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<!DOCTYPE HTML>
<html>
<head>
<meta http-equiv="content-type" content="text/html;charset=UTF-8" />
<meta http-equiv="X-UA-Compatible" content="chrome=1" />
<meta name="viewport" content="width=device-width" />
<link rel="canonical" href="http://underscorejs.org" />
<link rel="shortcut icon" href="favicon.ico" type="image/x-icon" />
<title>Underscore.js</title>
<style>
body {
font-size: 14px;
line-height: 22px;
background: #f4f4f4 url(docs/images/background.png);
color: #000;
font-family: Helvetica Neue, Helvetica, Arial;
}
.interface {
font-family: "Lucida Grande", "Lucida Sans Unicode", Helvetica, Arial, sans-serif !important;
}
div#sidebar {
background: #fff;
position: fixed;
top: 0; left: 0; bottom: 0;
width: 200px;
overflow-y: auto;
overflow-x: hidden;
-webkit-overflow-scrolling: touch;
padding: 15px 0 30px 30px;
border-right: 1px solid #bbb;
box-shadow: 0 0 20px #ccc; -webkit-box-shadow: 0 0 20px #ccc; -moz-box-shadow: 0 0 20px #ccc;
}
a.toc_title, a.toc_title:visited {
display: block;
color: black;
font-weight: bold;
margin-top: 15px;
}
a.toc_title:hover {
text-decoration: underline;
}
#sidebar .version {
font-size: 10px;
font-weight: normal;
}
ul.toc_section {
font-size: 11px;
line-height: 14px;
margin: 5px 0 0 0;
padding-left: 0px;
list-style-type: none;
font-family: Lucida Grande;
}
.toc_section li {
cursor: pointer;
margin: 0 0 3px 0;
}
.toc_section li a {
text-decoration: none;
color: black;
}
.toc_section li a:hover {
text-decoration: underline;
}
div.container {
width: 550px;
margin: 40px 0 50px 260px;
}
img#logo {
width: 396px;
height: 69px;
}
div.warning {
margin-top: 15px;
font: bold 11px Arial;
color: #770000;
}
p {
margin: 20px 0;
width: 550px;
}
a, a:visited {
color: #444;
}
a:active, a:hover {
color: #000;
}
h1, h2, h3, h4, h5, h6 {
padding-top: 20px;
}
h2 {
font-size: 20px;
}
b.header {
font-size: 16px;
line-height: 30px;
}
span.alias {
font-size: 14px;
font-style: italic;
margin-left: 20px;
}
table, tr, td {
margin: 0; padding: 0;
}
td {
padding: 2px 12px 2px 0;
}
ul {
list-style-type: circle;
padding: 0 0 0 20px;
}
li {
width: 500px;
margin-bottom: 10px;
}
code, pre, tt {
font-family: Monaco, Consolas, "Lucida Console", monospace;
font-size: 12px;
line-height: 18px;
font-style: normal;
}
tt {
padding: 0px 3px;
background: #fff;
border: 1px solid #ddd;
zoom: 1;
}
code {
margin-left: 20px;
}
pre {
font-size: 12px;
padding: 2px 0 2px 15px;
border-left: 5px solid #bbb;
margin: 0px 0 30px;
}
@media only screen and (-webkit-min-device-pixel-ratio: 1.5) and (max-width: 640px),
only screen and (-o-min-device-pixel-ratio: 3/2) and (max-width: 640px),
only screen and (min-device-pixel-ratio: 1.5) and (max-width: 640px) {
img {
max-width: 100%;
}
div#sidebar {
-webkit-overflow-scrolling: initial;
position: relative;
width: 90%;
height: 120px;
left: 0;
top: -7px;
padding: 10px 0 10px 30px;
border: 0;
}
img#logo {
width: auto;
height: auto;
}
div.container {
margin: 0;
width: 100%;
}
p, div.container ul {
max-width: 98%;
overflow-x: scroll;
}
pre {
overflow: scroll;
}
}
</style>
</head>
<body>
<div id="sidebar" class="interface">
<a class="toc_title" href="#">
Underscore.js <span class="version">(1.3.3)</span>
</a>
<a class="toc_title" href="#">
Introduction
</a>
<a class="toc_title" href="#collections">
Collections
</a>
<ul class="toc_section">
<li>- <a href="#each">each</a></li>
<li>- <a href="#map">map</a></li>
<li>- <a href="#reduce">reduce</a></li>
<li>- <a href="#reduceRight">reduceRight</a></li>
<li>- <a href="#find">find</a></li>
<li>- <a href="#filter">filter</a></li>
<li>- <a href="#reject">reject</a></li>
<li>- <a href="#all">all</a></li>
<li>- <a href="#any">any</a></li>
<li>- <a href="#include">include</a></li>
<li>- <a href="#invoke">invoke</a></li>
<li>- <a href="#pluck">pluck</a></li>
<li>- <a href="#max">max</a></li>
<li>- <a href="#min">min</a></li>
<li>- <a href="#sortBy">sortBy</a></li>
<li>- <a href="#groupBy">groupBy</a></li>
<li>- <a href="#shuffle">shuffle</a></li>
<li>- <a href="#toArray">toArray</a></li>
<li>- <a href="#size">size</a></li>
</ul>
<a class="toc_title" href="#arrays">
Arrays
</a>
<ul class="toc_section">
<li>- <a href="#first">first</a></li>
<li>- <a href="#initial">initial</a></li>
<li>- <a href="#last">last</a></li>
<li>- <a href="#rest">rest</a></li>
<li>- <a href="#compact">compact</a></li>
<li>- <a href="#flatten">flatten</a></li>
<li>- <a href="#without">without</a></li>
<li>- <a href="#union">union</a></li>
<li>- <a href="#intersection">intersection</a></li>
<li>- <a href="#difference">difference</a></li>
<li>- <a href="#uniq">uniq</a></li>
<li>- <a href="#zip">zip</a></li>
<li>- <a href="#indexOf">indexOf</a></li>
<li>- <a href="#lastIndexOf">lastIndexOf</a></li>
<li>- <a href="#sortedIndex">sortedIndex</a></li>
<li>- <a href="#range">range</a></li>
</ul>
<a class="toc_title" href="#functions">
Functions
</a>
<ul class="toc_section">
<li>- <a href="#bind">bind</a></li>
<li>- <a href="#bindAll">bindAll</a></li>
<li>- <a href="#memoize">memoize</a></li>
<li>- <a href="#delay">delay</a></li>
<li>- <a href="#defer">defer</a></li>
<li>- <a href="#throttle">throttle</a></li>
<li>- <a href="#debounce">debounce</a></li>
<li>- <a href="#once">once</a></li>
<li>- <a href="#after">after</a></li>
<li>- <a href="#wrap">wrap</a></li>
<li>- <a href="#compose">compose</a></li>
</ul>
<a class="toc_title" href="#objects">
Objects
</a>
<ul class="toc_section">
<li>- <a href="#keys">keys</a></li>
<li>- <a href="#values">values</a></li>
<li>- <a href="#object-functions">functions</a></li>
<li>- <a href="#extend">extend</a></li>
<li>- <a href="#pick">pick</a></li>
<li>- <a href="#omit">omit</a></li>
<li>- <a href="#defaults">defaults</a></li>
<li>- <a href="#clone">clone</a></li>
<li>- <a href="#tap">tap</a></li>
<li>- <a href="#has">has</a></li>
<li>- <a href="#isEqual">isEqual</a></li>
<li>- <a href="#isEmpty">isEmpty</a></li>
<li>- <a href="#isElement">isElement</a></li>
<li>- <a href="#isArray">isArray</a></li>
<li>- <a href="#isObject">isObject</a></li>
<li>- <a href="#isArguments">isArguments</a></li>
<li>- <a href="#isFunction">isFunction</a></li>
<li>- <a href="#isString">isString</a></li>
<li>- <a href="#isNumber">isNumber</a></li>
<li>- <a href="#isFinite">isFinite</a></li>
<li>- <a href="#isBoolean">isBoolean</a></li>
<li>- <a href="#isDate">isDate</a></li>
<li>- <a href="#isRegExp">isRegExp</a></li>
<li>- <a href="#isNaN">isNaN</a></li>
<li>- <a href="#isNull">isNull</a></li>
<li>- <a href="#isUndefined">isUndefined</a></li>
</ul>
<a class="toc_title" href="#utility">
Utility
</a>
<ul class="toc_section">
<li>- <a href="#noConflict">noConflict</a></li>
<li>- <a href="#identity">identity</a></li>
<li>- <a href="#times">times</a></li>
<li>- <a href="#mixin">mixin</a></li>
<li>- <a href="#uniqueId">uniqueId</a></li>
<li>- <a href="#escape">escape</a></li>
<li>- <a href="#result">result</a></li>
<li>- <a href="#template">template</a></li>
</ul>
<a class="toc_title" href="#chaining">
Chaining
</a>
<ul class="toc_section">
<li>- <a href="#chain">chain</a></li>
<li>- <a href="#value">value</a></li>
</ul>
<a class="toc_title" href="#links">
Links
</a>
<a class="toc_title" href="#changelog">
Change Log
</a>
</div>
<div class="container">
<p id="introduction">
<img id="logo" src="docs/images/underscore.png" alt="Underscore.js" />
</p>
<p>
<a href="http://github.com/documentcloud/underscore/">Underscore</a> is a
utility-belt library for JavaScript that provides a lot of the
functional programming support that you would expect in
<a href="http://prototypejs.org/api">Prototype.js</a>
(or <a href="http://www.ruby-doc.org/core/classes/Enumerable.html">Ruby</a>),
but without extending any of the built-in JavaScript objects. It's the
tie to go along with <a href="http://docs.jquery.com">jQuery</a>'s tux,
and <a href="http://backbonejs.org">Backbone.js</a>'s suspenders.
</p>
<p>
Underscore provides 80-odd functions that support both the usual
functional suspects: <b>map</b>, <b>select</b>, <b>invoke</b> —
as well as more specialized helpers: function binding, javascript
templating, deep equality testing, and so on. It delegates to built-in
functions, if present, so modern browsers will use the
native implementations of <b>forEach</b>, <b>map</b>, <b>reduce</b>,
<b>filter</b>, <b>every</b>, <b>some</b> and <b>indexOf</b>.
</p>
<p>
A complete <a href="test/">Test & Benchmark Suite</a>
is included for your perusal.
</p>
<p>
You may also read through the <a href="docs/underscore.html">annotated source code</a>.
</p>
<p>
The project is
<a href="http://github.com/documentcloud/underscore/">hosted on GitHub</a>.
You can report bugs and discuss features on the
<a href="http://github.com/documentcloud/underscore/issues">issues page</a>,
on Freenode in the <tt>#documentcloud</tt> channel,
or send tweets to <a href="http://twitter.com/documentcloud">@documentcloud</a>.
</p>
<p>
<i>Underscore is an open-source component of <a href="http://documentcloud.org/">DocumentCloud</a>.</i>
</p>
<h2>Downloads <i style="padding-left: 12px; font-size:12px;">(Right-click, and use "Save As")</i></h2>
<table>
<tr>
<td><a href="underscore.js">Development Version (1.3.3)</a></td>
<td><i>37kb, Uncompressed with Plentiful Comments</i></td>
</tr>
<tr>
<td><a href="underscore-min.js">Production Version (1.3.3)</a></td>
<td><i>4kb, Minified and Gzipped</i></td>
</tr>
</table>
<div id="documentation">
<h2 id="collections">Collection Functions (Arrays or Objects)</h2>
<p id="each">
<b class="header">each</b><code>_.each(list, iterator, [context])</code>
<span class="alias">Alias: <b>forEach</b></span>
<br />
Iterates over a <b>list</b> of elements, yielding each in turn to an <b>iterator</b>
function. The <b>iterator</b> is bound to the <b>context</b> object, if one is
passed. Each invocation of <b>iterator</b> is called with three arguments:
<tt>(element, index, list)</tt>. If <b>list</b> is a JavaScript object, <b>iterator</b>'s
arguments will be <tt>(value, key, list)</tt>. Delegates to the native
<b>forEach</b> function if it exists.
</p>
<pre>
_.each([1, 2, 3], function(num){ alert(num); });
=> alerts each number in turn...
_.each({one : 1, two : 2, three : 3}, function(num, key){ alert(num); });
=> alerts each number in turn...</pre>
<p id="map">
<b class="header">map</b><code>_.map(list, iterator, [context])</code>
<span class="alias">Alias: <b>collect</b></span>
<br />
Produces a new array of values by mapping each value in <b>list</b>
through a transformation function (<b>iterator</b>). If the native <b>map</b> method
exists, it will be used instead. If <b>list</b> is a JavaScript object,
<b>iterator</b>'s arguments will be <tt>(value, key, list)</tt>.
</p>
<pre>
_.map([1, 2, 3], function(num){ return num * 3; });
=> [3, 6, 9]
_.map({one : 1, two : 2, three : 3}, function(num, key){ return num * 3; });
=> [3, 6, 9]</pre>
<p id="reduce">
<b class="header">reduce</b><code>_.reduce(list, iterator, memo, [context])</code>
<span class="alias">Aliases: <b>inject, foldl</b></span>
<br />
Also known as <b>inject</b> and <b>foldl</b>, <b>reduce</b> boils down a
<b>list</b> of values into a single value. <b>Memo</b> is the initial state
of the reduction, and each successive step of it should be returned by
<b>iterator</b>. The iterator is passed four arguments: the <tt>memo</tt>,
then the <tt>value</tt> and <tt>index</tt> (or key) of the iteration,
and finally a reference to the entire <tt>list</tt>.
</p>
<pre>
var sum = _.reduce([1, 2, 3], function(memo, num){ return memo + num; }, 0);
=> 6
</pre>
<p id="reduceRight">
<b class="header">reduceRight</b><code>_.reduceRight(list, iterator, memo, [context])</code>
<span class="alias">Alias: <b>foldr</b></span>
<br />
The right-associative version of <b>reduce</b>. Delegates to the
JavaScript 1.8 version of <b>reduceRight</b>, if it exists. <b>Foldr</b>
is not as useful in JavaScript as it would be in a language with lazy
evaluation.
</p>
<pre>
var list = [[0, 1], [2, 3], [4, 5]];
var flat = _.reduceRight(list, function(a, b) { return a.concat(b); }, []);
=> [4, 5, 2, 3, 0, 1]
</pre>
<p id="find">
<b class="header">find</b><code>_.find(list, iterator, [context])</code>
<span class="alias">Alias: <b>detect</b></span>
<br />
Looks through each value in the <b>list</b>, returning the first one that
passes a truth test (<b>iterator</b>). The function returns as
soon as it finds an acceptable element, and doesn't traverse the
entire list.
</p>
<pre>
var even = _.find([1, 2, 3, 4, 5, 6], function(num){ return num % 2 == 0; });
=> 2
</pre>
<p id="filter">
<b class="header">filter</b><code>_.filter(list, iterator, [context])</code>
<span class="alias">Alias: <b>select</b></span>
<br />
Looks through each value in the <b>list</b>, returning an array of all
the values that pass a truth test (<b>iterator</b>). Delegates to the
native <b>filter</b> method, if it exists.
</p>
<pre>
var evens = _.filter([1, 2, 3, 4, 5, 6], function(num){ return num % 2 == 0; });
=> [2, 4, 6]
</pre>
<p id="reject">
<b class="header">reject</b><code>_.reject(list, iterator, [context])</code>
<br />
Returns the values in <b>list</b> without the elements that the truth
test (<b>iterator</b>) passes. The opposite of <b>filter</b>.
</p>
<pre>
var odds = _.reject([1, 2, 3, 4, 5, 6], function(num){ return num % 2 == 0; });
=> [1, 3, 5]
</pre>
<p id="all">
<b class="header">all</b><code>_.all(list, iterator, [context])</code>
<span class="alias">Alias: <b>every</b></span>
<br />
Returns <i>true</i> if all of the values in the <b>list</b> pass the <b>iterator</b>
truth test. Delegates to the native method <b>every</b>, if present.
</p>
<pre>
_.all([true, 1, null, 'yes'], _.identity);
=> false
</pre>
<p id="any">
<b class="header">any</b><code>_.any(list, [iterator], [context])</code>
<span class="alias">Alias: <b>some</b></span>
<br />
Returns <i>true</i> if any of the values in the <b>list</b> pass the
<b>iterator</b> truth test. Short-circuits and stops traversing the list
if a true element is found. Delegates to the native method <b>some</b>,
if present.
</p>
<pre>
_.any([null, 0, 'yes', false]);
=> true
</pre>
<p id="include">
<b class="header">include</b><code>_.include(list, value)</code>
<span class="alias">Alias: <b>contains</b></span>
<br />
Returns <i>true</i> if the <b>value</b> is present in the <b>list</b>.
Uses <b>indexOf</b> internally, if <b>list</b> is an Array.
</p>
<pre>
_.include([1, 2, 3], 3);
=> true
</pre>
<p id="invoke">
<b class="header">invoke</b><code>_.invoke(list, methodName, [*arguments])</code>
<br />
Calls the method named by <b>methodName</b> on each value in the <b>list</b>.
Any extra arguments passed to <b>invoke</b> will be forwarded on to the
method invocation.
</p>
<pre>
_.invoke([[5, 1, 7], [3, 2, 1]], 'sort');
=> [[1, 5, 7], [1, 2, 3]]
</pre>
<p id="pluck">
<b class="header">pluck</b><code>_.pluck(list, propertyName)</code>
<br />
A convenient version of what is perhaps the most common use-case for
<b>map</b>: extracting a list of property values.
</p>
<pre>
var stooges = [{name : 'moe', age : 40}, {name : 'larry', age : 50}, {name : 'curly', age : 60}];
_.pluck(stooges, 'name');
=> ["moe", "larry", "curly"]
</pre>
<p id="max">
<b class="header">max</b><code>_.max(list, [iterator], [context])</code>
<br />
Returns the maximum value in <b>list</b>. If <b>iterator</b> is passed,
it will be used on each value to generate the criterion by which the
value is ranked.
</p>
<pre>
var stooges = [{name : 'moe', age : 40}, {name : 'larry', age : 50}, {name : 'curly', age : 60}];
_.max(stooges, function(stooge){ return stooge.age; });
=> {name : 'curly', age : 60};
</pre>
<p id="min">
<b class="header">min</b><code>_.min(list, [iterator], [context])</code>
<br />
Returns the minimum value in <b>list</b>. If <b>iterator</b> is passed,
it will be used on each value to generate the criterion by which the
value is ranked.
</p>
<pre>
var numbers = [10, 5, 100, 2, 1000];
_.min(numbers);
=> 2
</pre>
<p id="sortBy">
<b class="header">sortBy</b><code>_.sortBy(list, iterator, [context])</code>
<br />
Returns a sorted copy of <b>list</b>, ranked in ascending order by the
results of running each value through <b>iterator</b>. Iterator may
also be the string name of the property to sort by (eg. <tt>length</tt>).
</p>
<pre>
_.sortBy([1, 2, 3, 4, 5, 6], function(num){ return Math.sin(num); });
=> [5, 4, 6, 3, 1, 2]
</pre>
<p id="groupBy">
<b class="header">groupBy</b><code>_.groupBy(list, iterator)</code>
<br />
Splits a collection into sets, grouped by the result of running each
value through <b>iterator</b>. If <b>iterator</b> is a string instead of
a function, groups by the property named by <b>iterator</b> on each of
the values.
</p>
<pre>
_.groupBy([1.3, 2.1, 2.4], function(num){ return Math.floor(num); });
=> {1: [1.3], 2: [2.1, 2.4]}
_.groupBy(['one', 'two', 'three'], 'length');
=> {3: ["one", "two"], 5: ["three"]}
</pre>
<p id="shuffle">
<b class="header">shuffle</b><code>_.shuffle(list)</code>
<br />
Returns a shuffled copy of the <b>list</b>, using a version of the
<a href="http://en.wikipedia.org/wiki/Fisher%E2%80%93Yates_shuffle">Fisher-Yates shuffle</a>.
</p>
<pre>
_.shuffle([1, 2, 3, 4, 5, 6]);
=> [4, 1, 6, 3, 5, 2]
</pre>
<p id="toArray">
<b class="header">toArray</b><code>_.toArray(list)</code>
<br />
Converts the <b>list</b> (anything that can be iterated over), into a
real Array. Useful for transmuting the <b>arguments</b> object.
</p>
<pre>
(function(){ return _.toArray(arguments).slice(1); })(1, 2, 3, 4);
=> [2, 3, 4]
</pre>
<p id="size">
<b class="header">size</b><code>_.size(list)</code>
<br />
Return the number of values in the <b>list</b>.
</p>
<pre>
_.size({one : 1, two : 2, three : 3});
=> 3
</pre>
<h2 id="arrays">Array Functions</h2>
<p>
<i>
Note: All array functions will also work on the <b>arguments</b> object.
However, Underscore functions are not designed to work on "sparse" arrays.
</i>
</p>
<p id="first">
<b class="header">first</b><code>_.first(array, [n])</code>
<span class="alias">Alias: <b>head</b>, <b>take</b></span>
<br />
Returns the first element of an <b>array</b>. Passing <b>n</b> will
return the first <b>n</b> elements of the array.
</p>
<pre>
_.first([5, 4, 3, 2, 1]);
=> 5
</pre>
<p id="initial">
<b class="header">initial</b><code>_.initial(array, [n])</code>
<br />
Returns everything but the last entry of the array. Especially useful on
the arguments object. Pass <b>n</b> to exclude the last <b>n</b> elements
from the result.
</p>
<pre>
_.initial([5, 4, 3, 2, 1]);
=> [5, 4, 3, 2]
</pre>
<p id="last">
<b class="header">last</b><code>_.last(array, [n])</code>
<br />
Returns the last element of an <b>array</b>. Passing <b>n</b> will return
the last <b>n</b> elements of the array.
</p>
<pre>
_.last([5, 4, 3, 2, 1]);
=> 1
</pre>
<p id="rest">
<b class="header">rest</b><code>_.rest(array, [index])</code>
<span class="alias">Alias: <b>tail, drop</b></span>
<br />
Returns the <b>rest</b> of the elements in an array. Pass an <b>index</b>
to return the values of the array from that index onward.
</p>
<pre>
_.rest([5, 4, 3, 2, 1]);
=> [4, 3, 2, 1]
</pre>
<p id="compact">
<b class="header">compact</b><code>_.compact(array)</code>
<br />
Returns a copy of the <b>array</b> with all falsy values removed.
In JavaScript, <i>false</i>, <i>null</i>, <i>0</i>, <i>""</i>,
<i>undefined</i> and <i>NaN</i> are all falsy.
</p>
<pre>
_.compact([0, 1, false, 2, '', 3]);
=> [1, 2, 3]
</pre>
<p id="flatten">
<b class="header">flatten</b><code>_.flatten(array, [shallow])</code>
<br />
Flattens a nested <b>array</b> (the nesting can be to any depth). If you
pass <b>shallow</b>, the array will only be flattened a single level.
</p>
<pre>
_.flatten([1, [2], [3, [[4]]]]);
=> [1, 2, 3, 4];
_.flatten([1, [2], [3, [[4]]]], true);
=> [1, 2, 3, [[4]]];
</pre>
<p id="without">
<b class="header">without</b><code>_.without(array, [*values])</code>
<br />
Returns a copy of the <b>array</b> with all instances of the <b>values</b>
removed.
</p>
<pre>
_.without([1, 2, 1, 0, 3, 1, 4], 0, 1);
=> [2, 3, 4]
</pre>
<p id="union">
<b class="header">union</b><code>_.union(*arrays)</code>
<br />
Computes the union of the passed-in <b>arrays</b>: the list of unique items,
in order, that are present in one or more of the <b>arrays</b>.
</p>
<pre>
_.union([1, 2, 3], [101, 2, 1, 10], [2, 1]);
=> [1, 2, 3, 101, 10]
</pre>
<p id="intersection">
<b class="header">intersection</b><code>_.intersection(*arrays)</code>
<br />
Computes the list of values that are the intersection of all the <b>arrays</b>.
Each value in the result is present in each of the <b>arrays</b>.
</p>
<pre>
_.intersection([1, 2, 3], [101, 2, 1, 10], [2, 1]);
=> [1, 2]
</pre>
<p id="difference">
<b class="header">difference</b><code>_.difference(array, *others)</code>
<br />
Similar to <b>without</b>, but returns the values from <b>array</b> that
are not present in the <b>other</b> arrays.
</p>
<pre>
_.difference([1, 2, 3, 4, 5], [5, 2, 10]);
=> [1, 3, 4]
</pre>
<p id="uniq">
<b class="header">uniq</b><code>_.uniq(array, [isSorted], [iterator])</code>
<span class="alias">Alias: <b>unique</b></span>
<br />
Produces a duplicate-free version of the <b>array</b>, using <i>===</i> to test
object equality. If you know in advance that the <b>array</b> is sorted,
passing <i>true</i> for <b>isSorted</b> will run a much faster algorithm.
If you want to compute unique items based on a transformation, pass an
<b>iterator</b> function.
</p>
<pre>
_.uniq([1, 2, 1, 3, 1, 4]);
=> [1, 2, 3, 4]
</pre>
<p id="zip">
<b class="header">zip</b><code>_.zip(*arrays)</code>
<br />
Merges together the values of each of the <b>arrays</b> with the
values at the corresponding position. Useful when you have separate
data sources that are coordinated through matching array indexes.
If you're working with a matrix of nested arrays, <b>zip.apply</b>
can transpose the matrix in a similar fashion.
</p>
<pre>
_.zip(['moe', 'larry', 'curly'], [30, 40, 50], [true, false, false]);
=> [["moe", 30, true], ["larry", 40, false], ["curly", 50, false]]
</pre>
<p id="indexOf">
<b class="header">indexOf</b><code>_.indexOf(array, value, [isSorted])</code>
<br />
Returns the index at which <b>value</b> can be found in the <b>array</b>,
or <i>-1</i> if value is not present in the <b>array</b>. Uses the native
<b>indexOf</b> function unless it's missing. If you're working with a
large array, and you know that the array is already sorted, pass <tt>true</tt>
for <b>isSorted</b> to use a faster binary search.
</p>
<pre>
_.indexOf([1, 2, 3], 2);
=> 1
</pre>
<p id="lastIndexOf">
<b class="header">lastIndexOf</b><code>_.lastIndexOf(array, value)</code>
<br />
Returns the index of the last occurrence of <b>value</b> in the <b>array</b>,
or <i>-1</i> if value is not present. Uses the native <b>lastIndexOf</b>
function if possible.
</p>
<pre>
_.lastIndexOf([1, 2, 3, 1, 2, 3], 2);
=> 4
</pre>
<p id="sortedIndex">
<b class="header">sortedIndex</b><code>_.sortedIndex(list, value, [iterator])</code>
<br />
Uses a binary search to determine the index at which the <b>value</b>
<i>should</i> be inserted into the <b>list</b> in order to maintain the <b>list</b>'s
sorted order. If an <b>iterator</b> is passed, it will be used to compute
the sort ranking of each value.
</p>
<pre>
_.sortedIndex([10, 20, 30, 40, 50], 35);
=> 3
</pre>
<p id="range">
<b class="header">range</b><code>_.range([start], stop, [step])</code>
<br />
A function to create flexibly-numbered lists of integers, handy for
<tt>each</tt> and <tt>map</tt> loops. <b>start</b>, if omitted, defaults
to <i>0</i>; <b>step</b> defaults to <i>1</i>. Returns a list of integers
from <b>start</b> to <b>stop</b>, incremented (or decremented) by <b>step</b>,
exclusive.
</p>
<pre>
_.range(10);
=> [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
_.range(1, 11);
=> [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
_.range(0, 30, 5);
=> [0, 5, 10, 15, 20, 25]
_.range(0, -10, -1);
=> [0, -1, -2, -3, -4, -5, -6, -7, -8, -9]
_.range(0);
=> []
</pre>
<h2 id="functions">Function (uh, ahem) Functions</h2>
<p id="bind">
<b class="header">bind</b><code>_.bind(function, object, [*arguments])</code>
<br />
Bind a <b>function</b> to an <b>object</b>, meaning that whenever
the function is called, the value of <i>this</i> will be the <b>object</b>.
Optionally, bind <b>arguments</b> to the <b>function</b> to pre-fill them,
also known as <b>partial application</b>.
</p>
<pre>
var func = function(greeting){ return greeting + ': ' + this.name };
func = _.bind(func, {name : 'moe'}, 'hi');
func();
=> 'hi: moe'
</pre>
<p id="bindAll">
<b class="header">bindAll</b><code>_.bindAll(object, [*methodNames])</code>
<br />
Binds a number of methods on the <b>object</b>, specified by
<b>methodNames</b>, to be run in the context of that object whenever they
are invoked. Very handy for binding functions that are going to be used
as event handlers, which would otherwise be invoked with a fairly useless
<i>this</i>. If no <b>methodNames</b> are provided, all of the object's
function properties will be bound to it.
</p>
<pre>
var buttonView = {
label : 'underscore',
onClick : function(){ alert('clicked: ' + this.label); },
onHover : function(){ console.log('hovering: ' + this.label); }
};
_.bindAll(buttonView);
jQuery('#underscore_button').bind('click', buttonView.onClick);
=> When the button is clicked, this.label will have the correct value...
</pre>
<p id="memoize">
<b class="header">memoize</b><code>_.memoize(function, [hashFunction])</code>
<br />
Memoizes a given <b>function</b> by caching the computed result. Useful
for speeding up slow-running computations. If passed an optional
<b>hashFunction</b>, it will be used to compute the hash key for storing
the result, based on the arguments to the original function. The default
<b>hashFunction</b> just uses the first argument to the memoized function
as the key.
</p>
<pre>
var fibonacci = _.memoize(function(n) {
return n < 2 ? n : fibonacci(n - 1) + fibonacci(n - 2);
});
</pre>
<p id="delay">
<b class="header">delay</b><code>_.delay(function, wait, [*arguments])</code>
<br />
Much like <b>setTimeout</b>, invokes <b>function</b> after <b>wait</b>
milliseconds. If you pass the optional <b>arguments</b>, they will be
forwarded on to the <b>function</b> when it is invoked.
</p>
<pre>
var log = _.bind(console.log, console);
_.delay(log, 1000, 'logged later');
=> 'logged later' // Appears after one second.
</pre>
<p id="defer">
<b class="header">defer</b><code>_.defer(function, [*arguments])</code>
<br />
Defers invoking the <b>function</b> until the current call stack has cleared,
similar to using <b>setTimeout</b> with a delay of 0. Useful for performing
expensive computations or HTML rendering in chunks without blocking the UI thread
from updating. If you pass the optional <b>arguments</b>, they will be
forwarded on to the <b>function</b> when it is invoked.
</p>
<pre>
_.defer(function(){ alert('deferred'); });
// Returns from the function before the alert runs.
</pre>
<p id="throttle">
<b class="header">throttle</b><code>_.throttle(function, wait)</code>
<br />
Creates and returns a new, throttled version of the passed function,
that, when invoked repeatedly, will only actually call the original function
at most once per every <b>wait</b>
milliseconds. Useful for rate-limiting events that occur faster than you
can keep up with.
</p>
<pre>
var throttled = _.throttle(updatePosition, 100);
$(window).scroll(throttled);
</pre>
<p id="debounce">
<b class="header">debounce</b><code>_.debounce(function, wait, [immediate])</code>
<br />
Creates and returns a new debounced version of the passed function that
will postpone its execution until after
<b>wait</b> milliseconds have elapsed since the last time it
was invoked. Useful for implementing behavior that should only happen
<i>after</i> the input has stopped arriving. For example: rendering a
preview of a Markdown comment, recalculating a layout after the window
has stopped being resized, and so on.
</p>
<p>
Pass <tt>true</tt> for the <b>immediate</b> parameter to cause
<b>debounce</b> to trigger the function on the leading instead of the
trailing edge of the <b>wait</b> interval. Useful in circumstances like
preventing accidental double-clicks on a "submit" button from firing a
second time.
</p>
<pre>
var lazyLayout = _.debounce(calculateLayout, 300);
$(window).resize(lazyLayout);
</pre>
<p id="once">
<b class="header">once</b><code>_.once(function)</code>
<br />
Creates a version of the function that can only be called one time.
Repeated calls to the modified function will have no effect, returning
the value from the original call. Useful for initialization functions,
instead of having to set a boolean flag and then check it later.
</p>
<pre>
var initialize = _.once(createApplication);
initialize();
initialize();
// Application is only created once.
</pre>
<p id="after">
<b class="header">after</b><code>_.after(count, function)</code>
<br />
Creates a version of the function that will only be run after first
being called <b>count</b> times. Useful for grouping asynchronous responses,
where you want to be sure that all the async calls have finished, before
proceeding.
</p>
<pre>
var renderNotes = _.after(notes.length, render);
_.each(notes, function(note) {
note.asyncSave({success: renderNotes});
});
// renderNotes is run once, after all notes have saved.
</pre>
<p id="wrap">
<b class="header">wrap</b><code>_.wrap(function, wrapper)</code>
<br />
Wraps the first <b>function</b> inside of the <b>wrapper</b> function,
passing it as the first argument. This allows the <b>wrapper</b> to
execute code before and after the <b>function</b> runs, adjust the arguments,
and execute it conditionally.