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<title>CoffeeScript</title>
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<h1><sub style="font-size: 100px;">&#9749;</sub> CoffeeScript</h1>
<p>
CoffeeScript is a little language that compiles into JavaScript. Think
of it as JavaScript's less ostentatious kid brother &mdash; 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 &mdash; 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">=&gt;</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">=&gt;</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">=&gt;</span>
print(winner, runners)
<span class="Comment"><span class="Comment">#</span> Existence:</span>
alert(<span class="String"><span class="String">&quot;</span>I knew it!<span class="String">&quot;</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">&quot;</span>undefined<span class="String">&quot;</span></span> <span class="Keyword">&amp;</span><span class="Keyword">&amp;</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">&quot;</span>I knew it!<span class="String">&quot;</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">&lt;</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 determine that the line hasn't finished yet.
</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 easier debugging.
</p>
<div class='code'><pre class="idle"><span class="FunctionName">square</span><span class="Keyword">:</span> <span class="FunctionArgument">x</span> <span class="Storage">=&gt;</span> x <span class="Keyword">*</span> x
<span class="FunctionName">cube</span><span class="Keyword">:</span> <span class="FunctionArgument">x</span> <span class="Storage">=&gt;</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>
If you'd like to create an anonymous function, just wrap it in parentheses:
<tt>(x => x * x)</tt>
</p>
<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">&quot;</span>Hello CoffeeScript<span class="String">&quot;</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">&quot;</span>Hello CoffeeScript<span class="String">&quot;</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>
Declaration 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. Feel free to 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">&quot;</span>do<span class="String">&quot;</span></span>, <span class="String"><span class="String">&quot;</span>re<span class="String">&quot;</span></span>, <span class="String"><span class="String">&quot;</span>mi<span class="String">&quot;</span></span>, <span class="String"><span class="String">&quot;</span>fa<span class="String">&quot;</span></span>, <span class="String"><span class="String">&quot;</span>so<span class="String">&quot;</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">&quot;</span>do<span class="String">&quot;</span></span>, <span class="String"><span class="String">&quot;</span>re<span class="String">&quot;</span></span>, <span class="String"><span class="String">&quot;</span>mi<span class="String">&quot;</span></span>, <span class="String"><span class="String">&quot;</span>fa<span class="String">&quot;</span></span>, <span class="String"><span class="String">&quot;</span>so<span class="String">&quot;</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 &mdash; 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">=&gt;</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.
</p>
<p>
If you'd like to create top-level variables for other scripts to use,
attach them as properties on <b>window</b>, or on the <b>exports</b>
object in CommonJS. The <b>existential operator</b> (below), gives you a
reliable way to figure out where to add them, if you're targeting both
CommonJS and the browser: <tt>root: exports ? this</tt>
</p>
<p 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">&amp;</span><span class="Keyword">&amp;</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>&amp;&amp;=</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">&quot;</span>undefined<span class="String">&quot;</span></span> <span class="Keyword">&amp;</span><span class="Keyword">&amp;</span> mind <span class="Keyword">!</span><span class="Keyword">==</span> <span class="BuiltInConstant">null</span>) <span class="Keyword">&amp;</span><span class="Keyword">&amp;</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">&quot;</span>undefined<span class="String">&quot;</span></span> <span class="Keyword">&amp;</span><span class="Keyword">&amp;</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">&quot;</span>undefined<span class="String">&quot;</span></span> <span class="Keyword">&amp;</span><span class="Keyword">&amp;</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>&amp;&amp;</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">&lt;</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">&lt;</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 numbers of 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">&quot;</span>unknown<span class="String">&quot;</span></span>
<span class="FunctionArgument">medalists: first, second, rest... </span><span class="Storage">=&gt;</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">&quot;</span>Michael Phelps<span class="String">&quot;</span></span>
<span class="String"><span class="String">&quot;</span>Liu Xiang<span class="String">&quot;</span></span>
<span class="String"><span class="String">&quot;</span>Yao Ming<span class="String">&quot;</span></span>
<span class="String"><span class="String">&quot;</span>Allyson Felix<span class="String">&quot;</span></span>
<span class="String"><span class="String">&quot;</span>Shawn Johnson<span class="String">&quot;</span></span>
<span class="String"><span class="String">&quot;</span>Roman Sebrle<span class="String">&quot;</span></span>
<span class="String"><span class="String">&quot;</span>Guo Jingjing<span class="String">&quot;</span></span>
<span class="String"><span class="String">&quot;</span>Tyson Gay<span class="String">&quot;</span></span>
<span class="String"><span class="String">&quot;</span>Asafa Powell<span class="String">&quot;</span></span>
<span class="String"><span class="String">&quot;</span>Usain Bolt<span class="String">&quot;</span></span>
]
medalists(contenders...)
alert(<span class="String"><span class="String">&quot;</span>Gold: <span class="String">&quot;</span></span> <span class="Keyword">+</span> gold)
alert(<span class="String"><span class="String">&quot;</span>Silver: <span class="String">&quot;</span></span> <span class="Keyword">+</span> silver)
alert(<span class="String"><span class="String">&quot;</span>The Field: <span class="String">&quot;</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">&quot;</span>unknown<span class="String">&quot;</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">&quot;</span>Michael Phelps<span class="String">&quot;</span></span>, <span class="String"><span class="String">&quot;</span>Liu Xiang<span class="String">&quot;</span></span>, <span class="String"><span class="String">&quot;</span>Yao Ming<span class="String">&quot;</span></span>, <span class="String"><span class="String">&quot;</span>Allyson Felix<span class="String">&quot;</span></span>, <span class="String"><span class="String">&quot;</span>Shawn Johnson<span class="String">&quot;</span></span>, <span class="String"><span class="String">&quot;</span>Roman Sebrle<span class="String">&quot;</span></span>, <span class="String"><span class="String">&quot;</span>Guo Jingjing<span class="String">&quot;</span></span>, <span class="String"><span class="String">&quot;</span>Tyson Gay<span class="String">&quot;</span></span>, <span class="String"><span class="String">&quot;</span>Asafa Powell<span class="String">&quot;</span></span>, <span class="String"><span class="String">&quot;</span>Usain Bolt<span class="String">&quot;</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">&quot;</span>Gold: <span class="String">&quot;</span></span> <span class="Keyword">+</span> gold);
<span class="LibraryFunction">alert</span>(<span class="String"><span class="String">&quot;</span>Silver: <span class="String">&quot;</span></span> <span class="Keyword">+</span> silver);
<span class="LibraryFunction">alert</span>(<span class="String"><span class="String">&quot;</span>The Field: <span class="String">&quot;</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">=&gt;</span>
alert(arguments.reverse())
backwards(<span class="String"><span class="String">&quot;</span>stairway<span class="String">&quot;</span></span>, <span class="String"><span class="String">&quot;</span>to<span class="String">&quot;</span></span>, <span class="String"><span class="String">&quot;</span>heaven<span class="String">&quot;</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">&quot;</span>stairway<span class="String">&quot;</span></span>, <span class="String"><span class="String">&quot;</span>to<span class="String">&quot;</span></span>, <span class="String"><span class="String">&quot;</span>heaven<span class="String">&quot;</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="Comment"><span class="Comment">#</span> Econ 101</span>
<span class="Keyword">if</span> <span class="Variable">this</span>.studying_economics
<span class="Keyword">while</span> supply <span class="Keyword">&gt;</span> demand <span class="Keyword">then</span> buy()
<span class="Keyword">while</span> supply <span class="Keyword">&lt;</span> demand <span class="Keyword">then</span> sell()
<span class="Comment"><span class="Comment">#</span> Nursery Rhyme</span>
<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">&quot;</span> little monkeys, jumping on the bed.</span>
<span class="String"> One fell out and bumped his head.<span class="String">&quot;</span></span>
</pre><pre class="idle"><span class="Storage">var</span> __a, lyrics, num;
<span class="Comment"><span class="Comment">//</span> Econ 101</span>
<span class="Keyword">if</span> (<span class="Variable">this</span>.studying_economics) {
<span class="Keyword">while</span> (supply <span class="Keyword">&gt;</span> demand) {
buy();
}
<span class="Keyword">while</span> (supply <span class="Keyword">&lt;</span> demand) {
sell();
}
}
<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="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">&quot;</span> little monkeys, jumping on the bed. \</span>
<span class="String">One fell out and bumped his head.<span class="String">&quot;</span></span>);
}
<span class="Keyword">return</span> __a;
})();
</pre><button onclick='javascript: var __a, lyrics, num;
// Econ 101
if (this.studying_economics) {
while (supply > demand) {
buy();
}
while (supply < demand) {
sell();
}
}
// Nursery Rhyme
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">&lt;</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">&lt;</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">&lt;</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">=&gt;</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">&lt;=</span> __e ? num <span class="Keyword">&lt;=</span> __e : num <span class="Keyword">&gt;=</span> __e); (__d <span class="Keyword">&lt;=</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">&lt;=</span> __j ? i <span class="Keyword">&lt;</span> __j : i <span class="Keyword">&gt;</span> __j); (__i <span class="Keyword">&lt;=</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">&quot;</span> is <span class="String">&quot;</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">&quot;</span> is <span class="String">&quot;</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">=&gt;</span>
<span class="Keyword">if</span> student.excellent_work
<span class="String"><span class="String">&quot;</span>A+<span class="String">&quot;</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">&quot;</span>B<span class="String">&quot;</span></span> <span class="Keyword">else</span> <span class="String"><span class="String">&quot;</span>B-<span class="String">&quot;</span></span>
<span class="Keyword">else</span>
<span class="String"><span class="String">&quot;</span>C<span class="String">&quot;</span></span>
<span class="FunctionName">eldest</span><span class="Keyword">:</span> <span class="Keyword">if</span> <span class="Number">24</span> <span class="Keyword">&gt;</span> <span class="Number">21</span> <span class="Keyword">then</span> <span class="String"><span class="String">&quot;</span>Liz<span class="String">&quot;</span></span> <span class="Keyword">else</span> <span class="String"><span class="String">&quot;</span>Ike<span class="String">&quot;</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">&quot;</span>A+<span class="String">&quot;</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">&quot;</span>B<span class="String">&quot;</span></span> : <span class="String"><span class="String">&quot;</span>B-<span class="String">&quot;</span></span>;
} <span class="Keyword">else</span> {
<span class="Keyword">return</span> <span class="String"><span class="String">&quot;</span>C<span class="String">&quot;</span></span>;
}
};
eldest <span class="Keyword">=</span> <span class="Number">24</span> <span class="Keyword">&gt;</span> <span class="Number">21</span> ? <span class="String"><span class="String">&quot;</span>Liz<span class="String">&quot;</span></span> : <span class="String"><span class="String">&quot;</span>Ike<span class="String">&quot;</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);
}
}
<span class="Keyword">return</span> __a;
})()).<span class="LibraryFunction">slice</span>(<span class="Number">0</span>, <span class="Number">10</span>);
</pre><button onclick='javascript: var __a, __b, globals, name;
var __hasProp = Object.prototype.hasOwnProperty;
// The first ten global properties.
globals = ((function() {
__a = []; __b = window;
for (name in __b) {
if (__hasProp.call(__b, name)) {
__a.push(name);
}
}
return __a;
})()).slice(0, 10);
;alert(globals);'>run: globals</button><br class='clear' /></div>
<p>
As well as silly things, like passing a <b>try/catch</b> statement directly
into a function call:
</p>
<div class='code'><pre class="idle">alert(
<span class="Keyword">try</span>
nonexistent <span class="Keyword">/</span> <span class="BuiltInConstant">undefined</span>
<span class="Keyword">catch</span> error
<span class="String"><span class="String">&quot;</span>And the error is ... <span class="String">&quot;</span></span> <span class="Keyword">+</span> error
)
</pre><pre class="idle"><span class="LibraryFunction">alert</span>((<span class="Storage">function</span>() {
<span class="Keyword">try</span> {
<span class="Keyword">return</span> nonexistent / undefined;
} <span class="Keyword">catch</span> (error) {
<span class="Keyword">return</span> <span class="String"><span class="String">&quot;</span>And the error is ... <span class="String">&quot;</span></span> <span class="Keyword">+</span> error;
}
})());
</pre><button onclick='javascript: alert((function() {
try {
return nonexistent / undefined;
} catch (error) {
return "And the error is ... " + error;
}
})());
;'>run</button><br class='clear' /></div>
<p>
There are a handful of statements in JavaScript that can't be meaningfully
converted into expressions, namely <tt>break</tt>, <tt>continue</tt>,
and <tt>return</tt>. If you make use of them within a block of code,
CoffeeScript won't try to perform the conversion.
</p>
<p id="inheritance">
<b class="header">Inheritance, and Calling Super from a Subclass</b>
JavaScript's prototypal inheritance has always been a bit of a
brain-bender, with a whole family tree of libraries that provide a cleaner
syntax for classical inheritance on top of JavaScript's prototypes:
<a href="http://code.google.com/p/base2/">Base2</a>,
<a href="http://prototypejs.org/">Prototype.js</a>,
<a href="http://jsclass.jcoglan.com/">JS.Class</a>, etc.
The libraries provide syntactic sugar, but the built-in inheritance would
be completely usable if it weren't for a couple of small exceptions:
it's awkward to call <b>super</b> (the prototype object's
implementation of the current function), and it's awkward to correctly
set the prototype chain.
</p>
<p>
CoffeeScript provides <tt>extends</tt>
to help with prototype setup, <tt>::</tt> for quick access to an
object's prototype, and converts <tt>super()</tt> into a call against
the immediate ancestor's method of the same name.
</p>
<div class='code'><pre class="idle"><span class="FunctionName">Animal</span><span class="Keyword">:</span> <span class="Storage">=&gt;</span>
<span class="FunctionName">Animal::move</span><span class="Keyword">:</span> <span class="FunctionArgument">meters</span> <span class="Storage">=&gt;</span>
alert(<span class="Variable">this</span>.name <span class="Keyword">+</span> <span class="String"><span class="String">&quot;</span> moved <span class="String">&quot;</span></span> <span class="Keyword">+</span> meters <span class="Keyword">+</span> <span class="String"><span class="String">&quot;</span>m.<span class="String">&quot;</span></span>)
<span class="FunctionName">Snake</span><span class="Keyword">:</span> <span class="FunctionArgument">name</span> <span class="Storage">=&gt;</span> <span class="FunctionName">this.name</span><span class="Keyword">:</span> name
Snake <span class="Variable">extends</span> Animal
<span class="FunctionName">Snake::move</span><span class="Keyword">:</span> <span class="Storage">=&gt;</span>
alert(<span class="String"><span class="String">&quot;</span>Slithering...<span class="String">&quot;</span></span>)
<span class="Variable">super</span>(<span class="Number">5</span>)
<span class="FunctionName">Horse</span><span class="Keyword">:</span> <span class="FunctionArgument">name</span> <span class="Storage">=&gt;</span> <span class="FunctionName">this.name</span><span class="Keyword">:</span> name
Horse <span class="Variable">extends</span> Animal
<span class="FunctionName">Horse::move</span><span class="Keyword">:</span> <span class="Storage">=&gt;</span>
alert(<span class="String"><span class="String">&quot;</span>Galloping...<span class="String">&quot;</span></span>)
<span class="Variable">super</span>(<span class="Number">45</span>)
<span class="FunctionName">sam</span><span class="Keyword">:</span> <span class="Keyword">new</span> <span class="TypeName">Snake</span>(<span class="String"><span class="String">&quot;</span>Sammy the Python<span class="String">&quot;</span></span>)
<span class="FunctionName">tom</span><span class="Keyword">:</span> <span class="Keyword">new</span> <span class="TypeName">Horse</span>(<span class="String"><span class="String">&quot;</span>Tommy the Palomino<span class="String">&quot;</span></span>)
sam.move()
tom.move()
</pre><pre class="idle"><span class="Storage">var</span> Animal, Horse, Snake, __a, __b, sam, tom;
Animal <span class="Keyword">=</span> <span class="Storage">function</span> <span class="FunctionName">Animal</span>() { };
<span class="LibraryClassType">Animal</span>.<span class="LibraryConstant">prototype</span>.<span class="FunctionName">move</span> = <span class="Storage">function</span> <span class="FunctionName">move</span>(<span class="FunctionArgument">meters</span>) {
<span class="Keyword">return</span> <span class="LibraryFunction">alert</span>(<span class="Variable">this</span>.<span class="LibraryConstant">name</span> <span class="Keyword">+</span> <span class="String"><span class="String">&quot;</span> moved <span class="String">&quot;</span></span> <span class="Keyword">+</span> meters <span class="Keyword">+</span> <span class="String"><span class="String">&quot;</span>m.<span class="String">&quot;</span></span>);
};
Snake <span class="Keyword">=</span> <span class="Storage">function</span> <span class="FunctionName">Snake</span>(<span class="FunctionArgument">name</span>) {
<span class="Storage">var</span> __a;
__a <span class="Keyword">=</span> <span class="Variable">this</span>.<span class="LibraryConstant">name</span> <span class="Keyword">=</span> name;
<span class="Keyword">return</span> Snake <span class="Keyword">===</span> <span class="Variable">this</span>.<span class="LibraryConstant">constructor</span> ? <span class="Variable">this</span> : __a;
};
<span class="FunctionName">__a</span> = <span class="Storage">function</span>(){};
<span class="LibraryClassType">__a</span>.<span class="LibraryConstant">prototype</span> = Animal.<span class="LibraryConstant">prototype</span>;
Snake.__superClass__ <span class="Keyword">=</span> Animal.<span class="LibraryConstant">prototype</span>;
<span class="LibraryClassType">Snake</span>.<span class="LibraryConstant">prototype</span> = <span class="Keyword">new</span> <span class="TypeName">__a</span>();
<span class="LibraryClassType">Snake</span>.<span class="LibraryConstant">prototype</span>.<span class="FunctionName">constructor</span> = Snake;
<span class="LibraryClassType">Snake</span>.<span class="LibraryConstant">prototype</span>.<span class="FunctionName">move</span> = <span class="Storage">function</span> <span class="FunctionName">move</span>() {
<span class="LibraryFunction">alert</span>(<span class="String"><span class="String">&quot;</span>Slithering...<span class="String">&quot;</span></span>);
<span class="Keyword">return</span> Snake.__superClass__.move.<span class="LibraryFunction">call</span>(<span class="Variable">this</span>, <span class="Number">5</span>);
};
Horse <span class="Keyword">=</span> <span class="Storage">function</span> <span class="FunctionName">Horse</span>(<span class="FunctionArgument">name</span>) {
<span class="Storage">var</span> __b;
__b <span class="Keyword">=</span> <span class="Variable">this</span>.<span class="LibraryConstant">name</span> <span class="Keyword">=</span> name;
<span class="Keyword">return</span> Horse <span class="Keyword">===</span> <span class="Variable">this</span>.<span class="LibraryConstant">constructor</span> ? <span class="Variable">this</span> : __b;
};
<span class="FunctionName">__b</span> = <span class="Storage">function</span>(){};
<span class="LibraryClassType">__b</span>.<span class="LibraryConstant">prototype</span> = Animal.<span class="LibraryConstant">prototype</span>;
Horse.__superClass__ <span class="Keyword">=</span> Animal.<span class="LibraryConstant">prototype</span>;
<span class="LibraryClassType">Horse</span>.<span class="LibraryConstant">prototype</span> = <span class="Keyword">new</span> <span class="TypeName">__b</span>();
<span class="LibraryClassType">Horse</span>.<span class="LibraryConstant">prototype</span>.<span class="FunctionName">constructor</span> = Horse;
<span class="LibraryClassType">Horse</span>.<span class="LibraryConstant">prototype</span>.<span class="FunctionName">move</span> = <span class="Storage">function</span> <span class="FunctionName">move</span>() {
<span class="LibraryFunction">alert</span>(<span class="String"><span class="String">&quot;</span>Galloping...<span class="String">&quot;</span></span>);
<span class="Keyword">return</span> Horse.__superClass__.move.<span class="LibraryFunction">call</span>(<span class="Variable">this</span>, <span class="Number">45</span>);
};
sam <span class="Keyword">=</span> <span class="Keyword">new</span> <span class="TypeName">Snake</span>(<span class="String"><span class="String">&quot;</span>Sammy the Python<span class="String">&quot;</span></span>);
tom <span class="Keyword">=</span> <span class="Keyword">new</span> <span class="TypeName">Horse</span>(<span class="String"><span class="String">&quot;</span>Tommy the Palomino<span class="String">&quot;</span></span>);
sam.move();
tom.move();
</pre><button onclick='javascript: var Animal, Horse, Snake, __a, __b, sam, tom;
Animal = function Animal() { };
Animal.prototype.move = function move(meters) {
return alert(this.name + " moved " + meters + "m.");
};
Snake = function Snake(name) {
var __a;
__a = this.name = name;
return Snake === this.constructor ? this : __a;
};
__a = function(){};
__a.prototype = Animal.prototype;
Snake.__superClass__ = Animal.prototype;
Snake.prototype = new __a();
Snake.prototype.constructor = Snake;
Snake.prototype.move = function move() {
alert("Slithering...");
return Snake.__superClass__.move.call(this, 5);
};
Horse = function Horse(name) {
var __b;
__b = this.name = name;
return Horse === this.constructor ? this : __b;
};
__b = function(){};
__b.prototype = Animal.prototype;
Horse.__superClass__ = Animal.prototype;
Horse.prototype = new __b();
Horse.prototype.constructor = Horse;
Horse.prototype.move = function move() {
alert("Galloping...");
return Horse.__superClass__.move.call(this, 45);
};
sam = new Snake("Sammy the Python");
tom = new Horse("Tommy the Palomino");
sam.move();
tom.move();
;'>run</button><br class='clear' /></div>
<p id="blocks">
<b class="header">Blocks</b>
Many common looping functions (in Prototype, jQuery, and Underscore,
for example) take a single function as their final argument. To make
final functions easier to pass, CoffeeScript includes block syntax,
so you don't have to close the parentheses on the other side.
</p>
<div class='code'><pre class="idle">$(<span class="String"><span class="String">'</span>table.list<span class="String">'</span></span>).each()<span class="FunctionArgument"> table </span><span class="Storage">=&gt;</span>
$(<span class="String"><span class="String">'</span>tr.account<span class="String">'</span></span>, table).each()<span class="FunctionArgument"> row </span><span class="Storage">=&gt;</span>
row.show()
row.highlight()
</pre><pre class="idle"><span class="Keyword">$</span>(<span class="String"><span class="String">'</span>table.list<span class="String">'</span></span>).each(<span class="Storage">function</span>(table) {
<span class="Keyword">return</span> <span class="Keyword">$</span>(<span class="String"><span class="String">'</span>tr.account<span class="String">'</span></span>, table).each(<span class="Storage">function</span>(row) {
row.show();
<span class="Keyword">return</span> row.highlight();
});
});
</pre><br class='clear' /></div>
<p>
If you prefer not to use blocks, you'll need to add a pair of parentheses
to help distinguish the arguments from the definition of the function:
<tt>_.map(array, (num => num * 2))</tt>
</p>
<p id="pattern_matching">
<b class="header">Pattern Matching (Destructuring Assignment)</b>
To make extracting values from complex arrays and objects more convenient,
CoffeeScript implements ECMAScript Harmony's proposed
<a href="http://wiki.ecmascript.org/doku.php?id=harmony:destructuring">destructuring assignment</a>
syntax. When you assign an array or object literal to a value, CoffeeScript
breaks up and matches both sides against each other, assigning the values
on the right to the variables on the left. In the simplest case, it can be
used for parallel assignment:
</p>
<div class='code'><pre class="idle"><span class="FunctionName">bait</span><span class="Keyword">:</span> <span class="Number">1000</span>
<span class="FunctionName">and_switch</span><span class="Keyword">:</span> <span class="Number">0</span>
[bait, and_switch]<span class="Keyword">:</span> [and_switch, bait]
</pre><pre class="idle"><span class="Storage">var</span> __a, and_switch, bait;
bait <span class="Keyword">=</span> <span class="Number">1000</span>;
and_switch <span class="Keyword">=</span> <span class="Number">0</span>;
__a <span class="Keyword">=</span> [and_switch, bait];
bait <span class="Keyword">=</span> __a[<span class="Number">0</span>];
and_switch <span class="Keyword">=</span> __a[<span class="Number">1</span>];
</pre><button onclick='javascript: var __a, and_switch, bait;
bait = 1000;
and_switch = 0;
__a = [and_switch, bait];
bait = __a[0];
and_switch = __a[1];
;alert(bait);'>run: bait</button><br class='clear' /></div>
<p>
But it's also helpful for dealing with functions that return multiple
values.
</p>
<div class='code'><pre class="idle"><span class="FunctionName">weather_report</span><span class="Keyword">:</span> <span class="FunctionArgument">location</span> <span class="Storage">=&gt;</span>
<span class="Comment"><span class="Comment">#</span> Make an Ajax request to fetch the weather...</span>
[location, <span class="Number">72</span>, <span class="String"><span class="String">&quot;</span>Mostly Sunny<span class="String">&quot;</span></span>]
[city, temp, forecast]<span class="Keyword">:</span> weather_report(<span class="String"><span class="String">&quot;</span>Berkeley, CA<span class="String">&quot;</span></span>)
</pre><pre class="idle"><span class="Storage">var</span> __a, city, forecast, temp, weather_report;
weather_report <span class="Keyword">=</span> <span class="Storage">function</span> <span class="FunctionName">weather_report</span>(<span class="FunctionArgument">location</span>) {
<span class="Comment"><span class="Comment">//</span> Make an Ajax request to fetch the weather...</span>
<span class="Keyword">return</span> [location, <span class="Number">72</span>, <span class="String"><span class="String">&quot;</span>Mostly Sunny<span class="String">&quot;</span></span>];
};
__a <span class="Keyword">=</span> weather_report(<span class="String"><span class="String">&quot;</span>Berkeley, CA<span class="String">&quot;</span></span>);
city <span class="Keyword">=</span> __a[<span class="Number">0</span>];
temp <span class="Keyword">=</span> __a[<span class="Number">1</span>];
forecast <span class="Keyword">=</span> __a[<span class="Number">2</span>];
</pre><button onclick='javascript: var __a, city, forecast, temp, weather_report;
weather_report = function weather_report(location) {
// Make an Ajax request to fetch the weather...
return [location, 72, "Mostly Sunny"];
};
__a = weather_report("Berkeley, CA");
city = __a[0];
temp = __a[1];
forecast = __a[2];
;alert(forecast);'>run: forecast</button><br class='clear' /></div>
<p>
Pattern matching can be used with any depth of array and object nesting,
to help pull out deeply nested properties.
</p>
<div class='code'><pre class="idle"><span class="FunctionName">futurists</span><span class="Keyword">:</span> {
<span class="FunctionName">sculptor</span><span class="Keyword">:</span> <span class="String"><span class="String">&quot;</span>Umberto Boccioni<span class="String">&quot;</span></span>
<span class="FunctionName">painter</span><span class="Keyword">:</span> <span class="String"><span class="String">&quot;</span>Vladimir Burliuk<span class="String">&quot;</span></span>
<span class="FunctionName">poet</span><span class="Keyword">:</span> {
<span class="FunctionName">name</span><span class="Keyword">:</span> <span class="String"><span class="String">&quot;</span>F.T. Marinetti<span class="String">&quot;</span></span>
<span class="FunctionName">address</span><span class="Keyword">:</span> [
<span class="String"><span class="String">&quot;</span>Via Roma 42R<span class="String">&quot;</span></span>
<span class="String"><span class="String">&quot;</span>Bellagio, Italy 22021<span class="String">&quot;</span></span>
]
}
}
{<span class="FunctionName">poet</span><span class="Keyword">:</span> {<span class="FunctionName">name</span><span class="Keyword">:</span> poet, <span class="FunctionName">address</span><span class="Keyword">:</span> [street, city]}}<span class="Keyword">:</span> futurists
</pre><pre class="idle"><span class="Storage">var</span> __a, __b, __c, city, futurists, poet, street;
futurists <span class="Keyword">=</span> {
sculptor: <span class="String"><span class="String">&quot;</span>Umberto Boccioni<span class="String">&quot;</span></span>,
painter: <span class="String"><span class="String">&quot;</span>Vladimir Burliuk<span class="String">&quot;</span></span>,
poet: {
name: <span class="String"><span class="String">&quot;</span>F.T. Marinetti<span class="String">&quot;</span></span>,
address: [<span class="String"><span class="String">&quot;</span>Via Roma 42R<span class="String">&quot;</span></span>, <span class="String"><span class="String">&quot;</span>Bellagio, Italy 22021<span class="String">&quot;</span></span>]
}
};
__a <span class="Keyword">=</span> futurists;
__b <span class="Keyword">=</span> __a.poet;
poet <span class="Keyword">=</span> __b.<span class="LibraryConstant">name</span>;
__c <span class="Keyword">=</span> __b.address;
street <span class="Keyword">=</span> __c[<span class="Number">0</span>];
city <span class="Keyword">=</span> __c[<span class="Number">1</span>];
</pre><button onclick='javascript: var __a, __b, __c, city, futurists, poet, street;
futurists = {
sculptor: "Umberto Boccioni",
painter: "Vladimir Burliuk",
poet: {
name: "F.T. Marinetti",
address: ["Via Roma 42R", "Bellagio, Italy 22021"]
}
};
__a = futurists;
__b = __a.poet;
poet = __b.name;
__c = __b.address;
street = __c[0];
city = __c[1];
;alert(poet + " — " + street);'>run: poet + " — " + street</button><br class='clear' /></div>
<p id="long_arrow">
<b class="header">Function binding</b>
The long arrow <tt>==></tt> can be used to both define a function, and to bind
it to the current value of <tt>this</tt>, right on the spot. This is helpful
when using callback-based libraries like Prototype or jQuery, for creating
iterator functions to pass to <tt>each</tt>, or event-handler functions
to use with <tt>bind</tt>. Functions created with the long arrow are able to access
properties of the <tt>this</tt> where they're defined.
</p>
<div class='code'><pre class="idle"><span class="FunctionName">Account</span><span class="Keyword">:</span> <span class="FunctionArgument">customer, cart</span> <span class="Storage">=&gt;</span>
<span class="FunctionName">this.customer</span><span class="Keyword">:</span> customer
<span class="FunctionName">this.cart</span><span class="Keyword">:</span> cart
$(<span class="String"><span class="String">'</span>.shopping_cart<span class="String">'</span></span>).bind(<span class="String"><span class="String">'</span>click<span class="String">'</span></span>) <span class="FunctionName">event</span> <span class="Keyword">=</span><span class="Storage">=&gt;</span>
<span class="Variable">this</span>.customer.purchase(<span class="Variable">this</span>.cart)
</pre><pre class="idle"><span class="Storage">var</span> Account;
Account <span class="Keyword">=</span> <span class="Storage">function</span> <span class="FunctionName">Account</span>(<span class="FunctionArgument">customer, cart</span>) {
<span class="Storage">var</span> __a;
<span class="Variable">this</span>.customer <span class="Keyword">=</span> customer;
<span class="Variable">this</span>.cart <span class="Keyword">=</span> cart;
__a <span class="Keyword">=</span> <span class="Keyword">$</span>(<span class="String"><span class="String">'</span>.shopping_cart<span class="String">'</span></span>).bind(<span class="String"><span class="String">'</span>click<span class="String">'</span></span>, (<span class="Storage">function</span>(__this) {
<span class="Storage">var</span> <span class="FunctionName">__func</span> = <span class="Storage">function</span>(<span class="FunctionArgument">event</span>) {
<span class="Keyword">return</span> <span class="Variable">this</span>.customer.purchase(<span class="Variable">this</span>.cart);
};
<span class="Keyword">return</span> (<span class="Storage">function</span>() {
<span class="Keyword">return</span> __func.<span class="LibraryFunction">apply</span>(__this, arguments);
});
})(<span class="Variable">this</span>));
<span class="Keyword">return</span> Account <span class="Keyword">===</span> <span class="Variable">this</span>.<span class="LibraryConstant">constructor</span> ? <span class="Variable">this</span> : __a;
};
</pre><br class='clear' /></div>
<p id="embedded">
<b class="header">Embedded JavaScript</b>
Hopefully, you'll never need to use it, but if you ever need to intersperse
snippets of JavaScript within your CoffeeScript, you can
use backticks to pass it straight through.
</p>
<div class='code'><pre class="idle"><span class="FunctionName">hi</span><span class="Keyword">:</span> <span class="String"><span class="String">`</span>function() {</span>
<span class="String"> return [document.title, &quot;Hello JavaScript&quot;].join(&quot;: &quot;);</span>
<span class="String">}<span class="String">`</span></span>
</pre><pre class="idle"><span class="Storage">var</span> hi;
<span class="FunctionName">hi</span> = <span class="Storage">function</span>() {
<span class="Keyword">return</span> [<span class="LibraryClassType">document</span>.<span class="LibraryConstant">title</span>, <span class="String"><span class="String">&quot;</span>Hello JavaScript<span class="String">&quot;</span></span>].<span class="LibraryFunction">join</span>(<span class="String"><span class="String">&quot;</span>: <span class="String">&quot;</span></span>);
};
</pre><button onclick='javascript: var hi;
hi = function() {
return [document.title, "Hello JavaScript"].join(": ");
};
;alert(hi());'>run: hi()</button><br class='clear' /></div>
<p id="switch">
<b class="header">Switch/When/Else</b>
<b>Switch</b> statements in JavaScript are rather broken. You can only
do comparisons based on string equality, and need to remember to <b>break</b> at the end of
every <b>case</b> statement to avoid accidentally falling through to
the default case. CoffeeScript compiles <b>switch</b> statements into JavaScript if-else chains, allowing you to
compare any object (via <b>===</b>), preventing fall-through, and resulting
in a returnable, assignable expression. The format is: <tt>switch</tt> condition,
<tt>when</tt> clauses, <tt>else</tt> the default case.
</p>
<p>
As in Ruby, <b>switch</b> statements in CoffeeScript can take multiple
values for each <b>when</b> clause. If any of the values match, the clause
runs.
</p>
<div class='code'><pre class="idle"><span class="Keyword">switch</span> day
<span class="Keyword">when</span> <span class="String"><span class="String">&quot;</span>Mon<span class="String">&quot;</span></span> <span class="Keyword">then</span> go_to_work()
<span class="Keyword">when</span> <span class="String"><span class="String">&quot;</span>Tue<span class="String">&quot;</span></span> <span class="Keyword">then</span> go_to_the_park()
<span class="Keyword">when</span> <span class="String"><span class="String">&quot;</span>Thu<span class="String">&quot;</span></span> <span class="Keyword">then</span> go_ice_fishing()
<span class="Keyword">when</span> <span class="String"><span class="String">&quot;</span>Fri<span class="String">&quot;</span></span>, <span class="String"><span class="String">&quot;</span>Sat<span class="String">&quot;</span></span>
<span class="Keyword">if</span> day <span class="Keyword">is</span> bingo_day
go_to_bingo()
go_dancing()
<span class="Keyword">when</span> <span class="String"><span class="String">&quot;</span>Sun<span class="String">&quot;</span></span> <span class="Keyword">then</span> go_to_church()
<span class="Keyword">else</span> go_to_work()
</pre><pre class="idle"><span class="Keyword">if</span> (day <span class="Keyword">===</span> <span class="String"><span class="String">&quot;</span>Mon<span class="String">&quot;</span></span>) {
go_to_work();
} <span class="Keyword">else</span> <span class="Keyword">if</span> (day <span class="Keyword">===</span> <span class="String"><span class="String">&quot;</span>Tue<span class="String">&quot;</span></span>) {
go_to_the_park();
} <span class="Keyword">else</span> <span class="Keyword">if</span> (day <span class="Keyword">===</span> <span class="String"><span class="String">&quot;</span>Thu<span class="String">&quot;</span></span>) {
go_ice_fishing();
} <span class="Keyword">else</span> <span class="Keyword">if</span> (day <span class="Keyword">===</span> <span class="String"><span class="String">&quot;</span>Fri<span class="String">&quot;</span></span> <span class="Keyword">||</span> day <span class="Keyword">===</span> <span class="String"><span class="String">&quot;</span>Sat<span class="String">&quot;</span></span>) {
<span class="Keyword">if</span> (day <span class="Keyword">===</span> bingo_day) {
go_to_bingo();
go_dancing();
}
} <span class="Keyword">else</span> <span class="Keyword">if</span> (day <span class="Keyword">===</span> <span class="String"><span class="String">&quot;</span>Sun<span class="String">&quot;</span></span>) {
go_to_church();
} <span class="Keyword">else</span> {
go_to_work();
}
</pre><br class='clear' /></div>
<p id="try">
<b class="header">Try/Catch/Finally</b>
Try/catch statements are just about the same as JavaScript (although
they work as expressions).
</p>
<div class='code'><pre class="idle"><span class="Keyword">try</span>
all_hell_breaks_loose()
cats_and_dogs_living_together()
<span class="Keyword">catch</span> error
print(error)
<span class="Keyword">finally</span>
clean_up()
</pre><pre class="idle"><span class="Keyword">try</span> {
all_hell_breaks_loose();
cats_and_dogs_living_together();
} <span class="Keyword">catch</span> (error) {
<span class="LibraryFunction">print</span>(error);
} <span class="Keyword">finally</span> {
clean_up();
}
</pre><br class='clear' /></div>
<p id="comparisons">
<b class="header">Chained Comparisons</b>
CoffeeScript borrows
<a href="http://docs.python.org/reference/expressions.html#notin">chained comparisons</a>
from Python &mdash; making it easy to test if a value falls within a
certain range.
</p>
<div class='code'><pre class="idle"><span class="FunctionName">cholesterol</span><span class="Keyword">:</span> <span class="Number">127</span>
<span class="FunctionName">healthy</span><span class="Keyword">:</span> <span class="Number">200</span> <span class="Keyword">&gt;</span> cholesterol <span class="Keyword">&gt;</span> <span class="Number">60</span>
</pre><pre class="idle"><span class="Storage">var</span> cholesterol, healthy;
cholesterol <span class="Keyword">=</span> <span class="Number">127</span>;
healthy <span class="Keyword">=</span> (<span class="Number">200</span> <span class="Keyword">&gt;</span> cholesterol) <span class="Keyword">&amp;</span><span class="Keyword">&amp;</span> (cholesterol <span class="Keyword">&gt;</span> <span class="Number">60</span>);
</pre><button onclick='javascript: var cholesterol, healthy;
cholesterol = 127;
healthy = (200 > cholesterol) && (cholesterol > 60);
;alert(healthy);'>run: healthy</button><br class='clear' /></div>
<p id="strings">
<b class="header">Multiline Strings and Heredocs</b>
Multiline strings are allowed in CoffeeScript.
</p>
<div class='code'><pre class="idle"><span class="FunctionName">moby_dick</span><span class="Keyword">:</span> <span class="String"><span class="String">&quot;</span>Call me Ishmael. Some years ago --</span>
<span class="String">never mind how long precisely -- having little</span>
<span class="String">or no money in my purse, and nothing particular</span>
<span class="String">to interest me on shore, I thought I would sail</span>
<span class="String">about a little and see the watery part of the</span>
<span class="String">world...<span class="String">&quot;</span></span>
</pre><pre class="idle"><span class="Storage">var</span> moby_dick;
moby_dick <span class="Keyword">=</span> <span class="String"><span class="String">&quot;</span>Call me Ishmael. Some years ago -- \</span>
<span class="String">never mind how long precisely -- having little \</span>
<span class="String">or no money in my purse, and nothing particular \</span>
<span class="String">to interest me on shore, I thought I would sail \</span>
<span class="String">about a little and see the watery part of the \</span>
<span class="String">world...<span class="String">&quot;</span></span>;
</pre><button onclick='javascript: var moby_dick;
moby_dick = "Call me Ishmael. Some years ago -- \
never mind how long precisely -- having little \
or no money in my purse, and nothing particular \
to interest me on shore, I thought I would sail \
about a little and see the watery part of the \
world...";
;alert(moby_dick);'>run: moby_dick</button><br class='clear' /></div>
<p>
Heredocs can be used to hold formatted or indentation-sensitive text
(or, if you just don't feel like escaping quotes and apostrophes). The
indentation level that begins the heredoc is maintained throughout, so
you can keep it all aligned with the body of your code.
</p>
<div class='code'><pre class="idle"><span class="FunctionName">html</span><span class="Keyword">:</span> <span class="String"><span class="String">'</span><span class="String">'</span></span><span class="String"><span class="String">'</span></span>
<span class="String"> &lt;strong&gt;</span>
<span class="String"> cup of coffeescript</span>
<span class="String"> &lt;/strong&gt;</span>
<span class="String"> <span class="String">'</span></span><span class="String"><span class="String">'</span><span class="String">'</span></span>
</pre><pre class="idle"><span class="Storage">var</span> html;
html <span class="Keyword">=</span> <span class="String"><span class="String">&quot;</span>&lt;strong&gt;<span class="UserDefinedConstant">\n</span> cup of coffeescript<span class="UserDefinedConstant">\n</span>&lt;/strong&gt;<span class="String">&quot;</span></span>;
</pre><br class='clear' /></div>
<h2 id="resources">Resources</h2>
<ul>
<li>
<a href="http://github.com/jashkenas/coffee-script/">Source Code</a><br />
After checking out the source, make sure to run <tt>rake build:parser</tt>
to generate an up-to-date version of the Racc parser.
Use <tt>bin/coffee</tt> to test your changes,
<tt>rake test</tt> to run the test suite,
and <tt>rake gem:install</tt> to
create and install a custom version of the gem.
</li>
<li>
<a href="http://github.com/jashkenas/coffee-script/issues">Bugs, Feature Requests, and General Discussion</a>
</li>
<li>
<a href="http://github.com/jnicklas/bistro_car">BistroCar</a><br />
A Rails plugin by
<a href="http://github.com/jnicklas">Jonas Nicklas</a>
that includes CoffeeScript helpers,
bundling and minification.
</li>
<li>
<a href="http://github.com/inem/coffee-haml-filter">coffee-haml-filter</a><br />
A custom <a href="http://haml-lang.com/">HAML</a> filter, by
<a href="http://github.com/inem">Ivan Nemytchenko</a>, that embeds
snippets of CoffeeScript within your HAML templates.
</li>
</ul>
<h2 id="contributing">Contributing</h2>
<p>
Here's a wish list of things that would be wonderful to have contributed:
</p>
<ul>
<li>
<a href="http://github.com/jashkenas/coffee-script/issues#issue/8">
A CoffeeScript version of the compiler.
</a>
</li>
<li>
Test cases for any syntax errors you encounter that you think CoffeeScript
should be able to compile properly.
</li>
<li>
A tutorial that introduces CoffeeScript from the ground up for folks
without knowledge of JavaScript.
</li>
<li>
Integration with Processing.js's JavaScript API (this would depend on
having a JavaScript version of the compiler).
</li>
<li>
A lot of the code generation in <tt>nodes.rb</tt> gets into messy
string manipulation. Techniques for cleaning this up across the board
would be appreciated.
</li>
</ul>
<h2 id="change_log">Change Log</h2>
<p>
<b class="header" style="margin-top: 20px;">0.2.6</b>
Added Python-style chained comparisons, the conditional existence
operator <tt>?=</tt>, and some examples from <i>Beautiful Code</i>.
Bugfixes relating to statement-to-expression conversion, arguments-to-array
conversion, and the TextMate syntax highlighter.
</p>
<p>
<b class="header" style="margin-top: 20px;">0.2.5</b>
The conditions in switch statements can now take multiple values at once &mdash;
If any of them are true, the case will run. Added the long arrow <tt>==></tt>,
which defines and immediately binds a function to <tt>this</tt>. While loops can
now be used as expressions, in the same way that comprehensions can. Splats
can be used within pattern matches to soak up the rest of an array.
</p>
<p>
<b class="header" style="margin-top: 20px;">0.2.4</b>
Added ECMAScript Harmony style destructuring assignment, for dealing with
extracting values from nested arrays and objects. Added indentation-sensitive
heredocs for nicely formatted strings or chunks of code.
</p>
<p>
<b class="header" style="margin-top: 20px;">0.2.3</b>
Axed the unsatisfactory <tt>ino</tt> keyword, replacing it with <tt>of</tt> for
object comprehensions. They now look like: <tt>for prop, value of object</tt>.
</p>
<p>
<b class="header" style="margin-top: 20px;">0.2.2</b>
When performing a comprehension over an object, use <tt>ino</tt>, instead
of <tt>in</tt>, which helps us generate smaller, more efficient code at
compile time.
<br />
Added <tt>::</tt> as a shorthand for saying <tt>.prototype.</tt>
<br />
The "splat" symbol has been changed from a prefix asterisk <tt>*</tt>, to
a postfix ellipsis <tt>...</tt>
<br />
Added JavaScript's <tt>in</tt> operator,
empty <tt>return</tt> statements, and empty <tt>while</tt> loops.
<br />
Constructor functions that start with capital letters now include a
safety check to make sure that the new instance of the object is returned.
<br />
The <tt>extends</tt> keyword now functions identically to <tt>goog.inherits</tt>
in Google's Closure Library.
</p>
<p>
<b class="header" style="margin-top: 20px;">0.2.1</b>
Arguments objects are now converted into real arrays when referenced.
</p>
<p>
<b class="header" style="margin-top: 20px;">0.2.0</b>
Major release. Significant whitespace. Better statement-to-expression
conversion. Splats. Splice literals. Object comprehensions. Blocks.
The existential operator. Many thanks to all the folks who posted issues,
with special thanks to
<a href="http://github.com/kamatsu">Liam O'Connor-Davis</a> for whitespace
and expression help.
</p>
<p>
<b class="header" style="margin-top: 20px;">0.1.6</b>
Bugfix for running <tt>coffee --interactive</tt> and <tt>--run</tt>
from outside of the CoffeeScript directory. Bugfix for nested
function/if-statements.
</p>
<p>
<b class="header" style="margin-top: 20px;">0.1.5</b>
Array slice literals and array comprehensions can now both take Ruby-style
ranges to specify the start and end. JavaScript variable declaration is
now pushed up to the top of the scope, making all assignment statements into
expressions. You can use <tt>\</tt> to escape newlines.
The <tt>coffee-script</tt> command is now called <tt>coffee</tt>.
</p>
<p>
<b class="header" style="margin-top: 20px;">0.1.4</b>
The official CoffeeScript extension is now <tt>.coffee</tt> instead of
<tt>.cs</tt>, which properly belongs to
<a href="http://en.wikipedia.org/wiki/C_Sharp_(programming_language)">C#</a>.
Due to popular demand, you can now also use <tt>=</tt> to assign. Unlike
JavaScript, <tt>=</tt> can also be used within object literals, interchangeably
with <tt>:</tt>. Made a grammatical fix for chained function calls
like <tt>func(1)(2)(3)(4)</tt>. Inheritance and super no longer use
<tt>__proto__</tt>, so they should be IE-compatible now.
</p>
<p>
<b class="header" style="margin-top: 20px;">0.1.3</b>
The <tt>coffee</tt> command now includes <tt>--interactive</tt>,
which launches an interactive CoffeeScript session, and <tt>--run</tt>,
which directly compiles and executes a script. Both options depend on a
working installation of Narwhal.
The <tt>aint</tt> keyword has been replaced by <tt>isnt</tt>, which goes
together a little smoother with <tt>is</tt>.
Quoted strings are now allowed as identifiers within object literals: eg.
<tt>{"5+5": 10}</tt>.
All assignment operators now use a colon: <tt>+:</tt>, <tt>-:</tt>,
<tt>*:</tt>, etc.
</p>
<p>
<b class="header" style="margin-top: 20px;">0.1.2</b>
Fixed a bug with calling <tt>super()</tt> through more than one level of
inheritance, with the re-addition of the <tt>extends</tt> keyword.
Added experimental <a href="http://narwhaljs.org/">Narwhal</a>
support (as a Tusk package), contributed by
<a href="http://tlrobinson.net/">Tom Robinson</a>, including
<b>bin/cs</b> as a CoffeeScript REPL and interpreter.
New <tt>--no-wrap</tt> option to suppress the safety function
wrapper.
</p>
<p>
<b class="header" style="margin-top: 20px;">0.1.1</b>
Added <tt>instanceof</tt> and <tt>typeof</tt> as operators.
</p>
<p>
<b class="header" style="margin-top: 20px;">0.1.0</b>
Initial CoffeeScript release.
</p>
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