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    175. 

  175.   </style>
    176. 

  176. </head>
    177. 

  177. <body>
    178. 

  178. 

  179.   <div id="sidebar" class="interface">
    180. 

  180. 

  181.     <a class="toc_title" href="#">
    182. 

  182.       Underscore.js <span class="version">(1.4.2)</span>
    183. 

  183.     </a>
    184. 

  184. 

  185.     <a class="toc_title" href="#">
    186. 

  186.       Introduction
    187. 

  187.     </a>
    188. 

  188. 

  189.     <a class="toc_title" href="#collections">
    190. 

  190.       Collections
    191. 

  191.     </a>
    192. 

  192.     <ul class="toc_section">
    193. 

  193.       <li>- <a href="#each">each</a></li>
    194. 

  194.       <li>- <a href="#map">map</a></li>
    195. 

  195.       <li>- <a href="#reduce">reduce</a></li>
    196. 

  196.       <li>- <a href="#reduceRight">reduceRight</a></li>
    197. 

  197.       <li>- <a href="#find">find</a></li>
    198. 

  198.       <li>- <a href="#filter">filter</a></li>
    199. 

  199.       <li>- <a href="#where">where</a></li>
    200. 

  200.       <li>- <a href="#reject">reject</a></li>
    201. 

  201.       <li>- <a href="#every">every</a></li>
    202. 

  202.       <li>- <a href="#some">some</a></li>
    203. 

  203.       <li>- <a href="#contains">contains</a></li>
    204. 

  204.       <li>- <a href="#invoke">invoke</a></li>
    205. 

  205.       <li>- <a href="#pluck">pluck</a></li>
    206. 

  206.       <li>- <a href="#max">max</a></li>
    207. 

  207.       <li>- <a href="#min">min</a></li>
    208. 

  208.       <li>- <a href="#sortBy">sortBy</a></li>
    209. 

  209.       <li>- <a href="#groupBy">groupBy</a></li>
    210. 

  210.       <li>- <a href="#countBy">countBy</a></li>
    211. 

  211.       <li>- <a href="#shuffle">shuffle</a></li>
    212. 

  212.       <li>- <a href="#toArray">toArray</a></li>
    213. 

  213.       <li>- <a href="#size">size</a></li>
    214. 

  214.     </ul>
    215. 

  215. 

  216.     <a class="toc_title" href="#arrays">
    217. 

  217.       Arrays
    218. 

  218.     </a>
    219. 

  219.     <ul class="toc_section">
    220. 

  220.       <li>- <a href="#first">first</a></li>
    221. 

  221.       <li>- <a href="#initial">initial</a></li>
    222. 

  222.       <li>- <a href="#last">last</a></li>
    223. 

  223.       <li>- <a href="#rest">rest</a></li>
    224. 

  224.       <li>- <a href="#compact">compact</a></li>
    225. 

  225.       <li>- <a href="#flatten">flatten</a></li>
    226. 

  226.       <li>- <a href="#without">without</a></li>
    227. 

  227.       <li>- <a href="#union">union</a></li>
    228. 

  228.       <li>- <a href="#intersection">intersection</a></li>
    229. 

  229.       <li>- <a href="#difference">difference</a></li>
    230. 

  230.       <li>- <a href="#uniq">uniq</a></li>
    231. 

  231.       <li>- <a href="#zip">zip</a></li>
    232. 

  232.       <li>- <a href="#object">object</a></li>
    233. 

  233.       <li>- <a href="#indexOf">indexOf</a></li>
    234. 

  234.       <li>- <a href="#lastIndexOf">lastIndexOf</a></li>
    235. 

  235.       <li>- <a href="#sortedIndex">sortedIndex</a></li>
    236. 

  236.       <li>- <a href="#range">range</a></li>
    237. 

  237.     </ul>
    238. 

  238. 

  239.     <a class="toc_title" href="#functions">
    240. 

  240.       Functions
    241. 

  241.     </a>
    242. 

  242.     <ul class="toc_section">
    243. 

  243.       <li>- <a href="#bind">bind</a></li>
    244. 

  244.       <li>- <a href="#bindAll">bindAll</a></li>
    245. 

  245.       <li>- <a href="#memoize">memoize</a></li>
    246. 

  246.       <li>- <a href="#delay">delay</a></li>
    247. 

  247.       <li>- <a href="#defer">defer</a></li>
    248. 

  248.       <li>- <a href="#throttle">throttle</a></li>
    249. 

  249.       <li>- <a href="#debounce">debounce</a></li>
    250. 

  250.       <li>- <a href="#once">once</a></li>
    251. 

  251.       <li>- <a href="#after">after</a></li>
    252. 

  252.       <li>- <a href="#wrap">wrap</a></li>
    253. 

  253.       <li>- <a href="#compose">compose</a></li>
    254. 

  254.     </ul>
    255. 

  255. 

  256.     <a class="toc_title" href="#objects">
    257. 

  257.       Objects
    258. 

  258.     </a>
    259. 

  259.     <ul class="toc_section">
    260. 

  260.       <li>- <a href="#keys">keys</a></li>
    261. 

  261.       <li>- <a href="#values">values</a></li>
    262. 

  262.       <li>- <a href="#pairs">pairs</a></li>
    263. 

  263.       <li>- <a href="#invert">invert</a></li>
    264. 

  264.       <li>- <a href="#object-functions">functions</a></li>
    265. 

  265.       <li>- <a href="#extend">extend</a></li>
    266. 

  266.       <li>- <a href="#pick">pick</a></li>
    267. 

  267.       <li>- <a href="#omit">omit</a></li>
    268. 

  268.       <li>- <a href="#defaults">defaults</a></li>
    269. 

  269.       <li>- <a href="#clone">clone</a></li>
    270. 

  270.       <li>- <a href="#tap">tap</a></li>
    271. 

  271.       <li>- <a href="#has">has</a></li>
    272. 

  272.       <li>- <a href="#isEqual">isEqual</a></li>
    273. 

  273.       <li>- <a href="#isEmpty">isEmpty</a></li>
    274. 

  274.       <li>- <a href="#isElement">isElement</a></li>
    275. 

  275.       <li>- <a href="#isArray">isArray</a></li>
    276. 

  276.       <li>- <a href="#isObject">isObject</a></li>
    277. 

  277.       <li>- <a href="#isArguments">isArguments</a></li>
    278. 

  278.       <li>- <a href="#isFunction">isFunction</a></li>
    279. 

  279.       <li>- <a href="#isString">isString</a></li>
    280. 

  280.       <li>- <a href="#isNumber">isNumber</a></li>
    281. 

  281.       <li>- <a href="#isFinite">isFinite</a></li>
    282. 

  282.       <li>- <a href="#isBoolean">isBoolean</a></li>
    283. 

  283.       <li>- <a href="#isDate">isDate</a></li>
    284. 

  284.       <li>- <a href="#isRegExp">isRegExp</a></li>
    285. 

  285.       <li>- <a href="#isNaN">isNaN</a></li>
    286. 

  286.       <li>- <a href="#isNull">isNull</a></li>
    287. 

  287.       <li>- <a href="#isUndefined">isUndefined</a></li>
    288. 

  288.     </ul>
    289. 

  289. 

  290.     <a class="toc_title" href="#utility">
    291. 

  291.       Utility
    292. 

  292.     </a>
    293. 

  293.     <ul class="toc_section">
    294. 

  294.       <li>- <a href="#noConflict">noConflict</a></li>
    295. 

  295.       <li>- <a href="#identity">identity</a></li>
    296. 

  296.       <li>- <a href="#times">times</a></li>
    297. 

  297.       <li>- <a href="#random">random</a></li>
    298. 

  298.       <li>- <a href="#mixin">mixin</a></li>
    299. 

  299.       <li>- <a href="#uniqueId">uniqueId</a></li>
    300. 

  300.       <li>- <a href="#escape">escape</a></li>
    301. 

  301.       <li>- <a href="#unescape">unescape</a></li>
    302. 

  302.       <li>- <a href="#result">result</a></li>
    303. 

  303.       <li>- <a href="#template">template</a></li>
    304. 

  304.     </ul>
    305. 

  305. 

  306.     <a class="toc_title" href="#chaining">
    307. 

  307.       Chaining
    308. 

  308.     </a>
    309. 

  309.     <ul class="toc_section">
    310. 

  310.       <li>- <a href="#chain">chain</a></li>
    311. 

  311.       <li>- <a href="#value">value</a></li>
    312. 

  312.     </ul>
    313. 

  313. 

  314.     <a class="toc_title" href="#links">
    315. 

  315.       Links
    316. 

  316.     </a>
    317. 

  317. 

  318.     <a class="toc_title" href="#changelog">
    319. 

  319.       Change Log
    320. 

  320.     </a>
    321. 

  321. 

  322.   </div>
    323. 

  323. 

  324.   <div class="container">
    325. 

  325. 

  326.     <p id="introduction">
    327. 

  327.       <img id="logo" src="docs/images/underscore.png" alt="Underscore.js" />
    328. 

  328.     </p>
    329. 

  329. 

  330.     <p>
    331. 

  331.       <a href="http://github.com/documentcloud/underscore/">Underscore</a> is a
    332. 

  332.       utility-belt library for JavaScript that provides a lot of the
    333. 

  333.       functional programming support that you would expect in
    334. 

  334.       <a href="http://prototypejs.org/api">Prototype.js</a>
    335. 

  335.       (or <a href="http://www.ruby-doc.org/core/classes/Enumerable.html">Ruby</a>),
    336. 

  336.       but without extending any of the built-in JavaScript objects. It's the
    337. 

  337.       tie to go along with <a href="http://docs.jquery.com">jQuery</a>'s tux,
    338. 

  338.       and <a href="http://backbonejs.org">Backbone.js</a>'s suspenders.
    339. 

  339.     </p>
    340. 

  340. 

  341.     <p>
    342. 

  342.       Underscore provides 80-odd functions that support both the usual
    343. 

  343.       functional suspects: <b>map</b>, <b>select</b>, <b>invoke</b> &mdash;
    344. 

  344.       as well as more specialized helpers: function binding, javascript
    345. 

  345.       templating, deep equality testing, and so on. It delegates to built-in
    346. 

  346.       functions, if present, so modern browsers will use the
    347. 

  347.       native implementations of <b>forEach</b>, <b>map</b>, <b>reduce</b>,
    348. 

  348.       <b>filter</b>, <b>every</b>, <b>some</b> and <b>indexOf</b>.
    349. 

  349.     </p>
    350. 

  350. 

  351.     <p>
    352. 

  352.       A complete <a href="test/">Test &amp; Benchmark Suite</a>
    353. 

  353.       is included for your perusal.
    354. 

  354.     </p>
    355. 

  355. 

  356.     <p>
    357. 

  357.       You may also read through the <a href="docs/underscore.html">annotated source code</a>.
    358. 

  358.     </p>
    359. 

  359. 

  360.     <p>
    361. 

  361.       The project is
    362. 

  362.       <a href="http://github.com/documentcloud/underscore/">hosted on GitHub</a>.
    363. 

  363.       You can report bugs and discuss features on the
    364. 

  364.       <a href="http://github.com/documentcloud/underscore/issues">issues page</a>,
    365. 

  365.       on Freenode in the <tt>#documentcloud</tt> channel,
    366. 

  366.       or send tweets to <a href="http://twitter.com/documentcloud">@documentcloud</a>.
    367. 

  367.     </p>
    368. 

  368. 

  369.     <p>
    370. 

  370.       <i>Underscore is an open-source component of <a href="http://documentcloud.org/">DocumentCloud</a>.</i>
    371. 

  371.     </p>
    372. 

  372. 

  373.     <h2>Downloads <i style="padding-left: 12px; font-size:12px;">(Right-click, and use "Save As")</i></h2>
    374. 

  374. 

  375.     <table>
    376. 

  376.       <tr>
    377. 

  377.         <td><a href="underscore.js">Development Version (1.4.2)</a></td>
    378. 

  378.         <td><i>40kb, Uncompressed with Plentiful Comments</i></td>
    379. 

  379.       </tr>
    380. 

  380.       <tr>
    381. 

  381.         <td><a href="underscore-min.js">Production Version (1.4.2)</a></td>
    382. 

  382.         <td><i>4kb, Minified and Gzipped</i></td>
    383. 

  383.       </tr>
    384. 

  384.       <tr>
    385. 

  385.         <td colspan="2"><div class="rule"></div></td>
    386. 

  386.       </tr>
    387. 

  387.       <tr>
    388. 

  388.         <td><a href="https://raw.github.com/documentcloud/underscore/master/underscore.js">Edge Version</a></td>
    389. 

  389.         <td><i>Unreleased, current <tt>master</tt>, use at your own risk</i></td>
    390. 

  390.       </tr>
    391. 

  391.     </table>
    392. 

  392. 

  393.     <div id="documentation">
    394. 

  394. 

  395.       <h2 id="collections">Collection Functions (Arrays or Objects)</h2>
    396. 

  396. 

  397.       <p id="each">
    398. 

  398.         <b class="header">each</b><code>_.each(list, iterator, [context])</code>
    399. 

  399.         <span class="alias">Alias: <b>forEach</b></span>
    400. 

  400.         <br />
    401. 

  401.         Iterates over a <b>list</b> of elements, yielding each in turn to an <b>iterator</b>
    402. 

  402.         function. The <b>iterator</b> is bound to the <b>context</b> object, if one is
    403. 

  403.         passed. Each invocation of <b>iterator</b> is called with three arguments:
    404. 

  404.         <tt>(element, index, list)</tt>. If <b>list</b> is a JavaScript object, <b>iterator</b>'s
    405. 

  405.         arguments will be <tt>(value, key, list)</tt>. Delegates to the native
    406. 

  406.         <b>forEach</b> function if it exists.
    407. 

  407.       </p>
    408. 

  408.       <pre>
    409. 

  409. _.each([1, 2, 3], function(num){ alert(num); });
    410. 

  410. =&gt; alerts each number in turn...
    411. 

  411. _.each({one : 1, two : 2, three : 3}, function(num, key){ alert(num); });
    412. 

  412. =&gt; alerts each number in turn...</pre>
    413. 

  413. 

  414.       <p id="map">
    415. 

  415.         <b class="header">map</b><code>_.map(list, iterator, [context])</code>
    416. 

  416.         <span class="alias">Alias: <b>collect</b></span>
    417. 

  417.         <br />
    418. 

  418.         Produces a new array of values by mapping each value in <b>list</b>
    419. 

  419.         through a transformation function (<b>iterator</b>). If the native <b>map</b> method
    420. 

  420.         exists, it will be used instead. If <b>list</b> is a JavaScript object,
    421. 

  421.         <b>iterator</b>'s arguments will be <tt>(value, key, list)</tt>.
    422. 

  422.       </p>
    423. 

  423.       <pre>
    424. 

  424. _.map([1, 2, 3], function(num){ return num * 3; });
    425. 

  425. =&gt; [3, 6, 9]
    426. 

  426. _.map({one : 1, two : 2, three : 3}, function(num, key){ return num * 3; });
    427. 

  427. =&gt; [3, 6, 9]</pre>
    428. 

  428. 

  429.       <p id="reduce">
    430. 

  430.         <b class="header">reduce</b><code>_.reduce(list, iterator, memo, [context])</code>
    431. 

  431.         <span class="alias">Aliases: <b>inject, foldl</b></span>
    432. 

  432.         <br />
    433. 

  433.         Also known as <b>inject</b> and <b>foldl</b>, <b>reduce</b> boils down a
    434. 

  434.         <b>list</b> of values into a single value. <b>Memo</b> is the initial state
    435. 

  435.         of the reduction, and each successive step of it should be returned by
    436. 

  436.         <b>iterator</b>. The iterator is passed four arguments: the <tt>memo</tt>,
    437. 

  437.         then the <tt>value</tt> and <tt>index</tt> (or key) of the iteration,
    438. 

  438.         and finally a reference to the entire <tt>list</tt>.
    439. 

  439.       </p>
    440. 

  440.       <pre>
    441. 

  441. var sum = _.reduce([1, 2, 3], function(memo, num){ return memo + num; }, 0);
    442. 

  442. =&gt; 6
    443. 

  443. </pre>
    444. 

  444. 

  445.       <p id="reduceRight">
    446. 

  446.         <b class="header">reduceRight</b><code>_.reduceRight(list, iterator, memo, [context])</code>
    447. 

  447.         <span class="alias">Alias: <b>foldr</b></span>
    448. 

  448.         <br />
    449. 

  449.         The right-associative version of <b>reduce</b>. Delegates to the
    450. 

  450.         JavaScript 1.8 version of <b>reduceRight</b>, if it exists. <b>Foldr</b>
    451. 

  451.         is not as useful in JavaScript as it would be in a language with lazy
    452. 

  452.         evaluation.
    453. 

  453.       </p>
    454. 

  454.       <pre>
    455. 

  455. var list = [[0, 1], [2, 3], [4, 5]];
    456. 

  456. var flat = _.reduceRight(list, function(a, b) { return a.concat(b); }, []);
    457. 

  457. =&gt; [4, 5, 2, 3, 0, 1]
    458. 

  458. </pre>
    459. 

  459. 

  460.       <p id="find">
    461. 

  461.         <b class="header">find</b><code>_.find(list, iterator, [context])</code>
    462. 

  462.         <span class="alias">Alias: <b>detect</b></span>
    463. 

  463.         <br />
    464. 

  464.         Looks through each value in the <b>list</b>, returning the first one that
    465. 

  465.         passes a truth test (<b>iterator</b>). The function returns as
    466. 

  466.         soon as it finds an acceptable element, and doesn't traverse the
    467. 

  467.         entire list.
    468. 

  468.       </p>
    469. 

  469.       <pre>
    470. 

  470. var even = _.find([1, 2, 3, 4, 5, 6], function(num){ return num % 2 == 0; });
    471. 

  471. =&gt; 2
    472. 

  472. </pre>
    473. 

  473. 

  474.       <p id="filter">
    475. 

  475.         <b class="header">filter</b><code>_.filter(list, iterator, [context])</code>
    476. 

  476.         <span class="alias">Alias: <b>select</b></span>
    477. 

  477.         <br />
    478. 

  478.         Looks through each value in the <b>list</b>, returning an array of all
    479. 

  479.         the values that pass a truth test (<b>iterator</b>). Delegates to the
    480. 

  480.         native <b>filter</b> method, if it exists.
    481. 

  481.       </p>
    482. 

  482.       <pre>
    483. 

  483. var evens = _.filter([1, 2, 3, 4, 5, 6], function(num){ return num % 2 == 0; });
    484. 

  484. =&gt; [2, 4, 6]
    485. 

  485. </pre>
    486. 

  486. 

  487.       <p id="where">
    488. 

  488.         <b class="header">where</b><code>_.where(list, properties)</code>
    489. 

  489.         <br />
    490. 

  490.         Looks through each value in the <b>list</b>, returning an array of all
    491. 

  491.         the values that contain all of the key-value pairs listed in <b>properties</b>.
    492. 

  492.       </p>
    493. 

  493.       <pre>
    494. 

  494. _.where(listOfPlays, {author: "Shakespeare", year: 1611});
    495. 

  495. =&gt; [{title: "Cymbeline", author: "Shakespeare", year: 1611},
    496. 

  496.     {title: "The Tempest", author: "Shakespeare", year: 1611}]
    497. 

  497. </pre>
    498. 

  498. 

  499.       <p id="reject">
    500. 

  500.         <b class="header">reject</b><code>_.reject(list, iterator, [context])</code>
    501. 

  501.         <br />
    502. 

  502.         Returns the values in <b>list</b> without the elements that the truth
    503. 

  503.         test (<b>iterator</b>) passes. The opposite of <b>filter</b>.
    504. 

  504.       </p>
    505. 

  505.       <pre>
    506. 

  506. var odds = _.reject([1, 2, 3, 4, 5, 6], function(num){ return num % 2 == 0; });
    507. 

  507. =&gt; [1, 3, 5]
    508. 

  508. </pre>
    509. 

  509. 

  510.       <p id="every">
    511. 

  511.         <b class="header">every</b><code>_.every(list, iterator, [context])</code>
    512. 

  512.         <span class="alias">Alias: <b>all</b></span>
    513. 

  513.         <br />
    514. 

  514.         Returns <i>true</i> if all of the values in the <b>list</b> pass the <b>iterator</b>
    515. 

  515.         truth test. Delegates to the native method <b>every</b>, if present.
    516. 

  516.       </p>
    517. 

  517.       <pre>
    518. 

  518. _.every([true, 1, null, 'yes'], _.identity);
    519. 

  519. =&gt; false
    520. 

  520. </pre>
    521. 

  521. 

  522.       <p id="some">
    523. 

  523.         <b class="header">some</b><code>_.some(list, [iterator], [context])</code>
    524. 

  524.         <span class="alias">Alias: <b>any</b></span>
    525. 

  525.         <br />
    526. 

  526.         Returns <i>true</i> if any of the values in the <b>list</b> pass the
    527. 

  527.         <b>iterator</b> truth test. Short-circuits and stops traversing the list
    528. 

  528.         if a true element is found. Delegates to the native method <b>some</b>,
    529. 

  529.         if present.
    530. 

  530.       </p>
    531. 

  531.       <pre>
    532. 

  532. _.some([null, 0, 'yes', false]);
    533. 

  533. =&gt; true
    534. 

  534. </pre>
    535. 

  535. 

  536.       <p id="contains">
    537. 

  537.         <b class="header">contains</b><code>_.contains(list, value)</code>
    538. 

  538.         <span class="alias">Alias: <b>include</b></span>
    539. 

  539.         <br />
    540. 

  540.         Returns <i>true</i> if the <b>value</b> is present in the <b>list</b>.
    541. 

  541.         Uses <b>indexOf</b> internally, if <b>list</b> is an Array.
    542. 

  542.       </p>
    543. 

  543.       <pre>
    544. 

  544. _.contains([1, 2, 3], 3);
    545. 

  545. =&gt; true
    546. 

  546. </pre>
    547. 

  547. 

  548.       <p id="invoke">
    549. 

  549.         <b class="header">invoke</b><code>_.invoke(list, methodName, [*arguments])</code>
    550. 

  550.         <br />
    551. 

  551.         Calls the method named by <b>methodName</b> on each value in the <b>list</b>.
    552. 

  552.         Any extra arguments passed to <b>invoke</b> will be forwarded on to the
    553. 

  553.         method invocation.
    554. 

  554.       </p>
    555. 

  555.       <pre>
    556. 

  556. _.invoke([[5, 1, 7], [3, 2, 1]], 'sort');
    557. 

  557. =&gt; [[1, 5, 7], [1, 2, 3]]
    558. 

  558. </pre>
    559. 

  559. 

  560.       <p id="pluck">
    561. 

  561.         <b class="header">pluck</b><code>_.pluck(list, propertyName)</code>
    562. 

  562.         <br />
    563. 

  563.         A convenient version of what is perhaps the most common use-case for
    564. 

  564.         <b>map</b>: extracting a list of property values.
    565. 

  565.       </p>
    566. 

  566.       <pre>
    567. 

  567. var stooges = [{name : 'moe', age : 40}, {name : 'larry', age : 50}, {name : 'curly', age : 60}];
    568. 

  568. _.pluck(stooges, 'name');
    569. 

  569. =&gt; ["moe", "larry", "curly"]
    570. 

  570. </pre>
    571. 

  571. 

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

  573.         <b class="header">max</b><code>_.max(list, [iterator], [context])</code>
    574. 

  574.         <br />
    575. 

  575.         Returns the maximum value in <b>list</b>. If <b>iterator</b> is passed,
    576. 

  576.         it will be used on each value to generate the criterion by which the
    577. 

  577.         value is ranked.
    578. 

  578.       </p>
    579. 

  579.       <pre>
    580. 

  580. var stooges = [{name : 'moe', age : 40}, {name : 'larry', age : 50}, {name : 'curly', age : 60}];
    581. 

  581. _.max(stooges, function(stooge){ return stooge.age; });
    582. 

  582. =&gt; {name : 'curly', age : 60};
    583. 

  583. </pre>
    584. 

  584. 

  585.       <p id="min">
    586. 

  586.         <b class="header">min</b><code>_.min(list, [iterator], [context])</code>
    587. 

  587.         <br />
    588. 

  588.         Returns the minimum value in <b>list</b>. If <b>iterator</b> is passed,
    589. 

  589.         it will be used on each value to generate the criterion by which the
    590. 

  590.         value is ranked.
    591. 

  591.       </p>
    592. 

  592.       <pre>
    593. 

  593. var numbers = [10, 5, 100, 2, 1000];
    594. 

  594. _.min(numbers);
    595. 

  595. =&gt; 2
    596. 

  596. </pre>
    597. 

  597. 

  598.       <p id="sortBy">
    599. 

  599.         <b class="header">sortBy</b><code>_.sortBy(list, iterator, [context])</code>
    600. 

  600.         <br />
    601. 

  601.         Returns a sorted copy of <b>list</b>, ranked in ascending order by the
    602. 

  602.         results of running each value through <b>iterator</b>. Iterator may
    603. 

  603.         also be the string name of the property to sort by (eg. <tt>length</tt>).
    604. 

  604.       </p>
    605. 

  605.       <pre>
    606. 

  606. _.sortBy([1, 2, 3, 4, 5, 6], function(num){ return Math.sin(num); });
    607. 

  607. =&gt; [5, 4, 6, 3, 1, 2]
    608. 

  608. </pre>
    609. 

  609. 

  610.       <p id="groupBy">
    611. 

  611.         <b class="header">groupBy</b><code>_.groupBy(list, iterator)</code>
    612. 

  612.         <br />
    613. 

  613.         Splits a collection into sets, grouped by the result of running each
    614. 

  614.         value through <b>iterator</b>. If <b>iterator</b> is a string instead of
    615. 

  615.         a function, groups by the property named by <b>iterator</b> on each of
    616. 

  616.         the values.
    617. 

  617.       </p>
    618. 

  618.       <pre>
    619. 

  619. _.groupBy([1.3, 2.1, 2.4], function(num){ return Math.floor(num); });
    620. 

  620. =&gt; {1: [1.3], 2: [2.1, 2.4]}
    621. 

  621. 

  622. _.groupBy(['one', 'two', 'three'], 'length');
    623. 

  623. =&gt; {3: ["one", "two"], 5: ["three"]}
    624. 

  624. </pre>
    625. 

  625. 

  626.       <p id="countBy">
    627. 

  627.         <b class="header">countBy</b><code>_.countBy(list, iterator)</code>
    628. 

  628.         <br />
    629. 

  629.         Sorts a list into groups and returns a count for the number of objects
    630. 

  630.         in each group.
    631. 

  631.         Similar to <tt>groupBy</tt>, but instead of returning a list of values,
    632. 

  632.         returns a count for the number of values in that group.
    633. 

  633.       </p>
    634. 

  634.       <pre>
    635. 

  635. _.countBy([1, 2, 3, 4, 5], function(num) {
    636. 

  636.   return num % 2 == 0 ? 'even' : 'odd';
    637. 

  637. });
    638. 

  638. =&gt; {odd: 3, even: 2}
    639. 

  639. </pre>
    640. 

  640. 

  641.       <p id="shuffle">
    642. 

  642.         <b class="header">shuffle</b><code>_.shuffle(list)</code>
    643. 

  643.         <br />
    644. 

  644.         Returns a shuffled copy of the <b>list</b>, using a version of the
    645. 

  645.         <a href="http://en.wikipedia.org/wiki/Fisher%E2%80%93Yates_shuffle">Fisher-Yates shuffle</a>.
    646. 

  646.       </p>
    647. 

  647.       <pre>
    648. 

  648. _.shuffle([1, 2, 3, 4, 5, 6]);
    649. 

  649. =&gt; [4, 1, 6, 3, 5, 2]
    650. 

  650. </pre>
    651. 

  651. 

  652.       <p id="toArray">
    653. 

  653.         <b class="header">toArray</b><code>_.toArray(list)</code>
    654. 

  654.         <br />
    655. 

  655.         Converts the <b>list</b> (anything that can be iterated over), into a
    656. 

  656.         real Array. Useful for transmuting the <b>arguments</b> object.
    657. 

  657.       </p>
    658. 

  658.       <pre>
    659. 

  659. (function(){ return _.toArray(arguments).slice(1); })(1, 2, 3, 4);
    660. 

  660. =&gt; [2, 3, 4]
    661. 

  661. </pre>
    662. 

  662. 

  663.       <p id="size">
    664. 

  664.         <b class="header">size</b><code>_.size(list)</code>
    665. 

  665.         <br />
    666. 

  666.         Return the number of values in the <b>list</b>.
    667. 

  667.       </p>
    668. 

  668.       <pre>
    669. 

  669. _.size({one : 1, two : 2, three : 3});
    670. 

  670. =&gt; 3
    671. 

  671. </pre>
    672. 

  672. 

  673.       <h2 id="arrays">Array Functions</h2>
    674. 

  674. 

  675.       <p>
    676. 

  676.         <i>
    677. 

  677.           Note: All array functions will also work on the <b>arguments</b> object.
    678. 

  678.           However, Underscore functions are not designed to work on "sparse" arrays.
    679. 

  679.         </i>
    680. 

  680.       </p>
    681. 

  681. 

  682.       <p id="first">
    683. 

  683.         <b class="header">first</b><code>_.first(array, [n])</code>
    684. 

  684.         <span class="alias">Alias: <b>head</b>, <b>take</b></span>
    685. 

  685.         <br />
    686. 

  686.         Returns the first element of an <b>array</b>. Passing <b>n</b> will
    687. 

  687.         return the first <b>n</b> elements of the array.
    688. 

  688.       </p>
    689. 

  689.       <pre>
    690. 

  690. _.first([5, 4, 3, 2, 1]);
    691. 

  691. =&gt; 5
    692. 

  692. </pre>
    693. 

  693. 

  694.       <p id="initial">
    695. 

  695.         <b class="header">initial</b><code>_.initial(array, [n])</code>
    696. 

  696.         <br />
    697. 

  697.         Returns everything but the last entry of the array. Especially useful on
    698. 

  698.         the arguments object. Pass <b>n</b> to exclude the last <b>n</b> elements
    699. 

  699.         from the result.
    700. 

  700.       </p>
    701. 

  701.       <pre>
    702. 

  702. _.initial([5, 4, 3, 2, 1]);
    703. 

  703. =&gt; [5, 4, 3, 2]
    704. 

  704. </pre>
    705. 

  705. 

  706.       <p id="last">
    707. 

  707.         <b class="header">last</b><code>_.last(array, [n])</code>
    708. 

  708.         <br />
    709. 

  709.         Returns the last element of an <b>array</b>. Passing <b>n</b> will return
    710. 

  710.         the last <b>n</b> elements of the array.
    711. 

  711.       </p>
    712. 

  712.       <pre>
    713. 

  713. _.last([5, 4, 3, 2, 1]);
    714. 

  714. =&gt; 1
    715. 

  715. </pre>
    716. 

  716. 

  717.       <p id="rest">
    718. 

  718.         <b class="header">rest</b><code>_.rest(array, [index])</code>
    719. 

  719.         <span class="alias">Alias: <b>tail, drop</b></span>
    720. 

  720.         <br />
    721. 

  721.         Returns the <b>rest</b> of the elements in an array. Pass an <b>index</b>
    722. 

  722.         to return the values of the array from that index onward.
    723. 

  723.       </p>
    724. 

  724.       <pre>
    725. 

  725. _.rest([5, 4, 3, 2, 1]);
    726. 

  726. =&gt; [4, 3, 2, 1]
    727. 

  727. </pre>
    728. 

  728. 

  729.       <p id="compact">
    730. 

  730.         <b class="header">compact</b><code>_.compact(array)</code>
    731. 

  731.         <br />
    732. 

  732.         Returns a copy of the <b>array</b> with all falsy values removed.
    733. 

  733.         In JavaScript, <i>false</i>, <i>null</i>, <i>0</i>, <i>""</i>,
    734. 

  734.         <i>undefined</i> and <i>NaN</i> are all falsy.
    735. 

  735.       </p>
    736. 

  736.       <pre>
    737. 

  737. _.compact([0, 1, false, 2, '', 3]);
    738. 

  738. =&gt; [1, 2, 3]
    739. 

  739. </pre>
    740. 

  740. 

  741.       <p id="flatten">
    742. 

  742.         <b class="header">flatten</b><code>_.flatten(array, [shallow])</code>
    743. 

  743.         <br />
    744. 

  744.         Flattens a nested <b>array</b> (the nesting can be to any depth). If you
    745. 

  745.         pass <b>shallow</b>, the array will only be flattened a single level.
    746. 

  746.       </p>
    747. 

  747.       <pre>
    748. 

  748. _.flatten([1, [2], [3, [[4]]]]);
    749. 

  749. =&gt; [1, 2, 3, 4];
    750. 

  750. 

  751. _.flatten([1, [2], [3, [[4]]]], true);
    752. 

  752. =&gt; [1, 2, 3, [[4]]];
    753. 

  753. </pre>
    754. 

  754. 

  755.       <p id="without">
    756. 

  756.         <b class="header">without</b><code>_.without(array, [*values])</code>
    757. 

  757.         <br />
    758. 

  758.         Returns a copy of the <b>array</b> with all instances of the <b>values</b>
    759. 

  759.         removed.
    760. 

  760.       </p>
    761. 

  761.       <pre>
    762. 

  762. _.without([1, 2, 1, 0, 3, 1, 4], 0, 1);
    763. 

  763. =&gt; [2, 3, 4]
    764. 

  764. </pre>
    765. 

  765. 

  766.       <p id="union">
    767. 

  767.         <b class="header">union</b><code>_.union(*arrays)</code>
    768. 

  768.         <br />
    769. 

  769.         Computes the union of the passed-in <b>arrays</b>: the list of unique items,
    770. 

  770.         in order, that are present in one or more of the <b>arrays</b>.
    771. 

  771.       </p>
    772. 

  772.       <pre>
    773. 

  773. _.union([1, 2, 3], [101, 2, 1, 10], [2, 1]);
    774. 

  774. =&gt; [1, 2, 3, 101, 10]
    775. 

  775. </pre>
    776. 

  776. 

  777.       <p id="intersection">
    778. 

  778.         <b class="header">intersection</b><code>_.intersection(*arrays)</code>
    779. 

  779.         <br />
    780. 

  780.         Computes the list of values that are the intersection of all the <b>arrays</b>.
    781. 

  781.         Each value in the result is present in each of the <b>arrays</b>.
    782. 

  782.       </p>
    783. 

  783.       <pre>
    784. 

  784. _.intersection([1, 2, 3], [101, 2, 1, 10], [2, 1]);
    785. 

  785. =&gt; [1, 2]
    786. 

  786. </pre>
    787. 

  787. 

  788.       <p id="difference">
    789. 

  789.         <b class="header">difference</b><code>_.difference(array, *others)</code>
    790. 

  790.         <br />
    791. 

  791.         Similar to <b>without</b>, but returns the values from <b>array</b> that
    792. 

  792.         are not present in the <b>other</b> arrays.
    793. 

  793.       </p>
    794. 

  794.       <pre>
    795. 

  795. _.difference([1, 2, 3, 4, 5], [5, 2, 10]);
    796. 

  796. =&gt; [1, 3, 4]
    797. 

  797. </pre>
    798. 

  798. 

  799.       <p id="uniq">
    800. 

  800.         <b class="header">uniq</b><code>_.uniq(array, [isSorted], [iterator])</code>
    801. 

  801.         <span class="alias">Alias: <b>unique</b></span>
    802. 

  802.         <br />
    803. 

  803.         Produces a duplicate-free version of the <b>array</b>, using <i>===</i> to test
    804. 

  804.         object equality. If you know in advance that the <b>array</b> is sorted,
    805. 

  805.         passing <i>true</i> for <b>isSorted</b> will run a much faster algorithm.
    806. 

  806.         If you want to compute unique items based on a transformation, pass an
    807. 

  807.         <b>iterator</b> function.
    808. 

  808.       </p>
    809. 

  809.       <pre>
    810. 

  810. _.uniq([1, 2, 1, 3, 1, 4]);
    811. 

  811. =&gt; [1, 2, 3, 4]
    812. 

  812. </pre>
    813. 

  813. 

  814.       <p id="zip">
    815. 

  815.         <b class="header">zip</b><code>_.zip(*arrays)</code>
    816. 

  816.         <br />
    817. 

  817.         Merges together the values of each of the <b>arrays</b> with the
    818. 

  818.         values at the corresponding position. Useful when you have separate
    819. 

  819.         data sources that are coordinated through matching array indexes.
    820. 

  820.         If you're working with a matrix of nested arrays, <b>zip.apply</b>
    821. 

  821.         can transpose the matrix in a similar fashion.
    822. 

  822.       </p>
    823. 

  823.       <pre>
    824. 

  824. _.zip(['moe', 'larry', 'curly'], [30, 40, 50], [true, false, false]);
    825. 

  825. =&gt; [["moe", 30, true], ["larry", 40, false], ["curly", 50, false]]
    826. 

  826. </pre>
    827. 

  827. 

  828.       <p id="object">
    829. 

  829.         <b class="header">object</b><code>_.object(list, [values])</code>
    830. 

  830.         <br />
    831. 

  831.         Converts arrays into objects. Pass either a single list of
    832. 

  832.         <tt>[key, value]</tt> pairs, or a list of keys, and a list of values.
    833. 

  833.       </p>
    834. 

  834.       <pre>
    835. 

  835. _.object(['moe', 'larry', 'curly'], [30, 40, 50]);
    836. 

  836. =&gt; {moe: 30, larry: 40, curly: 50}
    837. 

  837. 

  838. _.object([['moe', 30], ['larry', 40], ['curly', 50]]);
    839. 

  839. =&gt; {moe: 30, larry: 40, curly: 50}
    840. 

  840. </pre>
    841. 

  841. 

  842.       <p id="indexOf">
    843. 

  843.         <b class="header">indexOf</b><code>_.indexOf(array, value, [isSorted])</code>
    844. 

  844.         <br />
    845. 

  845.         Returns the index at which <b>value</b> can be found in the <b>array</b>,
    846. 

  846.         or <i>-1</i> if value is not present in the <b>array</b>. Uses the native
    847. 

  847.         <b>indexOf</b> function unless it's missing. If you're working with a
    848. 

  848.         large array, and you know that the array is already sorted, pass <tt>true</tt>
    849. 

  849.         for <b>isSorted</b> to use a faster binary search ... or, pass a number as
    850. 

  850.         the third argument in order to look for the first matching value in the
    851. 

  851.         array after the given index.
    852. 

  852.       </p>
    853. 

  853.       <pre>
    854. 

  854. _.indexOf([1, 2, 3], 2);
    855. 

  855. =&gt; 1
    856. 

  856. </pre>
    857. 

  857. 

  858.       <p id="lastIndexOf">
    859. 

  859.         <b class="header">lastIndexOf</b><code>_.lastIndexOf(array, value, [fromIndex])</code>
    860. 

  860.         <br />
    861. 

  861.         Returns the index of the last occurrence of <b>value</b> in the <b>array</b>,
    862. 

  862.         or <i>-1</i> if value is not present. Uses the native <b>lastIndexOf</b>
    863. 

  863.         function if possible. Pass <b>fromIndex</b> to start your search at a
    864. 

  864.         given index.
    865. 

  865.       </p>
    866. 

  866.       <pre>
    867. 

  867. _.lastIndexOf([1, 2, 3, 1, 2, 3], 2);
    868. 

  868. =&gt; 4
    869. 

  869. </pre>
    870. 

  870. 

  871.       <p id="sortedIndex">
    872. 

  872.         <b class="header">sortedIndex</b><code>_.sortedIndex(list, value, [iterator])</code>
    873. 

  873.         <br />
    874. 

  874.         Uses a binary search to determine the index at which the <b>value</b>
    875. 

  875.         <i>should</i> be inserted into the <b>list</b> in order to maintain the <b>list</b>'s
    876. 

  876.         sorted order. If an <b>iterator</b> is passed, it will be used to compute
    877. 

  877.         the sort ranking of each value, including the <b>value</b> you pass.
    878. 

  878.       </p>
    879. 

  879.       <pre>
    880. 

  880. _.sortedIndex([10, 20, 30, 40, 50], 35);
    881. 

  881. =&gt; 3
    882. 

  882. </pre>
    883. 

  883. 

  884.       <p id="range">
    885. 

  885.         <b class="header">range</b><code>_.range([start], stop, [step])</code>
    886. 

  886.         <br />
    887. 

  887.         A function to create flexibly-numbered lists of integers, handy for
    888. 

  888.         <tt>each</tt> and <tt>map</tt> loops. <b>start</b>, if omitted, defaults
    889. 

  889.         to <i>0</i>; <b>step</b> defaults to <i>1</i>. Returns a list of integers
    890. 

  890.         from <b>start</b> to <b>stop</b>, incremented (or decremented) by <b>step</b>,
    891. 

  891.         exclusive.
    892. 

  892.       </p>
    893. 

  893.       <pre>
    894. 

  894. _.range(10);
    895. 

  895. =&gt; [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
    896. 

  896. _.range(1, 11);
    897. 

  897. =&gt; [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
    898. 

  898. _.range(0, 30, 5);
    899. 

  899. =&gt; [0, 5, 10, 15, 20, 25]
    900. 

  900. _.range(0, -10, -1);
    901. 

  901. =&gt; [0, -1, -2, -3, -4, -5, -6, -7, -8, -9]
    902. 

  902. _.range(0);
    903. 

  903. =&gt; []
    904. 

  904. </pre>
    905. 

  905. 

  906.       <h2 id="functions">Function (uh, ahem) Functions</h2>
    907. 

  907. 

  908.       <p id="bind">
    909. 

  909.         <b class="header">bind</b><code>_.bind(function, object, [*arguments])</code>
    910. 

  910.         <br />
    911. 

  911.         Bind a <b>function</b> to an <b>object</b>, meaning that whenever
    912. 

  912.         the function is called, the value of <i>this</i> will be the <b>object</b>.
    913. 

  913.         Optionally, bind <b>arguments</b> to the <b>function</b> to pre-fill them,
    914. 

  914.         also known as <b>partial application</b>.
    915. 

  915.       </p>
    916. 

  916.       <pre>
    917. 

  917. var func = function(greeting){ return greeting + ': ' + this.name };
    918. 

  918. func = _.bind(func, {name : 'moe'}, 'hi');
    919. 

  919. func();
    920. 

  920. =&gt; 'hi: moe'
    921. 

  921. </pre>
    922. 

  922. 

  923.       <p id="bindAll">
    924. 

  924.         <b class="header">bindAll</b><code>_.bindAll(object, [*methodNames])</code>
    925. 

  925.         <br />
    926. 

  926.         Binds a number of methods on the <b>object</b>, specified by
    927. 

  927.         <b>methodNames</b>, to be run in the context of that object whenever they
    928. 

  928.         are invoked. Very handy for binding functions that are going to be used
    929. 

  929.         as event handlers, which would otherwise be invoked with a fairly useless
    930. 

  930.         <i>this</i>. If no <b>methodNames</b> are provided, all of the object's
    931. 

  931.         function properties will be bound to it.
    932. 

  932.       </p>
    933. 

  933.       <pre>
    934. 

  934. var buttonView = {
    935. 

  935.   label   : 'underscore',
    936. 

  936.   onClick : function(){ alert('clicked: ' + this.label); },
    937. 

  937.   onHover : function(){ console.log('hovering: ' + this.label); }
    938. 

  938. };
    939. 

  939. _.bindAll(buttonView);
    940. 

  940. jQuery('#underscore_button').bind('click', buttonView.onClick);
    941. 

  941. =&gt; When the button is clicked, this.label will have the correct value...
    942. 

  942. </pre>
    943. 

  943. 

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

  945.         <b class="header">memoize</b><code>_.memoize(function, [hashFunction])</code>
    946. 

  946.         <br />
    947. 

  947.         Memoizes a given <b>function</b> by caching the computed result. Useful
    948. 

  948.         for speeding up slow-running computations. If passed an optional
    949. 

  949.         <b>hashFunction</b>, it will be used to compute the hash key for storing
    950. 

  950.         the result, based on the arguments to the original function. The default
    951. 

  951.         <b>hashFunction</b> just uses the first argument to the memoized function
    952. 

  952.         as the key.
    953. 

  953.       </p>
    954. 

  954.       <pre>
    955. 

  955. var fibonacci = _.memoize(function(n) {
    956. 

  956.   return n &lt; 2 ? n : fibonacci(n - 1) + fibonacci(n - 2);
    957. 

  957. });
    958. 

  958. </pre>
    959. 

  959. 

  960.       <p id="delay">
    961. 

  961.         <b class="header">delay</b><code>_.delay(function, wait, [*arguments])</code>
    962. 

  962.         <br />
    963. 

  963.         Much like <b>setTimeout</b>, invokes <b>function</b> after <b>wait</b>
    964. 

  964.         milliseconds. If you pass the optional <b>arguments</b>, they will be
    965. 

  965.         forwarded on to the <b>function</b> when it is invoked.
    966. 

  966.       </p>
    967. 

  967.       <pre>
    968. 

  968. var log = _.bind(console.log, console);
    969. 

  969. _.delay(log, 1000, 'logged later');
    970. 

  970. =&gt; 'logged later' // Appears after one second.
    971. 

  971. </pre>
    972. 

  972. 

  973.       <p id="defer">
    974. 

  974.         <b class="header">defer</b><code>_.defer(function, [*arguments])</code>
    975. 

  975.         <br />
    976. 

  976.         Defers invoking the <b>function</b> until the current call stack has cleared,
    977. 

  977.         similar to using <b>setTimeout</b> with a delay of 0. Useful for performing
    978. 

  978.         expensive computations or HTML rendering in chunks without blocking the UI thread
    979. 

  979.         from updating. If you pass the optional <b>arguments</b>, they will be
    980. 

  980.         forwarded on to the <b>function</b> when it is invoked.
    981. 

  981.       </p>
    982. 

  982.       <pre>
    983. 

  983. _.defer(function(){ alert('deferred'); });
    984. 

  984. // Returns from the function before the alert runs.
    985. 

  985. </pre>
    986. 

  986. 

  987.       <p id="throttle">
    988. 

  988.         <b class="header">throttle</b><code>_.throttle(function, wait)</code>
    989. 

  989.         <br />
    990. 

  990.         Creates and returns a new, throttled version of the passed function,
    991. 

  991.         that, when invoked repeatedly, will only actually call the original function
    992. 

  992.         at most once per every <b>wait</b>
    993. 

  993.         milliseconds. Useful for rate-limiting events that occur faster than you
    994. 

  994.         can keep up with.
    995. 

  995.       </p>
    996. 

  996.       <pre>
    997. 

  997. var throttled = _.throttle(updatePosition, 100);
    998. 

  998. $(window).scroll(throttled);
    999. 

  999. </pre>
    1000. 

  1000. 

  1001.       <p id="debounce">
    1002. 

  1002.         <b class="header">debounce</b><code>_.debounce(function, wait, [immediate])</code>
    1003. 

  1003.         <br />
    1004. 

  1004.         Creates and returns a new debounced version of the passed function that
    1005. 

  1005.         will postpone its execution until after
    1006. 

  1006.         <b>wait</b> milliseconds have elapsed since the last time it
    1007. 

  1007.         was invoked. Useful for implementing behavior that should only happen
    1008. 

  1008.         <i>after</i> the input has stopped arriving. For example: rendering a
    1009. 

  1009.         preview of a Markdown comment, recalculating a layout after the window
    1010. 

  1010.         has stopped being resized, and so on.
    1011. 

  1011.       </p>
    1012. 

  1012. 

  1013.       <p>
    1014. 

  1014.         Pass <tt>true</tt> for the <b>immediate</b> parameter to cause
    1015. 

  1015.         <b>debounce</b> to trigger the function on the leading instead of the
    1016. 

  1016.         trailing edge of the <b>wait</b> interval. Useful in circumstances like
    1017. 

  1017.         preventing accidental double-clicks on a "submit" button from firing a
    1018. 

  1018.         second time.
    1019. 

  1019.       </p>
    1020. 

  1020. 

  1021.       <pre>
    1022. 

  1022. var lazyLayout = _.debounce(calculateLayout, 300);
    1023. 

  1023. $(window).resize(lazyLayout);
    1024. 

  1024. </pre>
    1025. 

  1025. 

  1026.       <p id="once">
    1027. 

  1027.         <b class="header">once</b><code>_.once(function)</code>
    1028. 

  1028.         <br />
    1029. 

  1029.         Creates a version of the function that can only be called one time.
    1030. 

  1030.         Repeated calls to the modified function will have no effect, returning
    1031. 

  1031.         the value from the original call. Useful for initialization functions,
    1032. 

  1032.         instead of having to set a boolean flag and then check it later.
    1033. 

  1033.       </p>
    1034. 

  1034.       <pre>
    1035. 

  1035. var initialize = _.once(createApplication);
    1036. 

  1036. initialize();
    1037. 

  1037. initialize();
    1038. 

  1038. // Application is only created once.
    1039. 

  1039. </pre>
    1040. 

  1040. 

  1041.       <p id="after">
    1042. 

  1042.         <b class="header">after</b><code>_.after(count, function)</code>
    1043. 

  1043.         <br />
    1044. 

  1044.         Creates a version of the function that will only be run after first
    1045. 

  1045.         being called <b>count</b> times. Useful for grouping asynchronous responses,
    1046. 

  1046.         where you want to be sure that all the async calls have finished, before
    1047. 

  1047.         proceeding.
    1048. 

  1048.       </p>
    1049. 

  1049.       <pre>
    1050. 

  1050. var renderNotes = _.after(notes.length, render);
    1051. 

  1051. _.each(notes, function(note) {
    1052. 

  1052.   note.asyncSave({success: renderNotes});
    1053. 

  1053. });
    1054. 

  1054. // renderNotes is run once, after all notes have saved.
    1055. 

  1055. </pre>
    1056. 

  1056. 

  1057.       <p id="wrap">
    1058. 

  1058.         <b class="header">wrap</b><code>_.wrap(function, wrapper)</code>
    1059. 

  1059.         <br />
    1060. 

  1060.         Wraps the first <b>function</b> inside of the <b>wrapper</b> function,
    1061. 

  1061.         passing it as the first argument. This allows the <b>wrapper</b> to
    1062. 

  1062.         execute code before and after the <b>function</b> runs, adjust the arguments,
    1063. 

  1063.         and execute it conditionally.
    1064. 

  1064.       </p>
    1065. 

  1065.       <pre>
    1066. 

  1066. var hello = function(name) { return "hello: " + name; };
    1067. 

  1067. hello = _.wrap(hello, function(func) {
    1068. 

  1068.   return "before, " + func("moe") + ", after";
    1069. 

  1069. });
    1070. 

  1070. hello();
    1071. 

  1071. =&gt; 'before, hello: moe, after'
    1072. 

  1072. </pre>
    1073. 

  1073. 

  1074.       <p id="compose">
    1075. 

  1075.         <b class="header">compose</b><code>_.compose(*functions)</code>
    1076. 

  1076.         <br />
    1077. 

  1077.         Returns the composition of a list of <b>functions</b>, where each function
    1078. 

  1078.         consumes the return value of the function that follows. In math terms,
    1079. 

  1079.         composing the functions <i>f()</i>, <i>g()</i>, and <i>h()</i> produces
    1080. 

  1080.         <i>f(g(h()))</i>.
    1081. 

  1081.       </p>
    1082. 

  1082.       <pre>
    1083. 

  1083. var greet    = function(name){ return "hi: " + name; };
    1084. 

  1084. var exclaim  = function(statement){ return statement + "!"; };
    1085. 

  1085. var welcome = _.compose(exclaim, greet);
    1086. 

  1086. welcome('moe');
    1087. 

  1087. =&gt; 'hi: moe!'
    1088. 

  1088. </pre>
    1089. 

  1089. 

  1090.       <h2 id="objects">Object Functions</h2>
    1091. 

  1091. 

  1092.       <p id="keys">
    1093. 

  1093.         <b class="header">keys</b><code>_.keys(object)</code>
    1094. 

  1094.         <br />
    1095. 

  1095.         Retrieve all the names of the <b>object</b>'s properties.
    1096. 

  1096.       </p>
    1097. 

  1097.       <pre>
    1098. 

  1098. _.keys({one : 1, two : 2, three : 3});
    1099. 

  1099. =&gt; ["one", "two", "three"]
    1100. 

  1100. </pre>
    1101. 

  1101. 

  1102.       <p id="values">
    1103. 

  1103.         <b class="header">values</b><code>_.values(object)</code>
    1104. 

  1104.         <br />
    1105. 

  1105.         Return all of the values of the <b>object</b>'s properties.
    1106. 

  1106.       </p>
    1107. 

  1107.       <pre>
    1108. 

  1108. _.values({one : 1, two : 2, three : 3});
    1109. 

  1109. =&gt; [1, 2, 3]
    1110. 

  1110. </pre>
    1111. 

  1111. 

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

  1113.         <b class="header">pairs</b><code>_.pairs(object)</code>
    1114. 

  1114.         <br />
    1115. 

  1115.         Convert an object into a list of <tt>[key, value]</tt> pairs.
    1116. 

  1116.       </p>
    1117. 

  1117.       <pre>
    1118. 

  1118. _.pairs({one: 1, two: 2, three: 3});
    1119. 

  1119. =&gt; [["one", 1], ["two", 2], ["three", 3]]
    1120. 

  1120. </pre>
    1121. 

  1121. 

  1122.       <p id="invert">
    1123. 

  1123.         <b class="header">invert</b><code>_.invert(object)</code>
    1124. 

  1124.         <br />
    1125. 

  1125.         Returns a copy of the <b>object</b> where the keys have become the values
    1126. 

  1126.         and the values the keys. For this to work, all of your object's values
    1127. 

  1127.         should be unique and string serializable.
    1128. 

  1128.       </p>
    1129. 

  1129.       <pre>
    1130. 

  1130. _.invert({Moe: "Moses", Larry: "Louis", Curly: "Jerome"});
    1131. 

  1131. =&gt; {Moses: "Moe", Louis: "Larry", Jerome: "Curly"};
    1132. 

  1132. </pre>
    1133. 

  1133. 

  1134.       <p id="object-functions">
    1135. 

  1135.         <b class="header">functions</b><code>_.functions(object)</code>
    1136. 

  1136.         <span class="alias">Alias: <b>methods</b></span>
    1137. 

  1137.         <br />
    1138. 

  1138.         Returns a sorted list of the names of every method in an object &mdash;
    1139. 

  1139.         that is to say, the name of every function property of the object.
    1140. 

  1140.       </p>
    1141. 

  1141.       <pre>
    1142. 

  1142. _.functions(_);
    1143. 

  1143. =&gt; ["all", "any", "bind", "bindAll", "clone", "compact", "compose" ...
    1144. 

  1144. </pre>
    1145. 

  1145. 

  1146.       <p id="extend">
    1147. 

  1147.         <b class="header">extend</b><code>_.extend(destination, *sources)</code>
    1148. 

  1148.         <br />
    1149. 

  1149.         Copy all of the properties in the <b>source</b> objects over to the
    1150. 

  1150.         <b>destination</b> object, and return the <b>destination</b> object.
    1151. 

  1151.         It's in-order, so the last source will override properties of the same
    1152. 

  1152.         name in previous arguments.
    1153. 

  1153.       </p>
    1154. 

  1154.       <pre>
    1155. 

  1155. _.extend({name : 'moe'}, {age : 50});
    1156. 

  1156. =&gt; {name : 'moe', age : 50}
    1157. 

  1157. </pre>
    1158. 

  1158. 

  1159.       <p id="pick">
    1160. 

  1160.         <b class="header">pick</b><code>_.pick(object, *keys)</code>
    1161. 

  1161.         <br />
    1162. 

  1162.         Return a copy of the <b>object</b>, filtered to only have values for
    1163. 

  1163.         the whitelisted <b>keys</b> (or array of valid keys).
    1164. 

  1164.       </p>
    1165. 

  1165.       <pre>
    1166. 

  1166. _.pick({name : 'moe', age: 50, userid : 'moe1'}, 'name', 'age');
    1167. 

  1167. =&gt; {name : 'moe', age : 50}
    1168. 

  1168. </pre>
    1169. 

  1169. 

  1170.       <p id="omit">
    1171. 

  1171.         <b class="header">omit</b><code>_.omit(object, *keys)</code>
    1172. 

  1172.         <br />
    1173. 

  1173.         Return a copy of the <b>object</b>, filtered to omit the blacklisted
    1174. 

  1174.         <b>keys</b> (or array of keys).
    1175. 

  1175.       </p>
    1176. 

  1176.       <pre>
    1177. 

  1177. _.omit({name : 'moe', age : 50, userid : 'moe1'}, 'userid');
    1178. 

  1178. =&gt; {name : 'moe', age : 50}
    1179. 

  1179. </pre>
    1180. 

  1180. 

  1181.       <p id="defaults">
    1182. 

  1182.         <b class="header">defaults</b><code>_.defaults(object, *defaults)</code>
    1183. 

  1183.         <br />
    1184. 

  1184.         Fill in null and undefined properties in <b>object</b> with values from the
    1185. 

  1185.         <b>defaults</b> objects, and return the <b>object</b>. As soon as the
    1186. 

  1186.         property is filled, further defaults will have no effect.
    1187. 

  1187.       </p>
    1188. 

  1188.       <pre>
    1189. 

  1189. var iceCream = {flavor : "chocolate"};
    1190. 

  1190. _.defaults(iceCream, {flavor : "vanilla", sprinkles : "lots"});
    1191. 

  1191. =&gt; {flavor : "chocolate", sprinkles : "lots"}
    1192. 

  1192. </pre>
    1193. 

  1193. 

  1194.       <p id="clone">
    1195. 

  1195.         <b class="header">clone</b><code>_.clone(object)</code>
    1196. 

  1196.         <br />
    1197. 

  1197.         Create a shallow-copied clone of the <b>object</b>. Any nested objects
    1198. 

  1198.         or arrays will be copied by reference, not duplicated.
    1199. 

  1199.       </p>
    1200. 

  1200.       <pre>
    1201. 

  1201. _.clone({name : 'moe'});
    1202. 

  1202. =&gt; {name : 'moe'};
    1203. 

  1203. </pre>
    1204. 

  1204. 

  1205.       <p id="tap">
    1206. 

  1206.         <b class="header">tap</b><code>_.tap(object, interceptor)</code>
    1207. 

  1207.         <br />
    1208. 

  1208.         Invokes <b>interceptor</b> with the <b>object</b>, and then returns <b>object</b>.
    1209. 

  1209.         The primary purpose of this method is to "tap into" a method chain, in order to perform operations on intermediate results within the chain.
    1210. 

  1210.       </p>
    1211. 

  1211.       <pre>
    1212. 

  1212. _.chain([1,2,3,200])
    1213. 

  1213.   .filter(function(num) { return num % 2 == 0; })
    1214. 

  1214.   .tap(alert)
    1215. 

  1215.   .map(function(num) { return num * num })
    1216. 

  1216.   .value();
    1217. 

  1217. =&gt; // [2, 200] (alerted)
    1218. 

  1218. =&gt; [4, 40000]
    1219. 

  1219. </pre>
    1220. 

  1220. 

  1221.       <p id="has">
    1222. 

  1222.         <b class="header">has</b><code>_.has(object, key)</code>
    1223. 

  1223.         <br />
    1224. 

  1224.         Does the object contain the given key? Identical to
    1225. 

  1225.         <tt>object.hasOwnProperty(key)</tt>, but uses a safe reference to the
    1226. 

  1226.         <tt>hasOwnProperty</tt> function, in case it's been
    1227. 

  1227.         <a href="http://www.devthought.com/2012/01/18/an-object-is-not-a-hash/">overridden accidentally</a>.
    1228. 

  1228.       </p>
    1229. 

  1229.       <pre>
    1230. 

  1230. _.has({a: 1, b: 2, c: 3}, "b");
    1231. 

  1231. =&gt; true
    1232. 

  1232. </pre>
    1233. 

  1233. 

  1234.       <p id="isEqual">
    1235. 

  1235.         <b class="header">isEqual</b><code>_.isEqual(object, other)</code>
    1236. 

  1236.         <br />
    1237. 

  1237.         Performs an optimized deep comparison between the two objects, to determine
    1238. 

  1238.         if they should be considered equal.
    1239. 

  1239.       </p>
    1240. 

  1240.       <pre>
    1241. 

  1241. var moe   = {name : 'moe', luckyNumbers : [13, 27, 34]};
    1242. 

  1242. var clone = {name : 'moe', luckyNumbers : [13, 27, 34]};
    1243. 

  1243. moe == clone;
    1244. 

  1244. =&gt; false
    1245. 

  1245. _.isEqual(moe, clone);
    1246. 

  1246. =&gt; true
    1247. 

  1247. </pre>
    1248. 

  1248. 

  1249.       <p id="isEmpty">
    1250. 

  1250.         <b class="header">isEmpty</b><code>_.isEmpty(object)</code>
    1251. 

  1251.         <br />
    1252. 

  1252.         Returns <i>true</i> if <b>object</b> contains no values.
    1253. 

  1253.       </p>
    1254. 

  1254.       <pre>
    1255. 

  1255. _.isEmpty([1, 2, 3]);
    1256. 

  1256. =&gt; false
    1257. 

  1257. _.isEmpty({});
    1258. 

  1258. =&gt; true
    1259. 

  1259. </pre>
    1260. 

  1260. 

  1261.       <p id="isElement">
    1262. 

  1262.         <b class="header">isElement</b><code>_.isElement(object)</code>
    1263. 

  1263.         <br />
    1264. 

  1264.         Returns <i>true</i> if <b>object</b> is a DOM element.
    1265. 

  1265.       </p>
    1266. 

  1266.       <pre>
    1267. 

  1267. _.isElement(jQuery('body')[0]);
    1268. 

  1268. =&gt; true
    1269. 

  1269. </pre>
    1270. 

  1270. 

  1271.       <p id="isArray">
    1272. 

  1272.         <b class="header">isArray</b><code>_.isArray(object)</code>
    1273. 

  1273.         <br />
    1274. 

  1274.         Returns <i>true</i> if <b>object</b> is an Array.
    1275. 

  1275.       </p>
    1276. 

  1276.       <pre>
    1277. 

  1277. (function(){ return _.isArray(arguments); })();
    1278. 

  1278. =&gt; false
    1279. 

  1279. _.isArray([1,2,3]);
    1280. 

  1280. =&gt; true
    1281. 

  1281. </pre>
    1282. 

  1282. 

  1283.       <p id="isObject">
    1284. 

  1284.         <b class="header">isObject</b><code>_.isObject(value)</code>
    1285. 

  1285.         <br />
    1286. 

  1286.         Returns <i>true</i> if <b>value</b> is an Object. Note that JavaScript
    1287. 

  1287.         arrays and functions are objects, while (normal) strings and numbers are not.
    1288. 

  1288.       </p>
    1289. 

  1289.       <pre>
    1290. 

  1290. _.isObject({});
    1291. 

  1291. =&gt; true
    1292. 

  1292. _.isObject(1);
    1293. 

  1293. =&gt; false
    1294. 

  1294. </pre>
    1295. 

  1295. 

  1296.       <p id="isArguments">
    1297. 

  1297.         <b class="header">isArguments</b><code>_.isArguments(object)</code>
    1298. 

  1298.         <br />
    1299. 

  1299.         Returns <i>true</i> if <b>object</b> is an Arguments object.
    1300. 

  1300.       </p>
    1301. 

  1301.       <pre>
    1302. 

  1302. (function(){ return _.isArguments(arguments); })(1, 2, 3);
    1303. 

  1303. =&gt; true
    1304. 

  1304. _.isArguments([1,2,3]);
    1305. 

  1305. =&gt; false
    1306. 

  1306. </pre>
    1307. 

  1307. 

  1308.       <p id="isFunction">
    1309. 

  1309.         <b class="header">isFunction</b><code>_.isFunction(object)</code>
    1310. 

  1310.         <br />
    1311. 

  1311.         Returns <i>true</i> if <b>object</b> is a Function.
    1312. 

  1312.       </p>
    1313. 

  1313.       <pre>
    1314. 

  1314. _.isFunction(alert);
    1315. 

  1315. =&gt; true
    1316. 

  1316. </pre>
    1317. 

  1317. 

  1318.       <p id="isString">
    1319. 

  1319.         <b class="header">isString</b><code>_.isString(object)</code>
    1320. 

  1320.         <br />
    1321. 

  1321.         Returns <i>true</i> if <b>object</b> is a String.
    1322. 

  1322.       </p>
    1323. 

  1323.       <pre>
    1324. 

  1324. _.isString("moe");
    1325. 

  1325. =&gt; true
    1326. 

  1326. </pre>
    1327. 

  1327. 

  1328.       <p id="isNumber">
    1329. 

  1329.         <b class="header">isNumber</b><code>_.isNumber(object)</code>
    1330. 

  1330.         <br />
    1331. 

  1331.         Returns <i>true</i> if <b>object</b> is a Number (including <tt>NaN</tt>).
    1332. 

  1332.       </p>
    1333. 

  1333.       <pre>
    1334. 

  1334. _.isNumber(8.4 * 5);
    1335. 

  1335. =&gt; true
    1336. 

  1336. </pre>
    1337. 

  1337. 

  1338.       <p id="isFinite">
    1339. 

  1339.         <b class="header">isFinite</b><code>_.isFinite(object)</code>
    1340. 

  1340.         <br />
    1341. 

  1341.         Returns <i>true</i> if <b>object</b> is a finite Number.
    1342. 

  1342.       </p>
    1343. 

  1343.       <pre>
    1344. 

  1344. _.isFinite(-101);
    1345. 

  1345. =&gt; true
    1346. 

  1346. 

  1347. _.isFinite(-Infinity);
    1348. 

  1348. =&gt; false
    1349. 

  1349. </pre>
    1350. 

  1350. 

  1351.       <p id="isBoolean">
    1352. 

  1352.         <b class="header">isBoolean</b><code>_.isBoolean(object)</code>
    1353. 

  1353.         <br />
    1354. 

  1354.         Returns <i>true</i> if <b>object</b> is either <i>true</i> or <i>false</i>.
    1355. 

  1355.       </p>
    1356. 

  1356.       <pre>
    1357. 

  1357. _.isBoolean(null);
    1358. 

  1358. =&gt; false
    1359. 

  1359. </pre>
    1360. 

  1360. 

  1361.       <p id="isDate">
    1362. 

  1362.         <b class="header">isDate</b><code>_.isDate(object)</code>
    1363. 

  1363.         <br />
    1364. 

  1364.         Returns <i>true</i> if <b>object</b> is a Date.
    1365. 

  1365.       </p>
    1366. 

  1366.       <pre>
    1367. 

  1367. _.isDate(new Date());
    1368. 

  1368. =&gt; true
    1369. 

  1369. </pre>
    1370. 

  1370. 

  1371.       <p id="isRegExp">
    1372. 

  1372.         <b class="header">isRegExp</b><code>_.isRegExp(object)</code>
    1373. 

  1373.         <br />
    1374. 

  1374.         Returns <i>true</i> if <b>object</b> is a RegExp.
    1375. 

  1375.       </p>
    1376. 

  1376.       <pre>
    1377. 

  1377. _.isRegExp(/moe/);
    1378. 

  1378. =&gt; true
    1379. 

  1379. </pre>
    1380. 

  1380. 

  1381.       <p id="isNaN">
    1382. 

  1382.         <b class="header">isNaN</b><code>_.isNaN(object)</code>
    1383. 

  1383.         <br />
    1384. 

  1384.         Returns <i>true</i> if <b>object</b> is <i>NaN</i>.<br /> Note: this is not
    1385. 

  1385.         the same as the native <b>isNaN</b> function, which will also return
    1386. 

  1386.         true if the variable is <i>undefined</i>.
    1387. 

  1387.       </p>
    1388. 

  1388.       <pre>
    1389. 

  1389. _.isNaN(NaN);
    1390. 

  1390. =&gt; true
    1391. 

  1391. isNaN(undefined);
    1392. 

  1392. =&gt; true
    1393. 

  1393. _.isNaN(undefined);
    1394. 

  1394. =&gt; false
    1395. 

  1395. </pre>
    1396. 

  1396. 

  1397.       <p id="isNull">
    1398. 

  1398.         <b class="header">isNull</b><code>_.isNull(object)</code>
    1399. 

  1399.         <br />
    1400. 

  1400.         Returns <i>true</i> if the value of <b>object</b> is <i>null</i>.
    1401. 

  1401.       </p>
    1402. 

  1402.       <pre>
    1403. 

  1403. _.isNull(null);
    1404. 

  1404. =&gt; true
    1405. 

  1405. _.isNull(undefined);
    1406. 

  1406. =&gt; false
    1407. 

  1407. </pre>
    1408. 

  1408. 

  1409.       <p id="isUndefined">
    1410. 

  1410.         <b class="header">isUndefined</b><code>_.isUndefined(value)</code>
    1411. 

  1411.         <br />
    1412. 

  1412.         Returns <i>true</i> if <b>value</b> is <i>undefined</i>.
    1413. 

  1413.       </p>
    1414. 

  1414.       <pre>
    1415. 

  1415. _.isUndefined(window.missingVariable);
    1416. 

  1416. =&gt; true
    1417. 

  1417. </pre>
    1418. 

  1418. 

  1419.       <h2 id="utility">Utility Functions</h2>
    1420. 

  1420. 

  1421.       <p id="noConflict">
    1422. 

  1422.         <b class="header">noConflict</b><code>_.noConflict()</code>
    1423. 

  1423.         <br />
    1424. 

  1424.         Give control of the "_" variable back to its previous owner. Returns
    1425. 

  1425.         a reference to the <b>Underscore</b> object.
    1426. 

  1426.       </p>
    1427. 

  1427.       <pre>
    1428. 

  1428. var underscore = _.noConflict();</pre>
    1429. 

  1429. 

  1430.       <p id="identity">
    1431. 

  1431.         <b class="header">identity</b><code>_.identity(value)</code>
    1432. 

  1432.         <br />
    1433. 

  1433.         Returns the same value that is used as the argument. In math:
    1434. 

  1434.         <tt>f(x) = x</tt><br />
    1435. 

  1435.         This function looks useless, but is used throughout Underscore as
    1436. 

  1436.         a default iterator.
    1437. 

  1437.       </p>
    1438. 

  1438.       <pre>
    1439. 

  1439. var moe = {name : 'moe'};
    1440. 

  1440. moe === _.identity(moe);
    1441. 

  1441. =&gt; true</pre>
    1442. 

  1442. 

  1443.       <p id="times">
    1444. 

  1444.         <b class="header">times</b><code>_.times(n, iterator, [context])</code>
    1445. 

  1445.         <br />
    1446. 

  1446.         Invokes the given iterator function <b>n</b> times. Each invocation of
    1447. 

  1447.         <b>iterator</b> is called with an <tt>index</tt> argument.
    1448. 

  1448.         <br />
    1449. 

  1449.         <i>Note: this example uses the <a href="#chaining">chaining syntax</a></i>.
    1450. 

  1450.       </p>
    1451. 

  1451.       <pre>
    1452. 

  1452. _(3).times(function(n){ genie.grantWishNumber(n); });</pre>
    1453. 

  1453. 

  1454.       <p id="random">
    1455. 

  1455.         <b class="header">random</b><code>_.random(min, max)</code>
    1456. 

  1456.         <br />
    1457. 

  1457.         Returns a random integer between <b>min</b> and <b>max</b>, inclusive.
    1458. 

  1458.         If you only pass one argument, it will return a number between <tt>0</tt>
    1459. 

  1459.         and that number.
    1460. 

  1460.       </p>
    1461. 

  1461.       <pre>
    1462. 

  1462. _.random(0, 100);
    1463. 

  1463. =&gt; 42</pre>
    1464. 

  1464. 

  1465.       <p id="mixin">
    1466. 

  1466.         <b class="header">mixin</b><code>_.mixin(object)</code>
    1467. 

  1467.         <br />
    1468. 

  1468.         Allows you to extend Underscore with your own utility functions. Pass
    1469. 

  1469.         a hash of <tt>{name: function}</tt> definitions to have your functions
    1470. 

  1470.         added to the Underscore object, as well as the OOP wrapper.
    1471. 

  1471.       </p>
    1472. 

  1472.       <pre>
    1473. 

  1473. _.mixin({
    1474. 

  1474.   capitalize : function(string) {
    1475. 

  1475.     return string.charAt(0).toUpperCase() + string.substring(1).toLowerCase();
    1476. 

  1476.   }
    1477. 

  1477. });
    1478. 

  1478. _("fabio").capitalize();
    1479. 

  1479. =&gt; "Fabio"
    1480. 

  1480. </pre>
    1481. 

  1481. 

  1482.       <p id="uniqueId">
    1483. 

  1483.         <b class="header">uniqueId</b><code>_.uniqueId([prefix])</code>
    1484. 

  1484.         <br />
    1485. 

  1485.         Generate a globally-unique id for client-side models or DOM elements
    1486. 

  1486.         that need one. If <b>prefix</b> is passed, the id will be appended to it.
    1487. 

  1487.         Without <b>prefix</b>, returns an integer.
    1488. 

  1488.       </…
    1489.

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