table>
<p>
<b>Examples:</b>
</p>
<pre>
coffee path/to/script.coffee
coffee --interactive
coffee --watch --lint experimental.coffee
coffee --print app/scripts/*.coffee > concatenation.js</pre>
<h2>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 id="whitespace">
<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 can use newlines to break up your expression into smaller pieces,
as long as CoffeeScript can tell that the line hasn't finished
(similar to how Ruby handles it). For example,
if the line ends in an operator, dot, or keyword.
</p>
<p id="functions">
<b class="header">Functions and Invocation</b>
Functions are defined by a list of parameters, an arrow, and the
function body. The empty function looks like this: <tt>=></tt>. All
functions in CoffeeScript are named by default, for the benefit of debug messages.
If you'd like to create an anonymous function, just wrap it in parentheses.
</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;
square <span class="Keyword">=</span> <span class="Storage">function</span> <span class="FunctionName">square</span>(<span class="FunctionArgument">x</span>) {
<span class="Keyword">return</span> x <span class="Keyword">*</span> x;
};
cube <span class="Keyword">=</span> <span class="Storage">function</span> <span class="FunctionName">cube</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 square(x) {
return x * x;
};
cube = function cube(x) {
return square(x) * x;
};
;alert(cube(5));'>run: cube(5)</button><br class='clear' /></div>
<p id="assignment">
<b class="header">Assignment</b>
Use a colon <tt>:</tt> to assign, as in
<a href="http://json.org">JSON</a>. Equal signs are only needed for
mathy things.
</p>
<div class='code'><pre class="idle"><span class="FunctionName">greeting</span><span class="Keyword">:</span> <span class="String"><span class="String">"</span>Hello CoffeeScript<span class="String">"</span></span>
<span class="FunctionName">difficulty</span><span class="Keyword">:</span> <span class="Number">0.5</span>
</pre><pre class="idle"><span class="Storage">var</span> difficulty, greeting;
greeting <span class="Keyword">=</span> <span class="String"><span class="String">"</span>Hello CoffeeScript<span class="String">"</span></span>;
difficulty <span class="Keyword">=</span> <span class="Number">0.5</span>;
</pre><button onclick='javascript: var difficulty, greeting;
greeting = "Hello CoffeeScript";
difficulty = 0.5;
;alert(greeting);'>run: greeting</button><br class='clear' /></div>
<p>
Declarations of new variables are pushed up to the top of the nearest
lexical scope, so that assignment may always be performed within expressions.
</p>
<p id="objects_and_arrays">
<b class="header">Objects and Arrays</b>
Object and Array literals look very similar to their JavaScript cousins.
When you spread out each assignment on a separate line, the commas are
optional. In this way, assigning object properties looks the same as
assigning local variables, and can be moved around freely. You can mix
and match the two styles.
</p>
<div class='code'><pre class="idle"><span class="FunctionName">song</span><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>]
<span class="FunctionName">ages</span><span class="Keyword">:</span> {
<span class="FunctionName">max</span><span class="Keyword">:</span> <span class="Number">10</span>
<span class="FunctionName">ida</span><span class="Keyword">:</span> <span class="Number">9</span>
<span class="FunctionName">tim</span><span class="Keyword">:</span> <span class="Number">11</span>
}
<span class="FunctionName">matrix</span><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>
]
</pre><pre class="idle"><span class="Storage">var</span> ages, matrix, 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>];
ages <span class="Keyword">=</span> {
max: <span class="Number">10</span>,
ida: <span class="Number">9</span>,
tim: <span class="Number">11</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>];
</pre><button onclick='javascript: var ages, matrix, song;
song = ["do", "re", "mi", "fa", "so"];
ages = {
max: 10,
ida: 9,
tim: 11
};
matrix = [1, 0, 1, 0, 0, 1, 1, 1, 0];
;alert(song.join(","));'>run: song.join(",")</button><br class='clear' /></div>
<p id="lexical_scope">
<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"><span class="FunctionName">num</span><span class="Keyword">:</span> <span class="Number">1</span>
<span class="FunctionName">change_numbers</span><span class="Keyword">:</span> <span class="Storage">=></span>
<span class="FunctionName">new_num</span><span class="Keyword">:</span> <span class="Keyword">-</span><span class="Number">1</span>
<span class="FunctionName">num</span><span class="Keyword">:</span> <span class="Number">10</span>
<span class="FunctionName">new_num</span><span class="Keyword">:</span> change_numbers()
</pre><pre class="idle"><span class="Storage">var</span> change_numbers, new_num, num;
num <span class="Keyword">=</span> <span class="Number">1</span>;
change_numbers <span class="Keyword">=</span> <span class="Storage">function</span> <span class="FunctionName">change_numbers</span>() {
<span class="Storage">var</span> new_num;
new_num <span class="Keyword">=</span> <span class="Keyword">-</span><span class="Number">1</span>;
<span class="Keyword">return</span> num <span class="Keyword">=</span> <span class="Number">10</span>;
};
new_num <span class="Keyword">=</span> change_numbers();
</pre><button onclick='javascript: var change_numbers, new_num, num;
num = 1;
change_numbers = function change_numbers() {
var new_num;
new_num = -1;
return num = 10;
};
new_num = change_numbers();
;alert(new_num);'>run: new_num</button><br class='clear' /></div>
<p>
Notice how the all of the variable declarations have been pushed up to
the top of the closest scope, the first time they appear.
<b>num</b> is not redeclared within the inner function, because it's
already in scope; the <b>new_num</b> within the function, on the other hand,
should not be able to change the value of the external variable of the same name, and
therefore has a declaration of its own.
</p>
<p>
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. If you'd like to create
global variables, attach them as properties on <b>window</b>,
or on the <b>exports</b> object in CommonJS.
</p>
<p id="conditionals">
<b class="header">Conditionals, Ternaries, and Conditional Assignment</b>
<b>If/else</b> statements can be written without the use of parentheses and
curly brackets. As with functions and other block expressions,
multi-line conditionals are delimited by indentation. There's also a handy
postfix form, with the <tt>if</tt> or <tt>unless</tt> at the end.
</p>
<p>
CoffeeScript will compile <b>if</b> statements using the ternary operator
when possible, to make it easier to use the result as an expression.
</p>
<div class='code'><pre class="idle"><span class="FunctionName">mood</span><span class="Keyword">:</span> greatly_improved <span class="Keyword">if</span> singing
<span class="Keyword">if</span> happy <span class="Keyword">and</span> knows_it
claps_hands()
cha_cha_cha()
<span class="FunctionName">date</span><span class="Keyword">:</span> <span class="Keyword">if</span> friday <span class="Keyword">then</span> sue <span class="Keyword">else</span> jill
expensive <span class="Keyword">||</span><span class="Keyword">=</span> do_the_math()
</pre><pre class="idle"><span class="Storage">var</span> date, expensive, mood;
<span class="Keyword">if</span> (singing) {
mood <span class="Keyword">=</span> greatly_improved;
}
<span class="Keyword">if</span> (happy <span class="Keyword">&</span><span class="Keyword">&</span> knows_it) {
claps_hands();
cha_cha_cha();
}
date <span class="Keyword">=</span> friday ? sue : jill;
expensive <span class="Keyword">=</span> expensive <span class="Keyword">||</span> do_the_math();
</pre><br class='clear' /></div>
<p>
The conditional assignment operators are included: <tt>||=</tt>,
which only assigns a value to a variable if the variable's current value
is falsy, and <tt>&&=</tt>, which only replaces the value of
truthy variables.
</p>
<p id="existence">
<b class="header">The Existential Operator</b>
It's a little difficult to check for the existence of a variable in
JavaScript. <tt>if (variable) ...</tt> comes close, but fails for zero,
the empty string, and false. The existential operator <tt>?</tt> returns true unless
a variable is <b>null</b> or <b>undefined</b>, which makes it analogous
to Ruby's <tt>nil?</tt>
</p>
<p>
It can also be used for safer conditional assignment than <tt>||=</tt>
provides, for cases where you may be handling numbers or strings.
</p>
<div class='code'><pre class="idle"><span class="FunctionName">solipsism</span><span class="Keyword">:</span> <span class="BuiltInConstant">true</span> <span class="Keyword">if</span> mind<span class="Keyword">?</span> <span class="Keyword">and</span> <span class="Keyword">not</span> world<span class="Keyword">?</span>
speed <span class="Keyword">?</span><span class="Keyword">=</span> <span class="Number">140</span>
</pre><pre class="idle"><span class="Storage">var</span> solipsism, speed;
<span class="Keyword">if</span> ((<span class="Keyword">typeof</span> mind <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> mind <span class="Keyword">!</span><span class="Keyword">==</span> <span class="BuiltInConstant">null</span>) <span class="Keyword">&</span><span class="Keyword">&</span> <span class="Keyword">!</span>(<span class="Keyword">typeof</span> world <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> world <span class="Keyword">!</span><span class="Keyword">==</span> <span class="BuiltInConstant">null</span>)) {
solipsism <span class="Keyword">=</span> <span class="BuiltInConstant">true</span>;
}
speed <span class="Keyword">=</span> (<span class="Keyword">typeof</span> speed <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> speed <span class="Keyword">!</span><span class="Keyword">==</span> <span class="BuiltInConstant">null</span>) ? speed : <span class="Number">140</span>;
</pre><button onclick='javascript: var solipsism, speed;
if ((typeof mind !== "undefined" && mind !== null) && !(typeof world !== "undefined" && world !== null)) {
solipsism = true;
}
speed = (typeof speed !== "undefined" && speed !== null) ? speed : 140;
;alert(speed);'>run: speed</button><br class='clear' /></div>
<p id="aliases">
<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>
<div class='code'><pre class="idle">launch() <span class="Keyword">if</span> ignition <span class="Keyword">is</span> <span class="BuiltInConstant">on</span>
<span class="FunctionName">volume</span><span class="Keyword">:</span> <span class="Number">10</span> <span class="Keyword">if</span> band <span class="Keyword">isnt</span> spinal_tap
let_the_wild_rumpus_begin() <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> speed_limit <span class="Keyword">then</span> accelerate()
</pre><pre class="idle"><span class="Storage">var</span> volume;
<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> spinal_tap) {
volume <span class="Keyword">=</span> <span class="Number">10</span>;
}
<span class="Keyword">if</span> (<span class="Keyword">!</span>(answer <span class="Keyword">===</span> <span class="BuiltInConstant">false</span>)) {
let_the_wild_rumpus_begin();
}
car.speed <span class="Keyword"><</span> speed_limit ? accelerate() : <span class="BuiltInConstant">null</span>;
</pre><br class='clear' /></div>
<p id="splats">
<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 arguments a little bit more palatable.
</p>
<div class='code'><pre class="idle"><span class="FunctionName">gold</span><span class="Keyword">:</span> <span class="FunctionName">silver</span><span class="Keyword">:</span> <span class="FunctionName">the_field</span><span class="Keyword">:</span> <span class="String"><span class="String">"</span>unknown<span class="String">"</span></span>
<span class="FunctionArgument">medalists: first, second, rest... </span><span class="Storage">=></span>
<span class="FunctionName">gold</span><span class="Keyword">:</span> first
<span class="FunctionName">silver</span><span class="Keyword">:</span> second
<span class="FunctionName">the_field</span><span class="Keyword">:</span> rest
<span class="FunctionName">contenders</span><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>
]
medalists(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> the_field)
</pre><pre class="idle"><span class="Storage">var</span> contenders, gold, medalists, silver, the_field;
gold <span class="Keyword">=</span> (silver <span class="Keyword">=</span> (the_field <span class="Keyword">=</span> <span class="String"><span class="String">"</span>unknown<span class="String">"</span></span>));
medalists <span class="Keyword">=</span> <span class="Storage">function</span> <span class="FunctionName">medalists</span>(<span class="FunctionArgument">first, second</span>) {
<span class="Storage">var</span> rest;
rest <span class="Keyword">=</span> <span class="LibraryClassType">Array</span>.<span class="LibraryConstant">prototype</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> the_field <span class="Keyword">=</span> rest;
};
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>];
medalists.<span class="LibraryFunction">apply</span>(<span class="Variable">this</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> the_field);
</pre><button onclick='javascript: var contenders, gold, medalists, silver, the_field;
gold = (silver = (the_field = "unknown"));
medalists = function medalists(first, second) {
var rest;
rest = Array.prototype.slice.call(arguments, 2);
gold = first;
silver = second;
return the_field = rest;
};
contenders = ["Michael Phelps", "Liu Xiang", "Yao Ming", "Allyson Felix", "Shawn Johnson", "Roman Sebrle", "Guo Jingjing", "Tyson Gay", "Asafa Powell", "Usain Bolt"];
medalists.apply(this, contenders);
alert("Gold: " + gold);
alert("Silver: " + silver);
alert("The Field: " + the_field);
;'>run</button><br class='clear' /></div>
<p id="arguments">
<b class="header">Arguments are Arrays</b>
If you reference the <b>arguments object</b> directly, it will be converted
into a real Array, making all of the
<a href="https://developer.mozilla.org/En/Core_JavaScript_1.5_Reference/Objects/Array">Array methods</a>
available.
</p>
<div class='code'><pre class="idle"><span class="FunctionName">backwards</span><span class="Keyword">:</span> <span class="Storage">=></span>
alert(arguments.reverse())
backwards(<span class="String"><span class="String">"</span>stairway<span class="String">"</span></span>, <span class="String"><span class="String">"</span>to<span class="String">"</span></span>, <span class="String"><span class="String">"</span>heaven<span class="String">"</span></span>)
</pre><pre class="idle"><span class="Storage">var</span> backwards;
backwards <span class="Keyword">=</span> <span class="Storage">function</span> <span class="FunctionName">backwards</span>() {
<span class="Storage">var</span> arguments <span class="Keyword">=</span> <span class="LibraryClassType">Array</span>.<span class="LibraryConstant">prototype</span>.slice.<span class="LibraryFunction">call</span>(arguments, <span class="Number">0</span>);
<span class="Keyword">return</span> <span class="LibraryFunction">alert</span>(arguments.<span class="LibraryFunction">reverse</span>());
};
backwards(<span class="String"><span class="String">"</span>stairway<span class="String">"</span></span>, <span class="String"><span class="String">"</span>to<span class="String">"</span></span>, <span class="String"><span class="String">"</span>heaven<span class="String">"</span></span>);
</pre><button onclick='javascript: var backwards;
backwards = function backwards() {
var arguments = Array.prototype.slice.call(arguments, 0);
return alert(arguments.reverse());
};
backwards("stairway", "to", "heaven");
;'>run</button><br class='clear' /></div>
<p id="while">
<b class="header">While 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="Keyword">if</span> <span class="Variable">this</span>.studying_economics
<span class="Keyword">while</span> supply <span class="Keyword">></span> demand <span class="Keyword">then</span> buy()
<span class="Keyword">while</span> supply <span class="Keyword"><</span> demand <span class="Keyword">then</span> sell()
<span class="FunctionName">num</span><span class="Keyword">:</span> <span class="Number">6</span>
<span class="FunctionName">lyrics</span><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> __a, lyrics, num;
<span class="Keyword">if</span> (<span class="Variable">this</span>.studying_economics) {
<span class="Keyword">while</span> (supply <span class="Keyword">></span> demand) {
buy();
}
<span class="Keyword">while</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>() {
__a <span class="Keyword">=</span> [];
<span class="Keyword">while</span> (num <span class="Keyword">-</span><span class="Keyword">=</span> <span class="Number">1</span>) {
__a.<span class="LibraryFunction">push</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>);
}
<span class="Keyword">return</span> __a;
})();
</pre><button onclick='javascript: var __a, lyrics, num;
if (this.studying_economics) {
while (supply > demand) {
buy();
}
while (supply < demand) {
sell();
}
}
num = 6;
lyrics = (function() {
__a = [];
while (num -= 1) {
__a.push(num + " little monkeys, jumping on the bed. \
One fell out and bumped his head.");
}
return __a;
})();
;alert(lyrics.join("\n"));'>run: lyrics.join("\n")</button><br class='clear' /></div>
<p>
Other JavaScript loops, such as <b>for</b> loops and <b>do-while</b> loops
can be mimicked by variations on <b>while</b>, but the hope is that you
won't need to do that with CoffeeScript, either because you're using
<b>each</b> (<b>forEach</b>) style iterators, or...
</p>
<p id="comprehensions">
<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>
<span class="FunctionName">lunch</span><span class="Keyword">:</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>]
<span class="Comment"><span class="Comment">#</span> Naive collision detection.</span>
<span class="Keyword">for</span> roid <span class="Keyword">in</span> asteroids
<span class="Keyword">for</span> roid2 <span class="Keyword">in</span> asteroids <span class="Keyword">when</span> roid <span class="Keyword">isnt</span> roid2
roid.explode() <span class="Keyword">if</span> roid.overlaps(roid2)
</pre><pre class="idle"><span class="Storage">var</span> __a, __b, __c, __d, __e, __f, __g, food, lunch, roid, roid2;
<span class="Comment"><span class="Comment">//</span> Eat lunch.</span>
lunch <span class="Keyword">=</span> (<span class="Storage">function</span>() {
__a <span class="Keyword">=</span> []; __b <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> (__c <span class="Keyword">=</span> <span class="Number">0</span>; __c <span class="Keyword"><</span> __b.<span class="LibraryConstant">length</span>; __c<span class="Keyword">++</span>) {
food <span class="Keyword">=</span> __b[__c];
__a.<span class="LibraryFunction">push</span>(eat(food));
}
<span class="Keyword">return</span> __a;
})();
<span class="Comment"><span class="Comment">//</span> Naive collision detection.</span>
__d <span class="Keyword">=</span> asteroids;
<span class="Keyword">for</span> (__e <span class="Keyword">=</span> <span class="Number">0</span>; __e <span class="Keyword"><</span> __d.<span class="LibraryConstant">length</span>; __e<span class="Keyword">++</span>) {
roid <span class="Keyword">=</span> __d[__e];
__f <span class="Keyword">=</span> asteroids;
<span class="Keyword">for</span> (__g <span class="Keyword">=</span> <span class="Number">0</span>; __g <span class="Keyword"><</span> __f.<span class="LibraryConstant">length</span>; __g<span class="Keyword">++</span>) {
roid2 <span class="Keyword">=</span> __f[__g];
<span class="Keyword">if</span> (roid <span class="Keyword">!</span><span class="Keyword">==</span> roid2) {
<span class="Keyword">if</span> (roid.overlaps(roid2)) {
roid.explode();
}
}
}
}
</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. (The long line-breaking "for" definitions in
the compiled JS below allow ranges to count downwards, as well as upwards).
</p>
<div class='code'><pre class="idle"><span class="FunctionName">countdown</span><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>]
<span class="FunctionName">egg_delivery</span><span class="Keyword">:</span> <span class="Storage">=></span>
<span class="Keyword">for</span> i <span class="Keyword">in</span> [<span class="Number">0</span>...eggs.length] <span class="Keyword">by</span> <span class="Number">12</span>
<span class="FunctionName">dozen_eggs</span><span class="Keyword">:</span> eggs[i...i<span class="Keyword">+</span><span class="Number">12</span>]
deliver(<span class="Keyword">new</span> <span class="TypeName">egg_carton</span>(dozen))
</pre><pre class="idle"><span class="Storage">var</span> __a, __b, __c, __d, __e, countdown, egg_delivery, num;
countdown <span class="Keyword">=</span> (<span class="Storage">function</span>() {
__a <span class="Keyword">=</span> []; __d <span class="Keyword">=</span> <span class="Number">10</span>; __e <span class="Keyword">=</span> <span class="Number">1</span>;
<span class="Keyword">for</span> (__c<span class="Keyword">=</span><span class="Number">0</span>, num<span class="Keyword">=</span>__d; (__d <span class="Keyword"><=</span> __e ? num <span class="Keyword"><=</span> __e : num <span class="Keyword">>=</span> __e); (__d <span class="Keyword"><=</span> __e ? num <span class="Keyword">+</span><span class="Keyword">=</span> <span class="Number">1</span> : num <span class="Keyword">-</span><span class="Keyword">=</span> <span class="Number">1</span>), __c<span class="Keyword">++</span>) {
__a.<span class="LibraryFunction">push</span>(num);
}
<span class="Keyword">return</span> __a;
})();
egg_delivery <span class="Keyword">=</span> <span class="Storage">function</span> <span class="FunctionName">egg_delivery</span>() {
<span class="Storage">var</span> __f, __g, __h, __i, __j, dozen_eggs, i;
__f <span class="Keyword">=</span> []; __i <span class="Keyword">=</span> <span class="Number">0</span>; __j <span class="Keyword">=</span> eggs.<span class="LibraryConstant">length</span>;
<span class="Keyword">for</span> (__h<span class="Keyword">=</span><span class="Number">0</span>, i<span class="Keyword">=</span>__i; (__i <span class="Keyword"><=</span> __j ? i <span class="Keyword"><</span> __j : i <span class="Keyword">></span> __j); (__i <span class="Keyword"><=</span> __j ? i <span class="Keyword">+</span><span class="Keyword">=</span> <span class="Number">12</span> : i <span class="Keyword">-</span><span class="Keyword">=</span> <span class="Number">12</span>), __h<span class="Keyword">++</span>) {
__f.<span class="LibraryFunction">push</span>((<span class="Storage">function</span>() {
dozen_eggs <span class="Keyword">=</span> eggs.<span class="LibraryFunction">slice</span>(i, i <span class="Keyword">+</span> <span class="Number">12</span>);
<span class="Keyword">return</span> deliver(<span class="Keyword">new</span> <span class="TypeName">egg_carton</span>(dozen));
})());
}
<span class="Keyword">return</span> __f;
};
</pre><button onclick='javascript: var __a, __b, __c, __d, __e, countdown, egg_delivery, num;
countdown = (function() {
__a = []; __d = 10; __e = 1;
for (__c=0, num=__d; (__d <= __e ? num <= __e : num >= __e); (__d <= __e ? num += 1 : num -= 1), __c++) {
__a.push(num);
}
return __a;
})();
egg_delivery = function egg_delivery() {
var __f, __g, __h, __i, __j, dozen_eggs, i;
__f = []; __i = 0; __j = eggs.length;
for (__h=0, i=__i; (__i <= __j ? i < __j : i > __j); (__i <= __j ? i += 12 : i -= 12), __h++) {
__f.push((function() {
dozen_eggs = eggs.slice(i, i + 12);
return deliver(new egg_carton(dozen));
})());
}
return __f;
};
;alert(countdown);'>run: countdown</button><br class='clear' /></div>
<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"><span class="FunctionName">years_old</span><span class="Keyword">:</span> {<span class="FunctionName">max</span><span class="Keyword">:</span> <span class="Number">10</span>, <span class="FunctionName">ida</span><span class="Keyword">:</span> <span class="Number">9</span>, <span class="FunctionName">tim</span><span class="Keyword">:</span> <span class="Number">11</span>}
<span class="FunctionName">ages</span><span class="Keyword">:</span> <span class="Keyword">for</span> child, age <span class="Keyword">of</span> years_old
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> __a, __b, age, ages, child, years_old;
<span class="Storage">var</span> __hasProp <span class="Keyword">=</span> <span class="LibraryClassType">Object</span>.<span class="LibraryConstant">prototype</span>.hasOwnProperty;
years_old <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>() {
__a <span class="Keyword">=</span> []; __b <span class="Keyword">=</span> years_old;
<span class="Keyword">for</span> (child <span class="Keyword">in</span> __b) {
age <span class="Keyword">=</span> __b[child];
<span class="Keyword">if</span> (__hasProp.<span class="LibraryFunction">call</span>(__b, child)) {
__a.<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> __a;
})();
</pre><button onclick='javascript: var __a, __b, age, ages, child, years_old;
var __hasProp = Object.prototype.hasOwnProperty;
years_old = {
max: 10,
ida: 9,
tim: 11
};
ages = (function() {
__a = []; __b = years_old;
for (child in __b) {
age = __b[child];
if (__hasProp.call(__b, child)) {
__a.push(child + " is " + age);
}
}
return __a;
})();
;alert(ages.join(", "));'>run: ages.join(", ")</button><br class='clear' /></div>
<p id="slice_splice">
<b class="header">Array Slicing and Splicing with Ranges</b>
CoffeeScript borrows Ruby's
<a href="http://ruby-doc.org/core/classes/Range.html">range syntax</a>
for extracting slices of arrays. With two dots (<tt>3..5</tt>), the range
is inclusive: the first argument is the index of the first element in
the slice, and the second is the index of the last one. Three dots signify
a range that excludes the end.
</p>
<div class='code'><pre class="idle"><span class="FunctionName">numbers</span><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>]
<span class="FunctionName">three_to_six</span><span class="Keyword">:</span> numbers[<span class="Number">3</span>..<span class="Number">6</span>]
<span class="FunctionName">numbers_copy</span><span class="Keyword">:</span> numbers[<span class="Number">0</span>...numbers.length]
</pre><pre class="idle"><span class="Storage">var</span> numbers, numbers_copy, three_to_six;
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>];
three_to_six <span class="Keyword">=</span> numbers.<span class="LibraryFunction">slice</span>(<span class="Number">3</span>, <span class="Number">6</span> <span class="Keyword">+</span> <span class="Number">1</span>);
numbers_copy <span class="Keyword">=</span> numbers.<span class="LibraryFunction">slice</span>(<span class="Number">0</span>, numbers.<span class="LibraryConstant">length</span>);
</pre><button onclick='javascript: var numbers, numbers_copy, three_to_six;
numbers = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9];
three_to_six = numbers.slice(3, 6 + 1);
numbers_copy = numbers.slice(0, numbers.length);
;alert(numbers_copy);'>run: numbers_copy</button><br class='clear' /></div>
<p>
The same syntax can be used with assignment to replace a segment of an
array with new values (to splice it).
</p>
<div class='code'><pre class="idle"><span class="FunctionName">numbers</span><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>];
numbers.splice.<span class="LibraryFunction">apply</span>(numbers, [<span class="Number">3</span>, <span class="Number">6</span> <span class="Keyword">-</span> <span class="Number">3</span> <span class="Keyword">+</span> <span class="Number">1</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];
numbers.splice.apply(numbers, [3, 6 - 3 + 1].concat([-3, -4, -5, -6]));
;alert(numbers);'>run: numbers</button><br class='clear' /></div>
<p id="expressions">
<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.excellent_work
<span class="String"><span class="String">"</span>A+<span class="String">"</span></span>
<span class="Keyword">else</span> <span class="Keyword">if</span> student.okay_stuff
<span class="Keyword">if</span> student.tried_hard <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>
<span class="FunctionName">eldest</span><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;
grade <span class="Keyword">=</span> <span class="Storage">function</span> <span class="FunctionName">grade</span>(<span class="FunctionArgument">student</span>) {
<span class="Keyword">if</span> (student.excellent_work) {
<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.okay_stuff) {
<span class="Keyword">return</span> student.tried_hard ? <span class="String"><span class="String">"</span>B<span class="String">"</span></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><button onclick='javascript: var eldest, grade;
grade = function grade(student) {
if (student.excellent_work) {
return "A+";
} else if (student.okay_stuff) {
return student.tried_hard ? "B" : "B-";
} else {
return "C";
}
};
eldest = 24 > 21 ? "Liz" : "Ike";
;alert(eldest);'>run: eldest</button><br class='clear' /></div>
<p>
Even though functions will always return their final value, it's both possible
and encouraged to return early from a function body writing out the explicit
return (<tt>return value</tt>), when you know that you're done.
</p>
<p>
Because variable declarations occur at the top of scope, assignment can
be used within expressions, even for variables that haven't been seen before:
</p>
<div class='code'><pre class="idle"><span class="FunctionName">six</span><span class="Keyword">:</span> (<span class="FunctionName">one</span><span class="Keyword">:</span> <span class="Number">1</span>) <span class="Keyword">+</span> (<span class="FunctionName">two</span><span class="Keyword">:</span> <span class="Number">2</span>) <span class="Keyword">+</span> (<span class="FunctionName">three</span><span class="Keyword">:</span> <span class="Number">3</span>)
</pre><pre class="idle"><span class="Storage">var</span> one, six, three, two;
six <span class="Keyword">=</span> ((one <span class="Keyword">=</span> <span class="Number">1</span>)) <span class="Keyword">+</span> ((two <span class="Keyword">=</span> <span class="Number">2</span>)) <span class="Keyword">+</span> ((three <span class="Keyword">=</span> <span class="Number">3</span>));
</pre><button onclick='javascript: var one, six, three, two;
six = ((one = 1)) + ((two = 2)) + ((three = 3));
;alert(six);'>run: six</button><br class='clear' /></div>
<p>
Things that would otherwise be statements in JavaScript, when used
as part of an expression in CoffeeScript, are converted into expressions
by wrapping them in a closure. This lets you do useful things, like assign
the result of a comprehension to a variable:
</p>
<div class='code'><pre class="idle"><span class="Comment"><span class="Comment">#</span> The first ten global properties.</span>
<span class="FunctionName">globals</span><span class="Keyword">:</span> (name <span class="Keyword">for</span> name <span class="Keyword">of</span> window)[<span class="Number">0</span>...<span class="Number">10</span>]
</pre><pre class="idle"><span class="Storage">var</span> __a, __b, globals, name;
<span class="Storage">var</span> __hasProp <span class="Keyword">=</span> <span class="LibraryClassType">Object</span>.<span class="LibraryConstant">prototype</span>.hasOwnProperty;
<span class="Comment"><span class="Comment">//</span> The first ten global properties.</span>
globals <span class="Keyword">=</span> ((<span class="Storage">function</span>() {
__a <span class="Keyword">=</span> []; __b <span class="Keyword">=</span> <span class="LibraryClassType">window</span>;
<span class="Keyword">for</span> (name <span class="Keyword">in</span> __b) {
<span class="Keyword">if</span> (__hasProp.<span class="LibraryFunction">call</span>(__b, name)) {
__a.<span class="LibraryFunction">push</span>(name);
}