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  68. </head>
    69. 

  69. <body>
    70. 

  70. 

  71.   <div class="container">
    72. 

  72. 

  73.     <h1>Underscore.js</h1>
    74. 

  74. 

  75.     <p>
    76. 

  76.       <a href="http://github.com/documentcloud/underscore/">Underscore</a> is a
    77. 

  77.       utility-belt library for JavaScript that provides a lot of the
    78. 

  78.       functional programming support that you would expect in
    79. 

  79.       <a href="http://prototypejs.org/api">Prototype.js</a>
    80. 

  80.       (or <a href="http://www.ruby-doc.org/core/classes/Enumerable.html">Ruby</a>),
    81. 

  81.       but without extending any of the built-in JavaScript objects. It's the
    82. 

  82.       tie to go along with <a href="http://docs.jquery.com">jQuery</a>'s tux.
    83. 

  83.     </p>
    84. 

  84. 

  85.     <p>
    86. 

  86.       Underscore provides 60-odd functions that support both the usual
    87. 

  87.       functional suspects: <b>map</b>, <b>select</b>, <b>invoke</b> &mdash;
    88. 

  88.       as well as more specialized helpers: function binding, javascript
    89. 

  89.       templating, deep equality testing, and so on. It delegates to built-in
    90. 

  90.       functions, if present, so modern browsers will use the
    91. 

  91.       native implementations of <b>forEach</b>, <b>map</b>, <b>reduce</b>,
    92. 

  92.       <b>filter</b>, <b>every</b>, <b>some</b> and <b>indexOf</b>.
    93. 

  93.     </p>
    94. 

  94. 

  95.     <p>
    96. 

  96.       A complete <a href="test/test.html">Test &amp; Benchmark Suite</a>
    97. 

  97.       is included for your perusal.
    98. 

  98.     </p>
    99. 

  99.     
    100. 

  100.     <p>
    101. 

  101.       You may also read through the <a href="docs/underscore.html">annotated source code</a>.
    102. 

  102.     </p>
    103. 

  103. 

  104.     <p>
    105. 

  105.       The project is
    106. 

  106.       <a href="http://github.com/documentcloud/underscore/">hosted on GitHub</a>.
    107. 

  107.       You can report bugs and discuss features on the
    108. 

  108.       <a href="http://github.com/documentcloud/underscore/issues">issues page</a>,
    109. 

  109.       on Freenode in the <tt>#documentcloud</tt> channel,
    110. 

  110.       or send tweets to <a href="http://twitter.com/documentcloud">@documentcloud</a>.
    111. 

  111.     </p>
    112. 

  112. 

  113.     <p>
    114. 

  114.       <i>Underscore is an open-source component of <a href="http://documentcloud.org/">DocumentCloud</a>.</i>
    115. 

  115.     </p>
    116. 

  116. 

  117.     <h2>Downloads <i style="padding-left: 12px; font-size:12px;">(Right-click, and use "Save As")</i></h2>
    118. 

  118. 

  119.     <table>
    120. 

  120.       <tr>
    121. 

  121.         <td><a href="underscore.js">Development Version (1.1.7)</a></td>
    122. 

  122.         <td><i>28kb, Uncompressed with Comments</i></td>
    123. 

  123.       </tr>
    124. 

  124.       <tr>
    125. 

  125.         <td><a href="underscore-min.js">Production Version (1.1.7)</a></td>
    126. 

  126.         <td><i>3kb, Minified and Gzipped</i></td>
    127. 

  127.       </tr>
    128. 

  128.     </table>
    129. 

  129. 

  130.     <h2>Table of Contents</h2>
    131. 

  131.     
    132. 

  132.     <a href="#styles">Object-Oriented and Functional Styles</a>
    133. 

  133. 

  134.     <p>
    135. 

  135.       <b>Collections</b>
    136. 

  136.       <br />
    137. 

  137.       <span class="methods"><a href="#each">each</a>, <a href="#map">map</a>,
    138. 

  138.       <a href="#reduce">reduce</a>, <a href="#reduceRight">reduceRight</a>,
    139. 

  139.       <a href="#detect">detect</a>, <a href="#select">select</a>,
    140. 

  140.       <a href="#reject">reject</a>, <a href="#all">all</a>,
    141. 

  141.       <a href="#any">any</a>, <a href="#include">include</a>,
    142. 

  142.       <a href="#invoke">invoke</a>, <a href="#pluck">pluck</a>,
    143. 

  143.       <a href="#max">max</a>, <a href="#min">min</a>,
    144. 

  144.       <a href="#sortBy">sortBy</a>, <a href="#groupBy">groupBy</a>, <a href="#sortedIndex">sortedIndex</a>,
    145. 

  145.       <a href="#toArray">toArray</a>, <a href="#size">size</a></span>
    146. 

  146.     </p>
    147. 

  147. 

  148.     <p>
    149. 

  149.       <b>Arrays</b>
    150. 

  150.       <br />
    151. 

  151.       <span class="methods"><a href="#first">first</a>, <a href="#rest">rest</a>, <a href="#last">last</a>,
    152. 

  152.       <a href="#compact">compact</a>, <a href="#flatten">flatten</a>, <a href="#without">without</a>, 
    153. 

  153.       <a href="#union">union</a>, <a href="#intersection">intersection</a>, <a href="#difference">difference</a>, 
    154. 

  154.       <a href="#uniq">uniq</a>, <a href="#zip">zip</a>, <a href="#indexOf">indexOf</a>,
    155. 

  155.       <a href="#lastIndexOf">lastIndexOf</a>, <a href="#range">range</a></span>
    156. 

  156.     </p>
    157. 

  157. 

  158.     <p>
    159. 

  159.       <b>Functions</b>
    160. 

  160.       <br />
    161. 

  161.       <span class="methods"><a href="#bind">bind</a>, <a href="#bindAll">bindAll</a>, 
    162. 

  162.       <a href="#memoize">memoize</a>, <a href="#delay">delay</a>, <a href="#defer">defer</a>, 
    163. 

  163.       <a href="#throttle">throttle</a>, <a href="#debounce">debounce</a>, 
    164. 

  164.       <a href="#once">once</a>, <a href="#after">after</a>, <a href="#wrap">wrap</a>, <a href="#compose">compose</a></span>
    165. 

  165.     </p>
    166. 

  166. 

  167.     <p>
    168. 

  168.       <b>Objects</b>
    169. 

  169.       <br />
    170. 

  170.       <span class="methods"><a href="#keys">keys</a>, <a href="#values">values</a>,
    171. 

  171.       <a href="#functions">functions</a>, <a href="#extend">extend</a>, <a href="#defaults">defaults</a>, <a href="#clone">clone</a>, <a href="#tap">tap</a>,
    172. 

  172.       <a href="#isEqual">isEqual</a>, <a href="#isEmpty">isEmpty</a>, <a href="#isElement">isElement</a>,
    173. 

  173.       <a href="#isArray">isArray</a>, <a href="#isArguments">isArguments</a>, <a href="#isFunction">isFunction</a>, <a href="#isString">isString</a>,
    174. 

  174.       <a href="#isNumber">isNumber</a>, <a href="#isBoolean">isBoolean</a>, <a href="#isDate">isDate</a>, <a href="#isRegExp">isRegExp</a>
    175. 

  175.       <a href="#isNaN">isNaN</a>, <a href="#isNull">isNull</a>,
    176. 

  176.       <a href="#isUndefined">isUndefined</a>
    177. 

  177.       </span>
    178. 

  178.     </p>
    179. 

  179. 

  180.     <p>
    181. 

  181.       <b>Utility</b>
    182. 

  182.       <br />
    183. 

  183.       <span class="methods"><a href="#noConflict">noConflict</a>,
    184. 

  184.       <a href="#identity">identity</a>, <a href="#times">times</a>, 
    185. 

  185.       <a href="#mixin">mixin</a>, <a href="#uniqueId">uniqueId</a>, 
    186. 

  186.       <a href="#template">template</a></span>
    187. 

  187.     </p>
    188. 

  188. 

  189.     <p>
    190. 

  190.       <b>Chaining</b>
    191. 

  191.       <br />
    192. 

  192.       <span class="methods"><a href="#chain">chain</a>, <a href="#value">value</a>
    193. 

  193.     </p>
    194. 

  194. 

  195.     <div id="documentation">
    196. 

  196.       
    197. 

  197.       <h2 id="styles">Object-Oriented and Functional Styles</h2>
    198. 

  198. 

  199.       <p>
    200. 

  200.         You can use Underscore in either an object-oriented or a functional style,
    201. 

  201.         depending on your preference. The following two lines of code are
    202. 

  202.         identical ways to double a list of numbers.
    203. 

  203.       </p>
    204. 

  204. 

  205.     <pre>
    206. 

  206. _.map([1, 2, 3], function(n){ return n * 2; });
    207. 

  207. _([1, 2, 3]).map(function(n){ return n * 2; });</pre>
    208. 

  208. 

  209.       <p>
    210. 

  210.         Using the object-oriented style allows you to chain together methods. Calling
    211. 

  211.         <tt>chain</tt> on a wrapped object will cause all future method calls to
    212. 

  212.         return wrapped objects as well. When you've finished the computation,
    213. 

  213.         use <tt>value</tt> to retrieve the final value. Here's an example of chaining
    214. 

  214.         together a <b>map/flatten/reduce</b>, in order to get the word count of
    215. 

  215.         every word in a song.
    216. 

  216.       </p>
    217. 

  217. 

  218. <pre>
    219. 

  219. var lyrics = [
    220. 

  220.   {line : 1, words : "I'm a lumberjack and I'm okay"},
    221. 

  221.   {line : 2, words : "I sleep all night and I work all day"},
    222. 

  222.   {line : 3, words : "He's a lumberjack and he's okay"},
    223. 

  223.   {line : 4, words : "He sleeps all night and he works all day"}
    224. 

  224. ];
    225. 

  225. 

  226. _(lyrics).chain()
    227. 

  227.   .map(function(line) { return line.words.split(' '); })
    228. 

  228.   .flatten()
    229. 

  229.   .reduce(function(counts, word) {
    230. 

  230.     counts[word] = (counts[word] || 0) + 1;
    231. 

  231.     return counts;
    232. 

  232. }, {}).value();
    233. 

  233. 

  234. =&gt; {lumberjack : 2, all : 4, night : 2 ... }</pre>
    235. 

  235. 

  236.       <p>
    237. 

  237.         In addition, the
    238. 

  238.         <a href="https://developer.mozilla.org/en/JavaScript/Reference/Global_Objects/Array/prototype">Array prototype's methods</a>
    239. 

  239.         are proxied through the chained Underscore object, so you can slip a
    240. 

  240.         <tt>reverse</tt> or a <tt>push</tt> into your chain, and continue to
    241. 

  241.         modify the array.
    242. 

  242.       </p>
    243. 

  243. 

  244.       <h2>Collection Functions (Arrays or Objects)</h2>
    245. 

  245. 

  246.       <p id="each">
    247. 

  247.         <b class="header">each</b><code>_.each(list, iterator, [context])</code>
    248. 

  248.         <span class="alias">Alias: <b>forEach</b></span>
    249. 

  249.         <br />
    250. 

  250.         Iterates over a <b>list</b> of elements, yielding each in turn to an <b>iterator</b>
    251. 

  251.         function. The <b>iterator</b> is bound to the <b>context</b> object, if one is
    252. 

  252.         passed. Each invocation of <b>iterator</b> is called with three arguments:
    253. 

  253.         <tt>(element, index, list)</tt>. If <b>list</b> is a JavaScript object, <b>iterator</b>'s
    254. 

  254.         arguments will be <tt>(value, key, list)</tt>. Delegates to the native
    255. 

  255.         <b>forEach</b> function if it exists.
    256. 

  256.       </p>
    257. 

  257.       <pre>
    258. 

  258. _.each([1, 2, 3], function(num){ alert(num); });
    259. 

  259. =&gt; alerts each number in turn...
    260. 

  260. _.each({one : 1, two : 2, three : 3}, function(num, key){ alert(num); });
    261. 

  261. =&gt; alerts each number in turn...</pre>
    262. 

  262. 

  263.       <p id="map">
    264. 

  264.         <b class="header">map</b><code>_.map(list, iterator, [context])</code>
    265. 

  265.         <br />
    266. 

  266.         Produces a new array of values by mapping each value in <b>list</b>
    267. 

  267.         through a transformation function (<b>iterator</b>). If the native <b>map</b> method
    268. 

  268.         exists, it will be used instead. If <b>list</b> is a JavaScript object,
    269. 

  269.         <b>iterator</b>'s arguments will be <tt>(value, key, list)</tt>.
    270. 

  270.       </p>
    271. 

  271.       <pre>
    272. 

  272. _.map([1, 2, 3], function(num){ return num * 3; });
    273. 

  273. =&gt; [3, 6, 9]
    274. 

  274. _.map({one : 1, two : 2, three : 3}, function(num, key){ return num * 3; });
    275. 

  275. =&gt; [3, 6, 9]</pre>
    276. 

  276. 

  277.       <p id="reduce">
    278. 

  278.         <b class="header">reduce</b><code>_.reduce(list, iterator, memo, [context])</code>
    279. 

  279.         <span class="alias">Aliases: <b>inject, foldl</b></span>
    280. 

  280.         <br />
    281. 

  281.         Also known as <b>inject</b> and <b>foldl</b>, <b>reduce</b> boils down a
    282. 

  282.         <b>list</b> of values into a single value. <b>Memo</b> is the initial state
    283. 

  283.         of the reduction, and each successive step of it should be returned by
    284. 

  284.         <b>iterator</b>.
    285. 

  285.       </p>
    286. 

  286.       <pre>
    287. 

  287. var sum = _.reduce([1, 2, 3], function(memo, num){ return memo + num; }, 0);
    288. 

  288. =&gt; 6
    289. 

  289. </pre>
    290. 

  290. 

  291.       <p id="reduceRight">
    292. 

  292.         <b class="header">reduceRight</b><code>_.reduceRight(list, iterator, memo, [context])</code>
    293. 

  293.         <span class="alias">Alias: <b>foldr</b></span>
    294. 

  294.         <br />
    295. 

  295.         The right-associative version of <b>reduce</b>. Delegates to the
    296. 

  296.         JavaScript 1.8 version of <b>reduceRight</b>, if it exists. <b>Foldr</b>
    297. 

  297.         is not as useful in JavaScript as it would be in a language with lazy
    298. 

  298.         evaluation.
    299. 

  299.       </p>
    300. 

  300.       <pre>
    301. 

  301. var list = [[0, 1], [2, 3], [4, 5]];
    302. 

  302. var flat = _.reduceRight(list, function(a, b) { return a.concat(b); }, []);
    303. 

  303. =&gt; [4, 5, 2, 3, 0, 1]
    304. 

  304. </pre>
    305. 

  305. 

  306.       <p id="detect">
    307. 

  307.         <b class="header">detect</b><code>_.detect(list, iterator, [context])</code>
    308. 

  308.         <br />
    309. 

  309.         Looks through each value in the <b>list</b>, returning the first one that
    310. 

  310.         passes a truth test (<b>iterator</b>). The function returns as
    311. 

  311.         soon as it finds an acceptable element, and doesn't traverse the
    312. 

  312.         entire list.
    313. 

  313.       </p>
    314. 

  314.       <pre>
    315. 

  315. var even = _.detect([1, 2, 3, 4, 5, 6], function(num){ return num % 2 == 0; });
    316. 

  316. =&gt; 2
    317. 

  317. </pre>
    318. 

  318. 

  319.       <p id="select">
    320. 

  320.         <b class="header">select</b><code>_.select(list, iterator, [context])</code>
    321. 

  321.         <span class="alias">Alias: <b>filter</b></span>
    322. 

  322.         <br />
    323. 

  323.         Looks through each value in the <b>list</b>, returning an array of all
    324. 

  324.         the values that pass a truth test (<b>iterator</b>). Delegates to the
    325. 

  325.         native <b>filter</b> method, if it exists.
    326. 

  326.       </p>
    327. 

  327.       <pre>
    328. 

  328. var evens = _.select([1, 2, 3, 4, 5, 6], function(num){ return num % 2 == 0; });
    329. 

  329. =&gt; [2, 4, 6]
    330. 

  330. </pre>
    331. 

  331. 

  332.       <p id="reject">
    333. 

  333.         <b class="header">reject</b><code>_.reject(list, iterator, [context])</code>
    334. 

  334.         <br />
    335. 

  335.         Returns the values in <b>list</b> without the elements that the truth
    336. 

  336.         test (<b>iterator</b>) passes. The opposite of <b>select</b>.
    337. 

  337.       </p>
    338. 

  338.       <pre>
    339. 

  339. var odds = _.reject([1, 2, 3, 4, 5, 6], function(num){ return num % 2 == 0; });
    340. 

  340. =&gt; [1, 3, 5]
    341. 

  341. </pre>
    342. 

  342. 

  343.       <p id="all">
    344. 

  344.         <b class="header">all</b><code>_.all(list, iterator, [context])</code>
    345. 

  345.         <span class="alias">Alias: <b>every</b></span>
    346. 

  346.         <br />
    347. 

  347.         Returns <i>true</i> if all of the values in the <b>list</b> pass the <b>iterator</b>
    348. 

  348.         truth test. Delegates to the native method <b>every</b>, if present.
    349. 

  349.       </p>
    350. 

  350.       <pre>
    351. 

  351. _.all([true, 1, null, 'yes'], _.identity);
    352. 

  352. =&gt; false
    353. 

  353. </pre>
    354. 

  354. 

  355.       <p id="any">
    356. 

  356.         <b class="header">any</b><code>_.any(list, [iterator], [context])</code>
    357. 

  357.         <span class="alias">Alias: <b>some</b></span>
    358. 

  358.         <br />
    359. 

  359.         Returns <i>true</i> if any of the values in the <b>list</b> pass the
    360. 

  360.         <b>iterator</b> truth test. Short-circuits and stops traversing the list
    361. 

  361.         if a true element is found. Delegates to the native method <b>some</b>,
    362. 

  362.         if present.
    363. 

  363.       </p>
    364. 

  364.       <pre>
    365. 

  365. _.any([null, 0, 'yes', false]);
    366. 

  366. =&gt; true
    367. 

  367. </pre>
    368. 

  368. 

  369.       <p id="include">
    370. 

  370.         <b class="header">include</b><code>_.include(list, value)</code>
    371. 

  371.         <span class="alias">Alias: <b>contains</b></span>
    372. 

  372.         <br />
    373. 

  373.         Returns <i>true</i> if the <b>value</b> is present in the <b>list</b>, using
    374. 

  374.         <i>===</i> to test equality. Uses <b>indexOf</b> internally, if <b>list</b>
    375. 

  375.         is an Array.
    376. 

  376.       </p>
    377. 

  377.       <pre>
    378. 

  378. _.include([1, 2, 3], 3);
    379. 

  379. =&gt; true
    380. 

  380. </pre>
    381. 

  381. 

  382.       <p id="invoke">
    383. 

  383.         <b class="header">invoke</b><code>_.invoke(list, methodName, [*arguments])</code>
    384. 

  384.         <br />
    385. 

  385.         Calls the method named by <b>methodName</b> on each value in the <b>list</b>.
    386. 

  386.         Any extra arguments passed to <b>invoke</b> will be forwarded on to the
    387. 

  387.         method invocation.
    388. 

  388.       </p>
    389. 

  389.       <pre>
    390. 

  390. _.invoke([[5, 1, 7], [3, 2, 1]], 'sort');
    391. 

  391. =&gt; [[1, 5, 7], [1, 2, 3]]
    392. 

  392. </pre>
    393. 

  393. 

  394.       <p id="pluck">
    395. 

  395.         <b class="header">pluck</b><code>_.pluck(list, propertyName)</code>
    396. 

  396.         <br />
    397. 

  397.         A convenient version of what is perhaps the most common use-case for
    398. 

  398.         <b>map</b>: extracting a list of property values.
    399. 

  399.       </p>
    400. 

  400.       <pre>
    401. 

  401. var stooges = [{name : 'moe', age : 40}, {name : 'larry', age : 50}, {name : 'curly', age : 60}];
    402. 

  402. _.pluck(stooges, 'name');
    403. 

  403. =&gt; ["moe", "larry", "curly"]
    404. 

  404. </pre>
    405. 

  405. 

  406.       <p id="max">
    407. 

  407.         <b class="header">max</b><code>_.max(list, [iterator], [context])</code>
    408. 

  408.         <br />
    409. 

  409.         Returns the maximum value in <b>list</b>. If <b>iterator</b> is passed,
    410. 

  410.         it will be used on each value to generate the criterion by which the
    411. 

  411.         value is ranked.
    412. 

  412.       </p>
    413. 

  413.       <pre>
    414. 

  414. var stooges = [{name : 'moe', age : 40}, {name : 'larry', age : 50}, {name : 'curly', age : 60}];
    415. 

  415. _.max(stooges, function(stooge){ return stooge.age; });
    416. 

  416. =&gt; {name : 'curly', age : 60};
    417. 

  417. </pre>
    418. 

  418. 

  419.       <p id="min">
    420. 

  420.         <b class="header">min</b><code>_.min(list, [iterator], [context])</code>
    421. 

  421.         <br />
    422. 

  422.         Returns the minimum value in <b>list</b>. If <b>iterator</b> is passed,
    423. 

  423.         it will be used on each value to generate the criterion by which the
    424. 

  424.         value is ranked.
    425. 

  425.       </p>
    426. 

  426.       <pre>
    427. 

  427. var numbers = [10, 5, 100, 2, 1000];
    428. 

  428. _.min(numbers);
    429. 

  429. =&gt; 2
    430. 

  430. </pre>
    431. 

  431. 

  432.       <p id="sortBy">
    433. 

  433.         <b class="header">sortBy</b><code>_.sortBy(list, iterator, [context])</code>
    434. 

  434.         <br />
    435. 

  435.         Returns a sorted copy of <b>list</b>, ranked by the results of running 
    436. 

  436.         each value through <b>iterator</b>.
    437. 

  437.       </p>
    438. 

  438.       <pre>
    439. 

  439. _.sortBy([1, 2, 3, 4, 5, 6], function(num){ return Math.sin(num); });
    440. 

  440. =&gt; [5, 4, 6, 3, 1, 2]
    441. 

  441. </pre>
    442. 

  442. 

  443.       <p id="groupBy">
    444. 

  444.         <b class="header">groupBy</b><code>_.groupBy(list, iterator)</code>
    445. 

  445.         <br />
    446. 

  446.         Splits a collection into sets, grouped by the result of running each
    447. 

  447.         value through <b>iterator</b>.
    448. 

  448.       </p>
    449. 

  449.       <pre>
    450. 

  450. _.groupBy([1.3, 2.1, 2.4], function(num){ return Math.floor(num); });
    451. 

  451. =&gt; {1: [1.3], 2: [2.1, 2.4]}
    452. 

  452. </pre>
    453. 

  453. 

  454.       <p id="sortedIndex">
    455. 

  455.         <b class="header">sortedIndex</b><code>_.sortedIndex(list, value, [iterator])</code>
    456. 

  456.         <br />
    457. 

  457.         Uses a binary search to determine the index at which the <b>value</b>
    458. 

  458.         <i>should</i> be inserted into the <b>list</b> in order to maintain the <b>list</b>'s
    459. 

  459.         sorted order. If an <b>iterator</b> is passed, it will be used to compute
    460. 

  460.         the sort ranking of each value.
    461. 

  461.       </p>
    462. 

  462.       <pre>
    463. 

  463. _.sortedIndex([10, 20, 30, 40, 50], 35);
    464. 

  464. =&gt; 3
    465. 

  465. </pre>
    466. 

  466. 

  467.       <p id="toArray">
    468. 

  468.         <b class="header">toArray</b><code>_.toArray(list)</code>
    469. 

  469.         <br />
    470. 

  470.         Converts the <b>list</b> (anything that can be iterated over), into a
    471. 

  471.         real Array. Useful for transmuting the <b>arguments</b> object.
    472. 

  472.       </p>
    473. 

  473.       <pre>
    474. 

  474. (function(){ return _.toArray(arguments).slice(0); })(1, 2, 3);
    475. 

  475. =&gt; [1, 2, 3]
    476. 

  476. </pre>
    477. 

  477. 

  478.       <p id="size">
    479. 

  479.         <b class="header">size</b><code>_.size(list)</code>
    480. 

  480.         <br />
    481. 

  481.         Return the number of values in the <b>list</b>.
    482. 

  482.       </p>
    483. 

  483.       <pre>
    484. 

  484. _.size({one : 1, two : 2, three : 3});
    485. 

  485. =&gt; 3
    486. 

  486. </pre>
    487. 

  487. 

  488.       <h2>Array Functions</h2>
    489. 

  489. 

  490.       <p>
    491. 

  491.         <i>Note: All array functions will also work on the <b>arguments</b> object.</i>
    492. 

  492.       </p>
    493. 

  493. 

  494.       <p id="first">
    495. 

  495.         <b class="header">first</b><code>_.first(array, [n])</code>
    496. 

  496.         <span class="alias">Alias: <b>head</b></span>
    497. 

  497.         <br />
    498. 

  498.         Returns the first element of an <b>array</b>. Passing <b>n</b> will
    499. 

  499.         return the first <b>n</b> elements of the array.
    500. 

  500.       </p>
    501. 

  501.       <pre>
    502. 

  502. _.first([5, 4, 3, 2, 1]);
    503. 

  503. =&gt; 5
    504. 

  504. </pre>
    505. 

  505. 

  506.       <p id="rest">
    507. 

  507.         <b class="header">rest</b><code>_.rest(array, [index])</code>
    508. 

  508.         <span class="alias">Alias: <b>tail</b></span>
    509. 

  509.         <br />
    510. 

  510.         Returns the <b>rest</b> of the elements in an array. Pass an <b>index</b>
    511. 

  511.         to return the values of the array from that index onward.
    512. 

  512.       </p>
    513. 

  513.       <pre>
    514. 

  514. _.rest([5, 4, 3, 2, 1]);
    515. 

  515. =&gt; [4, 3, 2, 1]
    516. 

  516. </pre>
    517. 

  517. 

  518.       <p id="last">
    519. 

  519.         <b class="header">last</b><code>_.last(array)</code>
    520. 

  520.         <br />
    521. 

  521.         Returns the last element of an <b>array</b>.
    522. 

  522.       </p>
    523. 

  523.       <pre>
    524. 

  524. _.last([5, 4, 3, 2, 1]);
    525. 

  525. =&gt; 1
    526. 

  526. </pre>
    527. 

  527. 

  528.       <p id="compact">
    529. 

  529.         <b class="header">compact</b><code>_.compact(array)</code>
    530. 

  530.         <br />
    531. 

  531.         Returns a copy of the <b>array</b> with all falsy values removed.
    532. 

  532.         In JavaScript, <i>false</i>, <i>null</i>, <i>0</i>, <i>""</i>,
    533. 

  533.         <i>undefined</i> and <i>NaN</i> are all falsy.
    534. 

  534.       </p>
    535. 

  535.       <pre>
    536. 

  536. _.compact([0, 1, false, 2, '', 3]);
    537. 

  537. =&gt; [1, 2, 3]
    538. 

  538. </pre>
    539. 

  539. 

  540.       <p id="flatten">
    541. 

  541.         <b class="header">flatten</b><code>_.flatten(array)</code>
    542. 

  542.         <br />
    543. 

  543.         Flattens a nested <b>array</b> (the nesting can be to any depth).
    544. 

  544.       </p>
    545. 

  545.       <pre>
    546. 

  546. _.flatten([1, [2], [3, [[[4]]]]]);
    547. 

  547. =&gt; [1, 2, 3, 4];
    548. 

  548. </pre>
    549. 

  549. 

  550.       <p id="without">
    551. 

  551.         <b class="header">without</b><code>_.without(array, [*values])</code>
    552. 

  552.         <br />
    553. 

  553.         Returns a copy of the <b>array</b> with all instances of the <b>values</b>
    554. 

  554.         removed. <i>===</i> is used for the equality test.
    555. 

  555.       </p>
    556. 

  556.       <pre>
    557. 

  557. _.without([1, 2, 1, 0, 3, 1, 4], 0, 1);
    558. 

  558. =&gt; [2, 3, 4]
    559. 

  559. </pre>
    560. 

  560. 

  561.       <p id="union">
    562. 

  562.         <b class="header">union</b><code>_.union(*arrays)</code>
    563. 

  563.         <br />
    564. 

  564.         Computes the union of the passed-in <b>arrays</b>: the list of unique items,
    565. 

  565.         in order, that are present in one or more of the <b>arrays</b>.
    566. 

  566.       </p>
    567. 

  567.       <pre>
    568. 

  568. _.union([1, 2, 3], [101, 2, 1, 10], [2, 1]);
    569. 

  569. =&gt; [1, 2, 3, 101, 10]
    570. 

  570. </pre>
    571. 

  571. 

  572.       <p id="intersection">
    573. 

  573.         <b class="header">intersection</b><code>_.intersection(*arrays)</code>
    574. 

  574.         <br />
    575. 

  575.         Computes the list of values that are the intersection of all the <b>arrays</b>.
    576. 

  576.         Each value in the result is present in each of the <b>arrays</b>.
    577. 

  577.       </p>
    578. 

  578.       <pre>
    579. 

  579. _.intersection([1, 2, 3], [101, 2, 1, 10], [2, 1]);
    580. 

  580. =&gt; [1, 2]
    581. 

  581. </pre>
    582. 

  582. 

  583.       <p id="difference">
    584. 

  584.         <b class="header">difference</b><code>_.difference(array, other)</code>
    585. 

  585.         <br />
    586. 

  586.         Similar to <b>without</b>, but returns the values from <b>array</b> that
    587. 

  587.         are not present in <b>other</b>.
    588. 

  588.       </p>
    589. 

  589.       <pre>
    590. 

  590. _.difference([1, 2, 3, 4, 5], [5, 2, 10]);
    591. 

  591. =&gt; [1, 3, 4]
    592. 

  592. </pre>
    593. 

  593. 

  594.       <p id="uniq">
    595. 

  595.         <b class="header">uniq</b><code>_.uniq(array, [isSorted], [iterator])</code>
    596. 

  596.         <span class="alias">Alias: <b>unique</b></span>
    597. 

  597.         <br />
    598. 

  598.         Produces a duplicate-free version of the <b>array</b>, using <i>===</i> to test
    599. 

  599.         object equality. If you know in advance that the <b>array</b> is sorted,
    600. 

  600.         passing <i>true</i> for <b>isSorted</b> will run a much faster algorithm.
    601. 

  601.         If you want to compute unique items based on a transformation, pass an
    602. 

  602.         <b>iterator</b> function.
    603. 

  603.       </p>
    604. 

  604.       <pre>
    605. 

  605. _.uniq([1, 2, 1, 3, 1, 4]);
    606. 

  606. =&gt; [1, 2, 3, 4]
    607. 

  607. </pre>
    608. 

  608. 

  609.       <p id="zip">
    610. 

  610.         <b class="header">zip</b><code>_.zip(*arrays)</code>
    611. 

  611.         <br />
    612. 

  612.         Merges together the values of each of the <b>arrays</b> with the
    613. 

  613.         values at the corresponding position. Useful when you have separate
    614. 

  614.         data sources that are coordinated through matching array indexes.
    615. 

  615.         If you're working with a matrix of nested arrays, <b>zip.apply</b>
    616. 

  616.         can transpose the matrix in a similar fashion.
    617. 

  617.       </p>
    618. 

  618.       <pre>
    619. 

  619. _.zip(['moe', 'larry', 'curly'], [30, 40, 50], [true, false, false]);
    620. 

  620. =&gt; [["moe", 30, true], ["larry", 40, false], ["curly", 50, false]]
    621. 

  621. </pre>
    622. 

  622. 

  623.       <p id="indexOf">
    624. 

  624.         <b class="header">indexOf</b><code>_.indexOf(array, value, [isSorted])</code>
    625. 

  625.         <br />
    626. 

  626.         Returns the index at which <b>value</b> can be found in the <b>array</b>,
    627. 

  627.         or <i>-1</i> if value is not present in the <b>array</b>. Uses the native
    628. 

  628.         <b>indexOf</b> function unless it's missing. If you're working with a 
    629. 

  629.         large array, and you know that the array is already sorted, pass <tt>true</tt>
    630. 

  630.         for <b>isSorted</b> to use a faster binary search.
    631. 

  631.       </p>
    632. 

  632.       <pre>
    633. 

  633. _.indexOf([1, 2, 3], 2);
    634. 

  634. =&gt; 1
    635. 

  635. </pre>
    636. 

  636. 

  637.       <p id="lastIndexOf">
    638. 

  638.         <b class="header">lastIndexOf</b><code>_.lastIndexOf(array, value)</code>
    639. 

  639.         <br />
    640. 

  640.         Returns the index of the last occurrence of <b>value</b> in the <b>array</b>,
    641. 

  641.         or <i>-1</i> if value is not present. Uses the native <b>lastIndexOf</b>
    642. 

  642.         function if possible.
    643. 

  643.       </p>
    644. 

  644.       <pre>
    645. 

  645. _.lastIndexOf([1, 2, 3, 1, 2, 3], 2);
    646. 

  646. =&gt; 4
    647. 

  647. </pre>
    648. 

  648. 

  649.       <p id="range">
    650. 

  650.         <b class="header">range</b><code>_.range([start], stop, [step])</code>
    651. 

  651.         <br />
    652. 

  652.         A function to create flexibly-numbered lists of integers, handy for
    653. 

  653.         <tt>each</tt> and <tt>map</tt> loops. <b>start</b>, if omitted, defaults
    654. 

  654.         to <i>0</i>; <b>step</b> defaults to <i>1</i>. Returns a list of integers
    655. 

  655.         from <b>start</b> to <b>stop</b>, incremented (or decremented) by <b>step</b>,
    656. 

  656.         exclusive.
    657. 

  657.       </p>
    658. 

  658.       <pre>
    659. 

  659. _.range(10);
    660. 

  660. =&gt; [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
    661. 

  661. _.range(1, 11);
    662. 

  662. =&gt; [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
    663. 

  663. _.range(0, 30, 5);
    664. 

  664. =&gt; [0, 5, 10, 15, 20, 25]
    665. 

  665. _.range(0, -10, -1);
    666. 

  666. =&gt; [0, -1, -2, -3, -4, -5, -6, -7, -8, -9]
    667. 

  667. _.range(0);
    668. 

  668. =&gt; []
    669. 

  669. </pre>
    670. 

  670. 

  671.       <h2>Function (uh, ahem) Functions</h2>
    672. 

  672. 

  673.       <p id="bind">
    674. 

  674.         <b class="header">bind</b><code>_.bind(function, object, [*arguments])</code>
    675. 

  675.         <br />
    676. 

  676.         Bind a <b>function</b> to an <b>object</b>, meaning that whenever
    677. 

  677.         the function is called, the value of <i>this</i> will be the <b>object</b>.
    678. 

  678.         Optionally, bind <b>arguments</b> to the <b>function</b> to pre-fill them,
    679. 

  679.         also known as <b>currying</b>.
    680. 

  680.       </p>
    681. 

  681.       <pre>
    682. 

  682. var func = function(greeting){ return greeting + ': ' + this.name };
    683. 

  683. func = _.bind(func, {name : 'moe'}, 'hi');
    684. 

  684. func();
    685. 

  685. =&gt; 'hi: moe'
    686. 

  686. </pre>
    687. 

  687. 

  688.       <p id="bindAll">
    689. 

  689.         <b class="header">bindAll</b><code>_.bindAll(object, [*methodNames])</code>
    690. 

  690.         <br />
    691. 

  691.         Binds a number of methods on the <b>object</b>, specified by
    692. 

  692.         <b>methodNames</b>, to be run in the context of that object whenever they
    693. 

  693.         are invoked. Very handy for binding functions that are going to be used
    694. 

  694.         as event handlers, which would otherwise be invoked with a fairly useless
    695. 

  695.         <i>this</i>. If no <b>methodNames</b> are provided, all of the object's
    696. 

  696.         function properties will be bound to it.
    697. 

  697.       </p>
    698. 

  698.       <pre>
    699. 

  699. var buttonView = {
    700. 

  700.   label   : 'underscore',
    701. 

  701.   onClick : function(){ alert('clicked: ' + this.label); },
    702. 

  702.   onHover : function(){ console.log('hovering: ' + this.label); }
    703. 

  703. };
    704. 

  704. _.bindAll(buttonView);
    705. 

  705. jQuery('#underscore_button').bind('click', buttonView.onClick);
    706. 

  706. =&gt; When the button is clicked, this.label will have the correct value...
    707. 

  707. </pre>
    708. 

  708. 

  709.       <p id="memoize">
    710. 

  710.         <b class="header">memoize</b><code>_.memoize(function, [hashFunction])</code>
    711. 

  711.         <br />
    712. 

  712.         Memoizes a given <b>function</b> by caching the computed result. Useful
    713. 

  713.         for speeding up slow-running computations. If passed an optional 
    714. 

  714.         <b>hashFunction</b>, it will be used to compute the hash key for storing
    715. 

  715.         the result, based on the arguments to the original function. The default
    716. 

  716.         <b>hashFunction</b> just uses the first argument to the memoized function
    717. 

  717.         as the key.
    718. 

  718.       </p>
    719. 

  719.       <pre>
    720. 

  720. var fibonacci = function(n) {
    721. 

  721.   return n &lt; 2 ? n : fibonacci(n - 1) + fibonacci(n - 2);
    722. 

  722. };
    723. 

  723. var fastFibonacci = _.memoize(fibonacci);
    724. 

  724. </pre>
    725. 

  725. 

  726.       <p id="delay">
    727. 

  727.         <b class="header">delay</b><code>_.delay(function, wait, [*arguments])</code>
    728. 

  728.         <br />
    729. 

  729.         Much like <b>setTimeout</b>, invokes <b>function</b> after <b>wait</b>
    730. 

  730.         milliseconds. If you pass the optional <b>arguments</b>, they will be
    731. 

  731.         forwarded on to the <b>function</b> when it is invoked.
    732. 

  732.       </p>
    733. 

  733.       <pre>
    734. 

  734. var log = _.bind(console.log, console);
    735. 

  735. _.delay(log, 1000, 'logged later');
    736. 

  736. =&gt; 'logged later' // Appears after one second.
    737. 

  737. </pre>
    738. 

  738. 

  739.       <p id="defer">
    740. 

  740.         <b class="header">defer</b><code>_.defer(function)</code>
    741. 

  741.         <br />
    742. 

  742.         Defers invoking the <b>function</b> until the current call stack has cleared,
    743. 

  743.         similar to using <b>setTimeout</b> with a delay of 0. Useful for performing
    744. 

  744.         expensive computations or HTML rendering in chunks without blocking the UI thread
    745. 

  745.         from updating.
    746. 

  746.       </p>
    747. 

  747.       <pre>
    748. 

  748. _.defer(function(){ alert('deferred'); });
    749. 

  749. // Returns from the function before the alert runs.
    750. 

  750. </pre>
    751. 

  751. 

  752.       <p id="throttle">
    753. 

  753.         <b class="header">throttle</b><code>_.throttle(function, wait)</code>
    754. 

  754.         <br />
    755. 

  755.         Returns a throttled version of the function, that, when invoked repeatedly, 
    756. 

  756.         will only actually call the wrapped function at most once per every <b>wait</b>
    757. 

  757.         milliseconds. Useful for rate-limiting events that occur faster than you
    758. 

  758.         can keep up with.
    759. 

  759.       </p>
    760. 

  760.       <pre>
    761. 

  761. var throttled = _.throttle(updatePosition, 100);
    762. 

  762. $(window).scroll(throttled);
    763. 

  763. </pre>
    764. 

  764. 

  765.       <p id="debounce">
    766. 

  766.         <b class="header">debounce</b><code>_.debounce(function, wait)</code>
    767. 

  767.         <br />
    768. 

  768.         Repeated calls to a debounced function will postpone it's execution
    769. 

  769.         until after <b>wait</b> milliseconds have elapsed. Useful for implementing
    770. 

  770.         behavior that should only happen <i>after</i> the input has stopped arriving.
    771. 

  771.         For example: rendering a preview of a Markdown comment, recalculating a
    772. 

  772.         layout after the window has stopped being resized...
    773. 

  773.       </p>
    774. 

  774.       <pre>
    775. 

  775. var lazyLayout = _.debounce(calculateLayout, 300);
    776. 

  776. $(window).resize(lazyLayout);
    777. 

  777. </pre>
    778. 

  778. 

  779.       <p id="once">
    780. 

  780.         <b class="header">once</b><code>_.once(function)</code>
    781. 

  781.         <br />
    782. 

  782.         Creates a version of the function that can only be called one time. 
    783. 

  783.         Repeated calls to the modified function will have no effect, returning
    784. 

  784.         the value from the original call. Useful for initialization functions,
    785. 

  785.         instead of having to set a boolean flag and then check it later.
    786. 

  786.       </p>
    787. 

  787.       <pre>
    788. 

  788. var initialize = _.once(createApplication);
    789. 

  789. initialize();
    790. 

  790. initialize();
    791. 

  791. // Application is only created once.
    792. 

  792. </pre>
    793. 

  793. 

  794.       <p id="after">
    795. 

  795.         <b class="header">after</b><code>_.after(count, function)</code>
    796. 

  796.         <br />
    797. 

  797.         Creates a version of the function that will only be run after first 
    798. 

  798.         being called <b>count</b> times. Useful for grouping asynchronous responses,
    799. 

  799.         where you want to be sure that all the async calls have finished, before
    800. 

  800.         proceeding.
    801. 

  801.       </p>
    802. 

  802.       <pre>
    803. 

  803. var renderNotes = _.after(notes.length, render);
    804. 

  804. _.each(notes, function(note) {
    805. 

  805.   note.asyncSave({success: renderNotes}); 
    806. 

  806. });
    807. 

  807. // renderNotes is run once, after all notes have saved.
    808. 

  808. </pre>
    809. 

  809. 

  810.       <p id="wrap">
    811. 

  811.         <b class="header">wrap</b><code>_.wrap(function, wrapper)</code>
    812. 

  812.         <br />
    813. 

  813.         Wraps the first <b>function</b> inside of the <b>wrapper</b> function,
    814. 

  814.         passing it as the first argument. This allows the <b>wrapper</b> to
    815. 

  815.         execute code before and after the <b>function</b> runs, adjust the arguments,
    816. 

  816.         and execute it conditionally.
    817. 

  817.       </p>
    818. 

  818.       <pre>
    819. 

  819. var hello = function(name) { return "hello: " + name; };
    820. 

  820. hello = _.wrap(hello, function(func) {
    821. 

  821.   return "before, " + func("moe") + ", after";
    822. 

  822. });
    823. 

  823. hello();
    824. 

  824. =&gt; 'before, hello: moe, after'
    825. 

  825. </pre>
    826. 

  826. 

  827.       <p id="compose">
    828. 

  828.         <b class="header">compose</b><code>_.compose(*functions)</code>
    829. 

  829.         <br />
    830. 

  830.         Returns the composition of a list of <b>functions</b>, where each function
    831. 

  831.         consumes the return value of the function that follows. In math terms,
    832. 

  832.         composing the functions <i>f()</i>, <i>g()</i>, and <i>h()</i> produces
    833. 

  833.         <i>f(g(h()))</i>.
    834. 

  834.       </p>
    835. 

  835.       <pre>
    836. 

  836. var greet    = function(name){ return "hi: " + name; };
    837. 

  837. var exclaim  = function(statement){ return statement + "!"; };
    838. 

  838. var welcome = _.compose(exclaim, greet);
    839. 

  839. welcome('moe');
    840. 

  840. =&gt; 'hi: moe!'
    841. 

  841. </pre>
    842. 

  842. 

  843.       <h2>Object Functions</h2>
    844. 

  844. 

  845.       <p id="keys">
    846. 

  846.         <b class="header">keys</b><code>_.keys(object)</code>
    847. 

  847.         <br />
    848. 

  848.         Retrieve all the names of the <b>object</b>'s properties.
    849. 

  849.       </p>
    850. 

  850.       <pre>
    851. 

  851. _.keys({one : 1, two : 2, three : 3});
    852. 

  852. =&gt; ["one", "two", "three"]
    853. 

  853. </pre>
    854. 

  854. 

  855.       <p id="values">
    856. 

  856.         <b class="header">values</b><code>_.values(object)</code>
    857. 

  857.         <br />
    858. 

  858.         Return all of the values of the <b>object</b>'s properties.
    859. 

  859.       </p>
    860. 

  860.       <pre>
    861. 

  861. _.values({one : 1, two : 2, three : 3});
    862. 

  862. =&gt; [1, 2, 3]
    863. 

  863. </pre>
    864. 

  864. 

  865.       <p id="functions">
    866. 

  866.         <b class="header">functions</b><code>_.functions(object)</code>
    867. 

  867.         <span class="alias">Alias: <b>methods</b></span>
    868. 

  868.         <br />
    869. 

  869.         Returns a sorted list of the names of every method in an object &mdash;
    870. 

  870.         that is to say, the name of every function property of the object.
    871. 

  871.       </p>
    872. 

  872.       <pre>
    873. 

  873. _.functions(_);
    874. 

  874. =&gt; ["all", "any", "bind", "bindAll", "clone", "compact", "compose" ...
    875. 

  875. </pre>
    876. 

  876. 

  877.       <p id="extend">
    878. 

  878.         <b class="header">extend</b><code>_.extend(destination, *sources)</code>
    879. 

  879.         <br />
    880. 

  880.         Copy all of the properties in the <b>source</b> objects over to the
    881. 

  881.         <b>destination</b> object. It's in-order, to the last source will override
    882. 

  882.         properties of the same name in previous arguments.
    883. 

  883.       </p>
    884. 

  884.       <pre>
    885. 

  885. _.extend({name : 'moe'}, {age : 50});
    886. 

  886. =&gt; {name : 'moe', age : 50}
    887. 

  887. </pre>
    888. 

  888. 

  889.       <p id="defaults">
    890. 

  890.         <b class="header">defaults</b><code>_.defaults(object, *defaults)</code>
    891. 

  891.         <br />
    892. 

  892.         Fill in missing properties in <b>object</b> with default values from the
    893. 

  893.         <b>defaults</b> objects. As soon as the property is filled, further defaults
    894. 

  894.         will have no effect.
    895. 

  895.       </p>
    896. 

  896.       <pre>
    897. 

  897. var iceCream = {flavor : "chocolate"};
    898. 

  898. _.defaults(iceCream, {flavor : "vanilla", sprinkles : "lots"});
    899. 

  899. =&gt; {flavor : "chocolate", sprinkles : "lots"}
    900. 

  900. </pre>
    901. 

  901. 

  902.       <p id="clone">
    903. 

  903.         <b class="header">clone</b><code>_.clone(object)</code>
    904. 

  904.         <br />
    905. 

  905.         Create a shallow-copied clone of the <b>object</b>. Any nested objects
    906. 

  906.         or arrays will be copied by reference, not duplicated.
    907. 

  907.       </p>
    908. 

  908.       <pre>
    909. 

  909. _.clone({name : 'moe'});
    910. 

  910. =&gt; {name : 'moe'};
    911. 

  911. </pre>
    912. 

  912. 

  913.       <p id="tap">
    914. 

  914.         <b class="header">tap</b><code>_.tap(object, interceptor)</code>
    915. 

  915.         <br />
    916. 

  916.         Invokes <b>interceptor</b> with the <b>object</b>, and then returns <b>object</b>.
    917. 

  917.         The primary purpose of this method is to "tap into" a method chain, in order to perform operations on intermediate results within the chain.
    918. 

  918.       </p>
    919. 

  919.       <pre>
    920. 

  920. _([1,2,3,200]).chain().
    921. 

  921.   select(function(num) { return num % 2 == 0; }).
    922. 

  922.   tap(console.log).
    923. 

  923.   map(function(num) { return num * num }).
    924. 

  924.   value();
    925. 

  925. =&gt; [2, 200]
    926. 

  926. =&gt; [4, 40000]
    927. 

  927. </pre>
    928. 

  928. 

  929.       <p id="isEqual">
    930. 

  930.         <b class="header">isEqual</b><code>_.isEqual(object, other)</code>
    931. 

  931.         <br />
    932. 

  932.         Performs an optimized deep comparison between the two objects, to determine
    933. 

  933.         if they should be considered equal.
    934. 

  934.       </p>
    935. 

  935.       <pre>
    936. 

  936. var moe   = {name : 'moe', luckyNumbers : [13, 27, 34]};
    937. 

  937. var clone = {name : 'moe', luckyNumbers : [13, 27, 34]};
    938. 

  938. moe == clone;
    939. 

  939. =&gt; false
    940. 

  940. _.isEqual(moe, clone);
    941. 

  941. =&gt; true
    942. 

  942. </pre>
    943. 

  943. 

  944.       <p id="isEmpty">
    945. 

  945.         <b class="header">isEmpty</b><code>_.isEmpty(object)</code>
    946. 

  946.         <br />
    947. 

  947.         Returns <i>true</i> if <b>object</b> contains no values.
    948. 

  948.       </p>
    949. 

  949.       <pre>
    950. 

  950. _.isEmpty([1, 2, 3]);
    951. 

  951. =&gt; false
    952. 

  952. _.isEmpty({});
    953. 

  953. =&gt; true
    954. 

  954. </pre>
    955. 

  955. 

  956.       <p id="isElement">
    957. 

  957.         <b class="header">isElement</b><code>_.isElement(object)</code>
    958. 

  958.         <br />
    959. 

  959.         Returns <i>true</i> if <b>object</b> is a DOM element.
    960. 

  960.       </p>
    961. 

  961.       <pre>
    962. 

  962. _.isElement(jQuery('body')[0]);
    963. 

  963. =&gt; true
    964. 

  964. </pre>
    965. 

  965. 

  966.       <p id="isArray">
    967. 

  967.         <b class="header">isArray</b><code>_.isArray(object)</code>
    968. 

  968.         <br />
    969. 

  969.         Returns <i>true</i> if <b>object</b> is an Array.
    970. 

  970.       </p>
    971. 

  971.       <pre>
    972. 

  972. (function(){ return _.isArray(arguments); })();
    973. 

  973. =&gt; false
    974. 

  974. _.isArray([1,2,3]);
    975. 

  975. =&gt; true
    976. 

  976. </pre>
    977. 

  977. 

  978.       <p id="isArguments">
    979. 

  979.         <b class="header">isArguments</b><code>_.isArguments(object)</code>
    980. 

  980.         <br />
    981. 

  981.         Returns <i>true</i> if <b>object</b> is an Arguments object.
    982. 

  982.       </p>
    983. 

  983.       <pre>
    984. 

  984. (function(){ return _.isArguments(arguments); })(1, 2, 3);
    985. 

  985. =&gt; true
    986. 

  986. _.isArguments([1,2,3]);
    987. 

  987. =&gt; false
    988. 

  988. </pre>
    989. 

  989. 

  990.       <p id="isFunction">
    991. 

  991.         <b class="header">isFunction</b><code>_.isFunction(object)</code>
    992. 

  992.         <br />
    993. 

  993.         Returns <i>true</i> if <b>object</b> is a Function.
    994. 

  994.       </p>
    995. 

  995.       <pre>
    996. 

  996. _.isFunction(alert);
    997. 

  997. =&gt; true
    998. 

  998. </pre>
    999. 

  999. 

  1000.       <p id="isString">
    1001. 

  1001.         <b class="header">isString</b><code>_.isString(object)</code>
    1002. 

  1002.         <br />
    1003. 

  1003.         Returns <i>true</i> if <b>object</b> is a String.
    1004. 

  1004.       </p>
    1005. 

  1005.       <pre>
    1006. 

  1006. _.isString("moe");
    1007. 

  1007. =&gt; true
    1008. 

  1008. </pre>
    1009. 

  1009. 

  1010.       <p id="isNumber">
    1011. 

  1011.         <b class="header">isNumber</b><code>_.isNumber(object)</code>
    1012. 

  1012.         <br />
    1013. 

  1013.         Returns <i>true</i> if <b>object</b> is a Number.
    1014. 

  1014.       </p>
    1015. 

  1015.       <pre>
    1016. 

  1016. _.isNumber(8.4 * 5);
    1017. 

  1017. =&gt; true
    1018. 

  1018. </pre>
    1019. 

  1019. 

  1020.       <p id="isBoolean">
    1021. 

  1021.         <b class="header">isBoolean</b><code>_.isBoolean(object)</code>
    1022. 

  1022.         <br />
    1023. 

  1023.         Returns <i>true</i> if <b>object</b> is either <i>true</i> or <i>false</i>.
    1024. 

  1024.       </p>
    1025. 

  1025.       <pre>
    1026. 

  1026. _.isBoolean(null);
    1027. 

  1027. =&gt; false
    1028. 

  1028. </pre>
    1029. 

  1029. 

  1030.       <p id="isDate">
    1031. 

  1031.         <b class="header">isDate</b><code>_.isDate(object)</code>
    1032. 

  1032.         <br />
    1033. 

  1033.         Returns <i>true</i> if <b>object</b> is a Date.
    1034. 

  1034.       </p>
    1035. 

  1035.       <pre>
    1036. 

  1036. _.isDate(new Date());
    1037. 

  1037. =&gt; true
    1038. 

  1038. </pre>
    1039. 

  1039. 

  1040.       <p id="isRegExp">
    1041. 

  1041.         <b class="header">isRegExp</b><code>_.isRegExp(object)</code>
    1042. 

  1042.         <br />
    1043. 

  1043.         Returns <i>true</i> if <b>object</b> is a RegExp.
    1044. 

  1044.       </p>
    1045. 

  1045.       <pre>
    1046. 

  1046. _.isRegExp(/moe/);
    1047. 

  1047. =&gt; true
    1048. 

  1048. </pre>
    1049. 

  1049. 

  1050.       <p id="isNaN">
    1051. 

  1051.         <b class="header">isNaN</b><code>_.isNaN(object)</code>
    1052. 

  1052.         <br />
    1053. 

  1053.         Returns <i>true</i> if <b>object</b> is <i>NaN</i>.<br /> Note: this is not
    1054. 

  1054.         the same as the native <b>isNaN</b> function, which will also return
    1055. 

  1055.         true if the variable is <i>undefined</i>.
    1056. 

  1056.       </p>
    1057. 

  1057.       <pre>
    1058. 

  1058. _.isNaN(NaN);
    1059. 

  1059. =&gt; true
    1060. 

  1060. isNaN(undefined);
    1061. 

  1061. =&gt; true
    1062. 

  1062. _.isNaN(undefined);
    1063. 

  1063. =&gt; false
    1064. 

  1064. </pre>
    1065. 

  1065. 

  1066.       <p id="isNull">
    1067. 

  1067.         <b class="header">isNull</b><code>_.isNull(object)</code>
    1068. 

  1068.         <br />
    1069. 

  1069.         Returns <i>true</i> if the value of <b>object</b> is <i>null</i>.
    1070. 

  1070.       </p>
    1071. 

  1071.       <pre>
    1072. 

  1072. _.isNull(null);
    1073. 

  1073. =&gt; true
    1074. 

  1074. _.isNull(undefined);
    1075. 

  1075. =&gt; false
    1076. 

  1076. </pre>
    1077. 

  1077. 

  1078.       <p id="isUndefined">
    1079. 

  1079.         <b class="header">isUndefined</b><code>_.isUndefined(variable)</code>
    1080. 

  1080.         <br />
    1081. 

  1081.         Returns <i>true</i> if <b>variable</b> is <i>undefined</i>.
    1082. 

  1082.       </p>
    1083. 

  1083.       <pre>
    1084. 

  1084. _.isUndefined(window.missingVariable);
    1085. 

  1085. =&gt; true
    1086. 

  1086. </pre>
    1087. 

  1087. 

  1088.       <h2>Utility Functions</h2>
    1089. 

  1089. 

  1090.       <p id="noConflict">
    1091. 

  1091.         <b class="header">noConflict</b><code>_.noConflict()</code>
    1092. 

  1092.         <br />
    1093. 

  1093.         Give control of the "_" variable back to its previous owner. Returns
    1094. 

  1094.         a reference to the <b>Underscore</b> object.
    1095. 

  1095.       </p>
    1096. 

  1096.       <pre>
    1097. 

  1097. var underscore = _.noConflict();</pre>
    1098. 

  1098. 

  1099.       <p id="identity">
    1100. 

  1100.         <b class="header">identity</b><code>_.identity(value)</code>
    1101. 

  1101.         <br />
    1102. 

  1102.         Returns the same value that is used as the argument. In math:
    1103. 

  1103.         <tt>f(x) = x</tt><br />
    1104. 

  1104.         This function looks useless, but is used throughout Underscore as
    1105. 

  1105.         a default iterator.
    1106. 

  1106.       </p>
    1107. 

  1107.       <pre>
    1108. 

  1108. var moe = {name : 'moe'};
    1109. 

  1109. moe === _.identity(moe);
    1110. 

  1110. =&gt; true</pre>
    1111. 

  1111. 

  1112.       <p id="times">
    1113. 

  1113.         <b class="header">times</b><code>_.times(n, iterator)</code>
    1114. 

  1114.         <br />
    1115. 

  1115.         Invokes the given iterator function <b>n</b> times.
    1116. 

  1116.       </p>
    1117. 

  1117.       <pre>
    1118. 

  1118. _(3).times(function(){ genie.grantWish(); });</pre>
    1119. 

  1119. 

  1120.       <p id="mixin">
    1121. 

  1121.         <b class="header">mixin</b><code>_.mixin(object)</code>
    1122. 

  1122.         <br />
    1123. 

  1123.         Allows you to extend Underscore with your own utility functions. Pass
    1124. 

  1124.         a hash of <tt>{name: function}</tt> definitions to have your functions 
    1125. 

  1125.         added to the Underscore object, as well as the OOP wrapper.
    1126. 

  1126.       </p>
    1127. 

  1127.       <pre>
    1128. 

  1128. _.mixin({
    1129. 

  1129.   capitalize : function(string) {
    1130. 

  1130.     return string.charAt(0).toUpperCase() + string.substring(1).toLowerCase();
    1131. 

  1131.   }
    1132. 

  1132. });
    1133. 

  1133. _("fabio").capitalize();
    1134. 

  1134. =&gt; "Fabio"
    1135. 

  1135. </pre>
    1136. 

  1136. 

  1137.       <p id="uniqueId">
    1138. 

  1138.         <b class="header">uniqueId</b><code>_.uniqueId([prefix])</code>
    1139. 

  1139.         <br />
    1140. 

  1140.         Generate a globally-unique id for client-side models or DOM elements
    1141. 

  1141.         that need one. If <b>prefix</b> is passed, the id will be appended to it.
    1142. 

  1142.       </p>
    1143. 

  1143.       <pre>
    1144. 

  1144. _.uniqueId('contact_');
    1145. 

  1145. =&gt; 'contact_104'</pre>
    1146. 

  1146. 

  1147.       <p id="template">
    1148. 

  1148.         <b class="header">template</b><code>_.template(templateString, [context])</code>
    1149. 

  1149.         <br />
    1150. 

  1150.         Compiles JavaScript templates into functions that can be evaluated
    1151. 

  1151.         for rendering. Useful for rendering complicated bits of HTML from JSON
    1152. 

  1152.         data sources. Template functions can both interpolate variables, using<br />
    1153. 

  1153.         <tt>&lt;%= &hellip; %&gt;</tt>, as well as execute arbitrary JavaScript code, with
    1154. 

  1154.         <tt>&lt;% &hellip; %&gt;</tt>. When you evaluate a template function, pass in a
    1155. 

  1155.         <b>context</b> object that has properties corresponding to the template's free
    1156. 

  1156.         variables. If you're writing a one-off, you can pass the <b>context</b>
    1157. 

  1157.         object as the second parameter to <b>template</b> in order to render
    1158. 

  1158.         immediately instead of returning a template function.
    1159. 

  1159.       </p>
    1160. 

  1160.       <pre>
    1161. 

  1161. var compiled = _.template("hello: &lt;%= name %&gt;");
    1162. 

  1162. compiled({name : 'moe'});
    1163. 

  1163. =&gt; "hello: moe"
    1164. 

  1164. 

  1165. var list = "&lt;% _.each(people, function(name) { %&gt; &lt;li&gt;&lt;%= name %&gt;&lt;/li&gt; &lt;% }); %&gt;";
    1166. 

  1166. _.template(list, {people : ['moe', 'curly', 'larry']});
    1167. 

  1167. =&gt; "&lt;li&gt;moe&lt;/li&gt;&lt;li&gt;curly&lt;/li&gt;&lt;li&gt;larry&lt;/li&gt;"</pre>
    1168. 

  1168. 

  1169.       <p>
    1170. 

  1170.         You can also use <tt>print</tt> from within JavaScript code.  This is
    1171. 

  1171.         sometimes more convenient than using <tt>&lt;%= ... %&gt;</tt>.
    1172. 

  1172.       </p>
    1173. 

  1173.       
    1174. 

  1174.       <pre>
    1175. 

  1175. var compiled = _.template("&lt;% print('Hello ' + epithet); %&gt;");
    1176. 

  1176. compiled({epithet: "stooge"});
    1177. 

  1177. =&gt; "Hello stooge."</pre>
    1178. 

  1178. 

  1179.       <p>
    1180. 

  1180.         If ERB-style delimiters aren't your cup of tea, you can change Underscore's
    1181. 

  1181.         template settings to use different symbols to set off interpolated code.
    1182. 

  1182.         Define an <b>interpolate</b> regex, and an (optional) <b>evaluate</b> regex
    1183. 

  1183.         to match expressions that should be inserted and evaluated, respectively.
    1184. 

  1184.         If no <b>evaluate</b> regex is provided, your templates will only be 
    1185. 

  1185.         capable of interpolating values. 
    1186. 

  1186.         For example, to perform
    1187. 

  1187.         <a href="http://github.com/janl/mustache.js#readme">Mustache.js</a>
    1188. 

  1188.         style templating:
    1189. 

  1189.       </p>
    1190. 

  1190. 

  1191.       <pre>
    1192. 

  1192. _.templateSettings = {
    1193. 

  1193.   interpolate : /\{\{(.+?)\}\}/g
    1194. 

  1194. };
    1195. 

  1195. 

  1196. var template = _.template("Hello {{ name }}!");
    1197. 

  1197. template({name : "Mustache"});
    1198. 

  1198. =&gt; "Hello Mustache!"</pre>
    1199. 

  1199. 

  1200.       <h2>Chaining</h2>
    1201. 

  1201. 

  1202.       <p id="chain">
    1203. 

  1203.         <b class="header">chain</b><code>_(obj).chain()</code>
    1204. 

  1204.         <br />
    1205. 

  1205.         Returns a wrapped object. Calling methods on this object will continue
    1206. 

  1206.         to return wrapped objects until <tt>value</tt> is used. (
    1207. 

  1207.         <a href="#styles">A more realistic example.</a>)
    1208. 

  1208.       </p>
    1209. 

  1209.       <pre>
    1210. 

  1210. var stooges = [{name : 'curly', age : 25}, {name : 'moe', age : 21}, {name : 'larry', age : 23}];
    1211. 

  1211. var youngest = _(stooges).chain()
    1212. 

  1212.   .sortBy(function(stooge){ return stooge.age; })
    1213. 

  1213.   .map(function(stooge){ return stooge.name + ' is ' + stooge.age; })
    1214. 

  1214.   .first()
    1215. 

  1215.   .value();
    1216. 

  1216. =&gt; "moe is 21"
    1217. 

  1217. </pre>
    1218. 

  1218. 

  1219.       <p id="value">
    1220. 

  1220.         <b class="header">value</b><code>_(obj).value()</code>
    1221. 

  1221.         <br />
    1222. 

  1222.         Extracts the value of a wrapped object.
    1223. 

  1223.       </p>
    1224. 

  1224.       <pre>
    1225. 

  1225. _([1, 2, 3]).value();
    1226. 

  1226. =&gt; [1, 2, 3]
    1227. 

  1227. </pre>
    1228. 

  1228. 

  1229.       <h2 id="duck_typing">Duck Typing</h2>
    1230. 

  1230. 

  1231.       <p>
    1232. 

  1232.         The <b>isType</b> (<tt>isArray</tt>, <tt>isFunction</tt>, <tt>isString</tt> ...) family of type-checking
    1233. 

  1233.         functions use property detection to do their work, which, although
    1234. 

  1234.         orders of magnitude faster than the alternative, isn't entirely safe when dealing
    1235. 

  1235.         with objects that are used as hashes, where arbitrary strings are being
    1236. 

  1236.         set for the keys. It's entirely possible for an object to masquerade as
    1237. 

  1237.         another type, if you're setting properties with names like "concat" and
    1238. 

  1238.         "charCodeAt". So be aware.
    1239. 

  1239.       </p>
    1240. 

  1240.       
    1241. 

  1241.       <p>
    1242. 

  1242.         In a similar fashion, <tt>_.each</tt> and all of the other functions 
    1243. 

  1243.         based on it are designed to be able to iterate over any Array-like
    1244. 

  1244.         JavaScript object, including <tt>arguments</tt>, NodeLists, and more.
    1245. 

  1245.         Passing hash-like objects with a numeric <tt>length</tt> key won't work.
    1246. 

  1246.       </p>
    1247. 

  1247. 

  1248. 

  1249.       <h2>Links &amp; Suggested Reading</h2>
    1250. 

  1250. 

  1251.       <p>
    1252. 

  1252.         <a href="http://mirven.github.com/underscore.lua/">Underscore.lua</a>,
    1253. 

  1253.         a Lua port of the functions that are applicable in both languages.
    1254. 

  1254.         Includes OOP-wrapping and chaining.
    1255. 

  1255.         The <a href="http://github.com/mirven/underscore.lua">source</a> is
    1256. 

  1256.         available on GitHub.
    1257. 

  1257.       </p>
    1258. 

  1258.       
    1259. 

  1259.       <p>
    1260. 

  1260.         <a href="http://brianhaveri.github.com/Underscore.php/">Underscore.php</a>,
    1261. 

  1261.         a PHP port of the functions that are applicable in both languages.
    1262. 

  1262.         Includes OOP-wrapping and chaining.
    1263. 

  1263.         The <a href="http://github.com/brianhaveri/Underscore.php">source</a> is
    1264. 

  1264.         available on GitHub.
    1265. 

  1265.       </p>
    1266. 

  1266.       
    1267. 

  1267.       <p>
    1268. 

  1268.         <a href="http://vti.github.com/underscore-perl/">Underscore-perl</a>,
    1269. 

  1269.         a Perl port of many of the Underscore.js functions, 
    1270. 

  1270.         aimed at on Perl hashes and arrays, also 
    1271. 

  1271.         <a href="https://github.com/vti/underscore-perl/">available on GitHub</a>.
    1272. 

  1272.       </p>
    1273. 

  1273.       
    1274. 

  1274.       <p>
    1275. 

  1275.         <a href="https://github.com/edtsech/underscore.string">Underscore.string</a>,
    1276. 

  1276.         an Underscore extension that adds functions for string-manipulation: 
    1277. 

  1277.         <tt>trim</tt>, <tt>startsWith</tt>, <tt>contains</tt>, <tt>capitalize</tt>,
    1278. 

  1278.         <tt>reverse</tt>, <tt>sprintf</tt>, and more.
    1279. 

  1279.       </p>
    1280. 

  1280. 

  1281.       <p>
    1282. 

  1282.         Ruby's <a href="http://ruby-doc.org/core/classes/Enumerable.html">Enumerable</a> module.
    1283. 

  1283.       </p>
    1284. 

  1284. 

  1285.       <p>
    1286. 

  1286.         <a href="http://www.prototypejs.org/">Prototype.js</a>, which provides
    1287. 

  1287.         JavaScript with collection functions in the manner closest to Ruby's Enumerable.
    1288. 

  1288.       </p>
    1289. 

  1289. 

  1290.       <p>
    1291. 

  1291.         Oliver Steele's
    1292. 

  1292.         <a href="http://osteele.com/sources/javascript/functional/">Functional JavaScript</a>,
    1293. 

  1293.         which includes comprehensive higher-order function support as well as string lambdas.
    1294. 

  1294.       </p>
    1295. 

  1295.       
    1296. 

  1296.       <p>
    1297. 

  1297.         Michael Aufreiter's <a href="http://substance.io/#michael/data-js">Data.js</a>,
    1298. 

  1298.         a data manipulation + persistence library for JavaScript.
    1299. 

  1299.       </p>
    1300. 

  1300. 

  1301.       <p>
    1302. 

  1302.         Python's <a href="http://docs.python.org/library/itertools.html">itertools</a>.
    1303. 

  1303.       </p>
    1304. 

  1304. 

  1305.       <h2 id="changelog">Change Log</h2>
    1306. 

  1306.       
    1307. 

  1307.       <p>
    1308. 

  1308.         <b class="header">1.1.7</b> &mdash; <small><i>July 13, 2011</i></small><br />
    1309. 

  1309.         Added <tt>_.groupBy</tt>, which aggregates a collection into groups of like items.
    1310. 

  1310.         Added <tt>_.union</tt> and <tt>_.difference</tt>, to complement the 
    1311. 

  1311.         (re-named) <tt>_.intersection</tt>.
    1312. 

  1312.         Various improvements for support of sparse arrays.
    1313. 

  1313.         <tt>_.toArray</tt> now returns a clone, if directly passed an array.
    1314. 

  1314.         <tt>_.functions</tt> now also returns the names of functions that are present
    1315. 

  1315.         in the prototype chain.
    1316. 

  1316.       </p>
    1317. 

  1317.             
    1318. 

  1318.       <p>
    1319. 

  1319.         <b class="header">1.1.6</b> &mdash; <small><i>April 18, 2011</i></small><br />
    1320. 

  1320.         Added <tt>_.after</tt>, which will return a function that only runs after
    1321. 

  1321.         first being called a specified number of times.
    1322. 

  1322.         <tt>_.invoke</tt> can now take a direct function reference.
    1323. 

  1323.         <tt>_.every</tt> now requires an iterator function to be passed, which
    1324. 

  1324.         mirrors the ECMA5 API.
    1325. 

  1325.         <tt>_.extend</tt> no longer copies keys when the value is undefined.
    1326. 

  1326.         <tt>_.bind</tt> now errors when trying to bind an undefined value.
    1327. 

  1327.       </p>
    1328. 

  1328.       
    1329. 

  1329.       <p>
    1330. 

  1330.         <b class="header">1.1.5</b> &mdash; <small><i>Mar 20, 2011</i></small><br />
    1331. 

  1331.         Added an <tt>_.defaults</tt> function, for use merging together JS objects
    1332. 

  1332.         representing default options.
    1333. 

  1333.         Added an <tt>_.once</tt> function, for manufacturing functions that should
    1334. 

  1334.         only ever execute a single time.
    1335. 

  1335.         <tt>_.bind</tt> now delegates to the native ECMAScript 5 version, 
    1336. 

  1336.         where available.
    1337. 

  1337.         <tt>_.keys</tt> now throws an error when used on non-Object values, as in
    1338. 

  1338.         ECMAScript 5.
    1339. 

  1339.         Fixed a bug with <tt>_.keys</tt> when used over sparse arrays.
    1340. 

  1340.       </p>
    1341. 

  1341.       
    1342. 

  1342.       <p>
    1343. 

  1343.         <b class="header">1.1.4</b> &mdash; <small><i>Jan 9, 2011</i></small><br />
    1344. 

  1344.         Improved compliance with ES5's Array methods when passing <tt>null</tt> 
    1345. 

  1345.         as a value. <tt>_.wrap</tt> now correctly sets <tt>this</tt> for the
    1346. 

  1346.         wrapped function. <tt>_.indexOf</tt> now takes an optional flag for
    1347. 

  1347.         finding the insertion index in an array that is guaranteed to already
    1348. 

  1348.         be sorted. Avoiding the use of <tt>.callee</tt>, to allow <tt>_.isArray</tt>
    1349. 

  1349.         to work properly in ES5's strict mode.
    1350. 

  1350.       </p>
    1351. 

  1351.       
    1352. 

  1352.       <p>
    1353. 

  1353.         <b class="header">1.1.3</b> &mdash; <small><i>Dec 1, 2010</i></small><br />
    1354. 

  1354.         In CommonJS, Underscore may now be required with just: <br />
    1355. 

  1355.         <tt>var _ = require("underscore")</tt>.
    1356. 

  1356.         Added <tt>_.throttle</tt> and <tt>_.debounce</tt> functions.
    1357. 

  1357.         Removed <tt>_.breakLoop</tt>, in favor of an ECMA5-style un-<i>break</i>-able
    1358. 

  1358.         each implementation &mdash; this removes the try/catch, and you'll now have
    1359. 

  1359.         better stack traces for exceptions that are thrown within an Underscore iterator.
    1360. 

  1360.         Improved the <b>isType</b> family of functions for better interoperability
    1361. 

  1361.         with Internet Explorer host objects.
    1362. 

  1362.         <tt>_.template</tt> now correctly escapes backslashes in templates.
    1363. 

  1363.         Improved <tt>_.reduce</tt> compatibility with the ECMA5 version: 
    1364. 

  1364.         if you don't pass an initial value, the first item in the collection is used.
    1365. 

  1365.         <tt>_.each</tt> no longer returns the iterated collection, for improved
    1366. 

  1366.         consistency with ES5's <tt>forEach</tt>.
    1367. 

  1367.       </p>
    1368. 

  1368.       
    1369. 

  1369.       <p>
    1370. 

  1370.         <b class="header">1.1.2</b><br />
    1371. 

  1371.         Fixed <tt>_.contains</tt>, which was mistakenly pointing at 
    1372. 

  1372.         <tt>_.intersect</tt> instead of <tt>_.include</tt>, like it should 
    1373. 

  1373.         have been. Added <tt>_.unique</tt> as an alias for <tt>_.uniq</tt>.
    1374. 

  1374.       </p>
    1375. 

  1375.       
    1376. 

  1376.       <p>
    1377. 

  1377.         <b class="header">1.1.1</b><br />
    1378. 

  1378.         Improved the speed of <tt>_.template</tt>, and its handling of multiline
    1379. 

  1379.         interpolations. Ryan Tenney contributed optimizations to many Underscore 
    1380. 

  1380.         functions. An annotated version of the source code is now available.
    1381. 

  1381.       </p>
    1382. 

  1382.       
    1383. 

  1383.       <p>
    1384. 

  1384.         <b class="header">1.1.0</b><br />
    1385. 

  1385.         The method signature of <tt>_.reduce</tt> has been changed to match
    1386. 

  1386.         the ECMAScript 5 signature, instead of the Ruby/Prototype.js version.
    1387. 

  1387.         This is a backwards-incompatible change. <tt>_.template</tt> may now be
    1388. 

  1388.         called with no arguments, and preserves whitespace. <tt>_.contains</tt>
    1389. 

  1389.         is a new alias for <tt>_.include</tt>.
    1390. 

  1390.       </p>
    1391. 

  1391.       
    1392. 

  1392.       <p>
    1393. 

  1393.         <b class="header">1.0.4</b><br />
    1394. 

  1394.         <a href="http://themoell.com/">Andri Möll</a> contributed the <tt>_.memoize</tt> 
    1395. 

  1395.         function, which can be used to speed up expensive repeated computations 
    1396. 

  1396.         by caching the results.
    1397. 

  1397.       </p>
    1398. 

  1398.       
    1399. 

  1399.       <p>
    1400. 

  1400.         <b class="header">1.0.3</b><br />
    1401. 

  1401.         Patch that makes <tt>_.isEqual</tt> return <tt>false</tt> if any property
    1402. 

  1402.         of the compared object has a <tt>NaN</tt> value. Technically the correct
    1403. 

  1403.         thing to do, but of questionable semantics. Watch out for NaN comparisons.
    1404. 

  1404.       </p>
    1405. 

  1405.       
    1406. 

  1406.       <p>
    1407. 

  1407.         <b class="header">1.0.2</b><br />
    1408. 

  1408.         Fixes <tt>_.isArguments</tt> in recent versions of Opera, which have
    1409. 

  1409.         arguments objects as real Arrays.
    1410. 

  1410.       </p>
    1411. 

  1411.       
    1412. 

  1412.       <p>
    1413. 

  1413.         <b class="header">1.0.1</b><br />
    1414. 

  1414.         Bugfix for <tt>_.isEqual</tt>, when comparing two objects with the same 
    1415. 

  1415.         number of undefined keys, but with different names.
    1416. 

  1416.       </p>
    1417. 

  1417.       
    1418. 

  1418.       <p>
    1419. 

  1419.         <b class="header">1.0.0</b><br />
    1420. 

  1420.         Things have been stable for many months now, so Underscore is now
    1421. 

  1421.         considered to be out of beta, at <b>1.0</b>. Improvements since <b>0.6</b>
    1422. 

  1422.         include <tt>_.isBoolean</tt>, and the ability to have <tt>_.extend</tt>
    1423. 

  1423.         take multiple source objects.
    1424. 

  1424.       </p>
    1425. 

  1425.       
    1426. 

  1426.       <p>
    1427. 

  1427.         <b class="header">0.6.0</b><br />
    1428. 

  1428.         Major release. Incorporates a number of 
    1429. 

  1429.         <a href="http://github.com/ratbeard">Mile Frawley's</a> refactors for
    1430. 

  1430.         safer duck-typing on collection functions, and cleaner internals. A new
    1431. 

  1431.         <tt>_.mixin</tt> method that allows you to extend Underscore with utility
    1432. 

  1432.         functions of your own. Added <tt>_.times</tt>, which works the same as in 
    1433. 

  1433.         Ruby or Prototype.js. Native support for ECMAScript 5's <tt>Array.isArray</tt>, 
    1434. 

  1434.         and <tt>Object.keys</tt>.
    1435. 

  1435.       </p>
    1436. 

  1436. 

  1437.       <p>
    1438. 

  1438.         <b class="header">0.5.8</b><br />
    1439. 

  1439.         Fixed Underscore's collection functions to work on
    1440. 

  1440.         <a href="https://developer.mozilla.org/En/DOM/NodeList">NodeLists</a> and
    1441. 

  1441.         <a href="https://developer.mozilla.org/En/DOM/HTMLCollection">HTMLCollections</a>
    1442. 

  1442.         once more, thanks to
    1443. 

  1443.         <a href="http://github.com/jmtulloss">Justin Tulloss</a>.
    1444. 

  1444.       </p>
    1445. 

  1445. 

  1446.       <p>
    1447. 

  1447.         <b class="header">0.5.7</b><br />
    1448. 

  1448.         A safer implementation of <tt>_.isArguments</tt>, and a
    1449. 

  1449.         faster <tt>_.isNumber</tt>,<br />thanks to
    1450. 

  1450.         <a href="http://jedschmidt.com/">Jed Schmidt</a>.
    1451. 

  1451.       </p>
    1452. 

  1452. 

  1453.       <p>
    1454. 

  1454.         <b class="header">0.5.6</b><br />
    1455. 

  1455.         Customizable delimiters for <tt>_.template</tt>, contributed by
    1456. 

  1456.         <a href="http://github.com/iamnoah">Noah Sloan</a>.
    1457. 

  1457.       </p>
    1458. 

  1458. 

  1459.       <p>
    1460. 

  1460.         <b class="header">0.5.5</b><br />
    1461. 

  1461.         Fix for a bug in MobileSafari's OOP-wrapper, with the arguments object.
    1462. 

  1462.       </p>
    1463. 

  1463. 

  1464.       <p>
    1465. 

  1465.         <b class="header">0.5.4</b><br />
    1466. 

  1466.         Fix for multiple single quotes within a template string for
    1467. 

  1467.         <tt>_.template</tt>. See:
    1468. 

  1468.         <a href="http://www.west-wind.com/Weblog/posts/509108.aspx">Rick Strahl's blog post</a>.
    1469. 

  1469.       </p>
    1470. 

  1470. 

  1471.       <p>
    1472. 

  1472.         <b class="header">0.5.2</b><br />
    1473. 

  1473.         New implementations of <tt>isArray</tt>, <tt>isDate</tt>, <tt>isFunction</tt>,
    1474. 

  1474.         <tt>isNumber</tt>, <tt>isRegExp</tt>, and <tt>isString</tt>, thanks to
    1475. 

  1475.         a suggestion from
    1476. 

  1476.         <a href="http://www.broofa.com/">Robert Kieffer</a>.
    1477. 

  1477.         Instead of doing <tt>Object#toString</tt>
    1478. 

  1478.         comparisons, they now check for expected properties, which is less safe,
    1479. 

  1479.         but more than an order of magnitude faster. Most other Underscore
    1480. 

  1480.         functions saw minor speed improvements as a result.
    1481. 

  1481.         <a href="http://dolzhenko.org/">Evgeniy Dolzhenko</a>
    1482. 

  1482.         contributed <tt>_.tap</tt>,
    1483. 

  1483.         <a href="http://ruby-doc.org/core-1.9/classes/Object.html#M000191">similar to Ruby 1.9's</a>,
    1484. 

  1484.         which is handy for injecting side effects (like logging) into chained calls.
    1485. 

  1485.       </p>
    1486. 

  1486. 

  1487.       <p>
    1488. 

  1488.         <b class="header">0.5.1</b><br />
    1489. 

  1489.         Added an <tt>_.isArguments</tt> function. Lots of little safety checks
    1490. 

  1490.         and optimizations contributed by
    1491. 

  1491.         <a href="http://github.com/iamnoah/">Noah Sloan</a> and 
    1492. 

  1492.         <a href="http://themoell.com/">Andri Möll</a>.
    1493. 

  1493.       </p>
    1494. 

  1494. 

  1495.       <p>
    1496. 

  1496.         <b class="header">0.5.0</b><br />
    1497. 

  1497.         <b>[API Changes]</b> <tt>_.bindAll</tt> now takes the context object as
    1498. 

  1498.         its first parameter. If no method names are passed, all of the context
    1499. 

  1499.         object's methods are bound to it, enabling chaining and easier binding.
    1500. 

  1500.         <tt>_.functions</tt> now takes a single argument and returns the names
    1501. 

  1501.         of its Function properties. Calling <tt>_.functions(_)</tt> will get you
    1502. 

  1502.         the previous behavior.
    1503. 

  1503.         Added <tt>_.isRegExp</tt> so that <tt>isEqual</tt> can now test for RegExp equality.
    1504. 

  1504.         All of the "is" functions have been shrunk down into a single definition.
    1505. 

  1505.         <a href="http://github.com/grayrest/">Karl Guertin</a> contributed patches.
    1506. 

  1506.       </p>
    1507. 

  1507. 

  1508.       <p>
    1509. 

  1509.         <b class="header">0.4.7</b><br />
    1510. 

  1510.         Added <tt>isDate</tt>, <tt>isNaN</tt>, and <tt>isNull</tt>, for completeness.
    1511. 

  1511.         Optimizations for <tt>isEqual</tt> when checking equality between Arrays
    1512. 

  1512.         or Dates. <tt>_.keys</tt> is now <small><i><b>25%&ndash;2X</b></i></small> faster (depending on your
    1513. 

  1513.         browser) which speeds up the functions that rely on it, such as <tt>_.each</tt>.
    1514. 

  1514.       </p>
    1515. 

  1515. 

  1516.       <p>
    1517. 

  1517.         <b class="header">0.4.6</b><br />
    1518. 

  1518.         Added the <tt>range</tt> function, a port of the
    1519. 

  1519.         <a href="http://docs.python.org/library/functions.html#range">Python
    1520. 

  1520.         function of the same name</a>, for generating flexibly-numbered lists
    1521. 

  1521.         of integers. Original patch contributed by
    1522. 

  1522.         <a href="http://github.com/kylichuku">Kirill Ishanov</a>.
    1523. 

  1523.       </p>
    1524. 

  1524. 

  1525.       <p>
    1526. 

  1526.         <b class="header">0.4.5</b><br />
    1527. 

  1527.         Added <tt>rest</tt> for Arrays and arguments objects, and aliased
    1528. 

  1528.         <tt>first</tt> as <tt>head</tt>, and <tt>rest</tt> as <tt>tail</tt>,
    1529. 

  1529.         thanks to <a href="http://github.com/lukesutton/">Luke Sutton</a>'s patches.
    1530. 

  1530.         Added tests ensuring that all Underscore Array functions also work on
    1531. 

  1531.         <i>arguments</i> objects.
    1532. 

  1532.       </p>
    1533. 

  1533. 

  1534.       <p>
    1535. 

  1535.         <b class="header">0.4.4</b><br />
    1536. 

  1536.         Added <tt>isString</tt>, and <tt>isNumber</tt>, for consistency. Fixed
    1537. 

  1537.         <tt>_.isEqual(NaN, NaN)</tt> to return <i>true</i> (which is debatable).
    1538. 

  1538.       </p>
    1539. 

  1539. 

  1540.       <p>
    1541. 

  1541.         <b class="header">0.4.3</b><br />
    1542. 

  1542.         Started using the native <tt>StopIteration</tt> object in browsers that support it.
    1543. 

  1543.         Fixed Underscore setup for CommonJS environments.
    1544. 

  1544.       </p>
    1545. 

  1545. 

  1546.       <p>
    1547. 

  1547.         <b class="header">0.4.2</b><br />
    1548. 

  1548.         Renamed the unwrapping function to <tt>value</tt>, for clarity.
    1549. 

  1549.       </p>
    1550. 

  1550. 

  1551.       <p>
    1552. 

  1552.         <b class="header">0.4.1</b><br />
    1553. 

  1553.         Chained Underscore objects now support the Array prototype methods, so
    1554. 

  1554.         that you can perform the full range of operations on a wrapped array
    1555. 

  1555.         without having to break your chain. Added a <tt>breakLoop</tt> method
    1556. 

  1556.         to <b>break</b> in the middle of any Underscore iteration. Added an
    1557. 

  1557.         <tt>isEmpty</tt> function that works on arrays and objects.
    1558. 

  1558.       </p>
    1559. 

  1559. 

  1560.       <p>
    1561. 

  1561.         <b class="header">0.4.0</b><br />
    1562. 

  1562.         All Underscore functions can now be called in an object-oriented style,
    1563. 

  1563.         like so: <tt>_([1, 2, 3]).map(...);</tt>. Original patch provided by
    1564. 

  1564.         <a href="http://macournoyer.com/">Marc-André Cournoyer</a>.
    1565. 

  1565.         Wrapped objects can be chained through multiple
    1566. 

  1566.         method invocations. A <a href="#functions"><tt>functions</tt></a> method
    1567. 

  1567.         was added, providing a sorted list of all the functions in Underscore.
    1568. 

  1568.       </p>
    1569. 

  1569. 

  1570.       <p>
    1571. 

  1571.         <b class="header">0.3.3</b><br />
    1572. 

  1572.         Added the JavaScript 1.8 function <tt>reduceRight</tt>. Aliased it
    1573. 

  1573.         as <tt>foldr</tt>, and aliased <tt>reduce</tt> as <tt>foldl</tt>.
    1574. 

  1574.       </p>
    1575. 

  1575. 

  1576.       <p>
    1577. 

  1577.         <b class="header">0.3.2</b><br />
    1578. 

  1578.         Now runs on stock <a href="http://www.mozilla.org/rhino/">Rhino</a>
    1579. 

  1579.         interpreters with: <tt>load("underscore.js")</tt>.
    1580. 

  1580.         Added <a href="#identity"><tt>identity</tt></a> as a utility function.
    1581. 

  1581.       </p>
    1582. 

  1582. 

  1583.       <p>
    1584. 

  1584.         <b class="header">0.3.1</b><br />
    1585. 

  1585.         All iterators are now passed in the original collection as their third
    1586. 

  1586.         argument, the same as JavaScript 1.6's <b>forEach</b>. Iterating over
    1587. 

  1587.         objects is now called with <tt>(value, key, collection)</tt>, for details
    1588. 

  1588.         see <a href="#each"><tt>_.each</tt></a>.
    1589. 

  1589.       </p>
    1590. 

  1590. 

  1591.       <p>
    1592. 

  1592.         <b class="header">0.3.0</b><br />
    1593. 

  1593.         Added <a href="http://github.com/dmitryBaranovskiy">Dmitry Baranovskiy</a>'s
    1594. 

  1594.         comprehensive optimizations, merged in
    1595. 

  1595.         <a href="http://github.com/kriskowal/">Kris Kowal</a>'s patches to make Underscore
    1596. 

  1596.         <a href="http://wiki.commonjs.org/wiki/CommonJS">CommonJS</a> and
    1597. 

  1597.         <a href="http://narwhaljs.org/">Narwhal</a> compliant.
    1598. 

  1598.       </p>
    1599. 

  1599. 

  1600.       <p>
    1601. 

  1601.         <b class="header">0.2.0</b><br />
    1602. 

  1602.         Added <tt>compose</tt> and <tt>lastIndexOf</tt>, renamed <tt>inject</tt> to
    1603. 

  1603.         <tt>reduce</tt>, added aliases for <tt>inject</tt>, <tt>filter</tt>,
    1604. 

  1604.         <tt>every</tt>, <tt>some</tt>, and <tt>forEach</tt>.
    1605. 

  1605.       </p>
    1606. 

  1606. 

  1607.       <p>
    1608. 

  1608.         <b class="header">0.1.1</b><br />
    1609. 

  1609.         Added <tt>noConflict</tt>, so that the "Underscore" object can be assigned to
    1610. 

  1610.         other variables.
    1611. 

  1611.       </p>
    1612. 

  1612. 

  1613.       <p>
    1614. 

  1614.         <b class="header">0.1.0</b><br />
    1615. 

  1615.         Initial release of Underscore.js.
    1616. 

  1616.       </p>
    1617. 

  1617. 

  1618.       <p>
    1619. 

  1619.         <a href="http://documentcloud.org/" title="A DocumentCloud Project" style="background:none;">
    1620. 

  1620.           <img src="http://jashkenas.s3.amazonaws.com/images/a_documentcloud_project.png" alt="A DocumentCloud Project" />
    1621. 

  1621.         </a>
    1622. 

  1622.       </p>
    1623. 

  1623. 

  1624.     </div>
    1625. 

  1625. 

  1626.   </div>
    1627. 

  1627. 

  1628.   <!-- Include Underscore, so you can play with it in the console. -->
    1629. 

  1629.   <script type="text/javascript" src="underscore.js"></script>
    1630. 

  1630. 

  1631. </body>
    1632. 

  1632. </html>
    1633. 

  1633.