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    164. 

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    167. 

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    168. 

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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">(1.4.0)</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="#all">all</a></li>
    202. 

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

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

  303.     </ul>
    304. 

  304. 

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

  306.       Chaining
    307. 

  307.     </a>
    308. 

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

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

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

  311.     </ul>
    312. 

  312. 

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

  314.       Links
    315. 

  315.     </a>
    316. 

  316. 

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

  318.       Change Log
    319. 

  319.     </a>
    320. 

  320. 

  321.   </div>
    322. 

  322. 

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

  324. 

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

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

  327.     </p>
    328. 

  328. 

  329.     <p>
    330. 

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

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

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

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

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

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

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

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

  338.     </p>
    339. 

  339. 

  340.     <p>
    341. 

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

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

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

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

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

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

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

  348.     </p>
    349. 

  349. 

  350.     <p>
    351. 

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

  352.       is included for your perusal.
    353. 

  353.     </p>
    354. 

  354. 

  355.     <p>
    356. 

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

  357.     </p>
    358. 

  358. 

  359.     <p>
    360. 

  360.       The project is
    361. 

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

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

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

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

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

  366.     </p>
    367. 

  367. 

  368.     <p>
    369. 

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

  370.     </p>
    371. 

  371. 

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

  373. 

  374.     <table>
    375. 

  375.       <tr>
    376. 

  376.         <td><a href="underscore.js">Development Version (1.4.0)</a></td>
    377. 

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

  378.       </tr>
    379. 

  379.       <tr>
    380. 

  380.         <td><a href="underscore-min.js">Production Version (1.4.0)</a></td>
    381. 

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

  382.       </tr>
    383. 

  383.       <tr>
    384. 

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

  385.       </tr>
    386. 

  386.       <tr>
    387. 

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

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

  389.       </tr>
    390. 

  390.     </table>
    391. 

  391. 

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

  393. 

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

  395. 

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

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

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

  399.         <br />
    400. 

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

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

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

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

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

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

  406.       </p>
    407. 

  407.       <pre>
    408. 

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

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

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

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

  412. 

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

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

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

  416.         <br />
    417. 

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

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

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

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

  421.       </p>
    422. 

  422.       <pre>
    423. 

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

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

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

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

  427. 

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

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

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

  431.         <br />
    432. 

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

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

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

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

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

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

  438.       </p>
    439. 

  439.       <pre>
    440. 

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

  441. =&gt; 6
    442. 

  442. </pre>
    443. 

  443. 

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

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

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

  447.         <br />
    448. 

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

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

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

  451.         evaluation.
    452. 

  452.       </p>
    453. 

  453.       <pre>
    454. 

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

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

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

  457. </pre>
    458. 

  458. 

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

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

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

  462.         <br />
    463. 

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

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

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

  466.         entire list.
    467. 

  467.       </p>
    468. 

  468.       <pre>
    469. 

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

  470. =&gt; 2
    471. 

  471. </pre>
    472. 

  472. 

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

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

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

  476.         <br />
    477. 

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

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

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

  480.       </p>
    481. 

  481.       <pre>
    482. 

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

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

  484. </pre>
    485. 

  485. 

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

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

  488.         <br />
    489. 

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

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

  491.       </p>
    492. 

  492.       <pre>
    493. 

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

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

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

  496. </pre>
    497. 

  497. 

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

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

  500.         <br />
    501. 

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

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

  503.       </p>
    504. 

  504.       <pre>
    505. 

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

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

  507. </pre>
    508. 

  508. 

  509.       <p id="all">
    510. 

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

  511.         <span class="alias">Alias: <b>every</b></span>
    512. 

  512.         <br />
    513. 

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

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

  515.       </p>
    516. 

  516.       <pre>
    517. 

  517. _.all([true, 1, null, 'yes'], _.identity);
    518. 

  518. =&gt; false
    519. 

  519. </pre>
    520. 

  520. 

  521.       <p id="any">
    522. 

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

  523.         <span class="alias">Alias: <b>some</b></span>
    524. 

  524.         <br />
    525. 

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

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

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

  528.         if present.
    529. 

  529.       </p>
    530. 

  530.       <pre>
    531. 

  531. _.any([null, 0, 'yes', false]);
    532. 

  532. =&gt; true
    533. 

  533. </pre>
    534. 

  534. 

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

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

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

  538.         <br />
    539. 

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

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

  541.       </p>
    542. 

  542.       <pre>
    543. 

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

  544. =&gt; true
    545. 

  545. </pre>
    546. 

  546. 

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

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

  549.         <br />
    550. 

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

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

  552.         method invocation.
    553. 

  553.       </p>
    554. 

  554.       <pre>
    555. 

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

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

  557. </pre>
    558. 

  558. 

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

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

  561.         <br />
    562. 

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

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

  564.       </p>
    565. 

  565.       <pre>
    566. 

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

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

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

  569. </pre>
    570. 

  570. 

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

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

  573.         <br />
    574. 

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

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

  576.         value is ranked.
    577. 

  577.       </p>
    578. 

  578.       <pre>
    579. 

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

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

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

  582. </pre>
    583. 

  583. 

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

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

  586.         <br />
    587. 

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

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

  589.         value is ranked.
    590. 

  590.       </p>
    591. 

  591.       <pre>
    592. 

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

  593. _.min(numbers);
    594. 

  594. =&gt; 2
    595. 

  595. </pre>
    596. 

  596. 

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

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

  599.         <br />
    600. 

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

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

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

  603.       </p>
    604. 

  604.       <pre>
    605. 

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

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

  607. </pre>
    608. 

  608. 

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

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

  611.         <br />
    612. 

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

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

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

  615.         the values.
    616. 

  616.       </p>
    617. 

  617.       <pre>
    618. 

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

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

  620. 

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

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

  623. </pre>
    624. 

  624. 

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

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

  627.         <br />
    628. 

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

  629.         in each group.
    630. 

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

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

  632.       </p>
    633. 

  633.       <pre>
    634. 

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

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

  636. });
    637. 

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

  638. </pre>
    639. 

  639. 

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

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

  642.         <br />
    643. 

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

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

  645.       </p>
    646. 

  646.       <pre>
    647. 

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

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

  649. </pre>
    650. 

  650. 

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

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

  653.         <br />
    654. 

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

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

  656.       </p>
    657. 

  657.       <pre>
    658. 

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

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

  660. </pre>
    661. 

  661. 

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

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

  664.         <br />
    665. 

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

  666.       </p>
    667. 

  667.       <pre>
    668. 

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

  669. =&gt; 3
    670. 

  670. </pre>
    671. 

  671. 

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

  673. 

  674.       <p>
    675. 

  675.         <i>
    676. 

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

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

  678.         </i>
    679. 

  679.       </p>
    680. 

  680. 

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

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

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

  684.         <br />
    685. 

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

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

  687.       </p>
    688. 

  688.       <pre>
    689. 

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

  690. =&gt; 5
    691. 

  691. </pre>
    692. 

  692. 

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

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

  695.         <br />
    696. 

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

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

  698.         from the result.
    699. 

  699.       </p>
    700. 

  700.       <pre>
    701. 

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

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

  703. </pre>
    704. 

  704. 

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

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

  707.         <br />
    708. 

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

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

  710.       </p>
    711. 

  711.       <pre>
    712. 

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

  713. =&gt; 1
    714. 

  714. </pre>
    715. 

  715. 

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

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

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

  719.         <br />
    720. 

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

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

  722.       </p>
    723. 

  723.       <pre>
    724. 

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

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

  726. </pre>
    727. 

  727. 

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

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

  730.         <br />
    731. 

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

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

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

  734.       </p>
    735. 

  735.       <pre>
    736. 

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

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

  738. </pre>
    739. 

  739. 

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

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

  742.         <br />
    743. 

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

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

  745.       </p>
    746. 

  746.       <pre>
    747. 

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

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

  749. 

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

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

  752. </pre>
    753. 

  753. 

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

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

  756.         <br />
    757. 

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

  758.         removed.
    759. 

  759.       </p>
    760. 

  760.       <pre>
    761. 

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

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

  763. </pre>
    764. 

  764. 

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

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

  767.         <br />
    768. 

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

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

  770.       </p>
    771. 

  771.       <pre>
    772. 

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

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

  774. </pre>
    775. 

  775. 

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

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

  778.         <br />
    779. 

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

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

  781.       </p>
    782. 

  782.       <pre>
    783. 

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

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

  785. </pre>
    786. 

  786. 

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

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

  789.         <br />
    790. 

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

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

  792.       </p>
    793. 

  793.       <pre>
    794. 

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

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

  796. </pre>
    797. 

  797. 

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

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

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

  801.         <br />
    802. 

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

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

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

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

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

  807.       </p>
    808. 

  808.       <pre>
    809. 

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

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

  811. </pre>
    812. 

  812. 

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

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

  815.         <br />
    816. 

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

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

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

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

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

  821.       </p>
    822. 

  822.       <pre>
    823. 

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

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

  825. </pre>
    826. 

  826. 

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

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

  829.         <br />
    830. 

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

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

  832.       </p>
    833. 

  833.       <pre>
    834. 

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

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

  836. 

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

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

  839. </pre>
    840. 

  840. 

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

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

  843.         <br />
    844. 

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

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

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

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

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

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

  850.         array after the given index.
    851. 

  851.       </p>
    852. 

  852.       <pre>
    853. 

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

  854. =&gt; 1
    855. 

  855. </pre>
    856. 

  856. 

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

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

  859.         <br />
    860. 

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

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

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

  863.         given index.
    864. 

  864.       </p>
    865. 

  865.       <pre>
    866. 

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

  867. =&gt; 4
    868. 

  868. </pre>
    869. 

  869. 

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

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

  872.         <br />
    873. 

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

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

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

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

  877.       </p>
    878. 

  878.       <pre>
    879. 

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

  880. =&gt; 3
    881. 

  881. </pre>
    882. 

  882. 

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

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

  885.         <br />
    886. 

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

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

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

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

  890.         exclusive.
    891. 

  891.       </p>
    892. 

  892.       <pre>
    893. 

  893. _.range(10);
    894. 

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

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

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

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

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

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

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

  901. _.range(0);
    902. 

  902. =&gt; []
    903. 

  903. </pre>
    904. 

  904. 

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

  906. 

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

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

  909.         <br />
    910. 

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

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

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

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

  914.       </p>
    915. 

  915.       <pre>
    916. 

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

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

  918. func();
    919. 

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

  920. </pre>
    921. 

  921. 

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

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

  924.         <br />
    925. 

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

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

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

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

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

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

  931.       </p>
    932. 

  932.       <pre>
    933. 

  933. var buttonView = {
    934. 

  934.   label   : 'underscore',
    935. 

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

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

  937. };
    938. 

  938. _.bindAll(buttonView);
    939. 

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

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

  941. </pre>
    942. 

  942. 

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

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

  945.         <br />
    946. 

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

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

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

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

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

  951.         as the key.
    952. 

  952.       </p>
    953. 

  953.       <pre>
    954. 

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

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

  956. });
    957. 

  957. </pre>
    958. 

  958. 

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

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

  961.         <br />
    962. 

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

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

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

  965.       </p>
    966. 

  966.       <pre>
    967. 

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

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

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

  970. </pre>
    971. 

  971. 

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

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

  974.         <br />
    975. 

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

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

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

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

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

  980.       </p>
    981. 

  981.       <pre>
    982. 

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

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

  984. </pre>
    985. 

  985. 

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

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

  988.         <br />
    989. 

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

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

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

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

  993.         can keep up with.
    994. 

  994.       </p>
    995. 

  995.       <pre>
    996. 

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

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

  998. </pre>
    999. 

  999. 

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

  1001.         <b class="header">debounce</b><code>_.debounce(function, wait, [immediate])</code>
    1002. 

  1002.         <br />
    1003. 

  1003.         Creates and returns a new debounced version of the passed function that
    1004. 

  1004.         will postpone its execution until after
    1005. 

  1005.         <b>wait</b> milliseconds have elapsed since the last time it
    1006. 

  1006.         was invoked. Useful for implementing behavior that should only happen
    1007. 

  1007.         <i>after</i> the input has stopped arriving. For example: rendering a
    1008. 

  1008.         preview of a Markdown comment, recalculating a layout after the window
    1009. 

  1009.         has stopped being resized, and so on.
    1010. 

  1010.       </p>
    1011. 

  1011. 

  1012.       <p>
    1013. 

  1013.         Pass <tt>true</tt> for the <b>immediate</b> parameter to cause
    1014. 

  1014.         <b>debounce</b> to trigger the function on the leading instead of the
    1015. 

  1015.         trailing edge of the <b>wait</b> interval. Useful in circumstances like
    1016. 

  1016.         preventing accidental double-clicks on a "submit" button from firing a
    1017. 

  1017.         second time.
    1018. 

  1018.       </p>
    1019. 

  1019. 

  1020.       <pre>
    1021. 

  1021. var lazyLayout = _.debounce(calculateLayout, 300);
    1022. 

  1022. $(window).resize(lazyLayout);
    1023. 

  1023. </pre>
    1024. 

  1024. 

  1025.       <p id="once">
    1026. 

  1026.         <b class="header">once</b><code>_.once(function)</code>
    1027. 

  1027.         <br />
    1028. 

  1028.         Creates a version of the function that can only be called one time.
    1029. 

  1029.         Repeated calls to the modified function will have no effect, returning
    1030. 

  1030.         the value from the original call. Useful for initialization functions,
    1031. 

  1031.         instead of having to set a boolean flag and then check it later.
    1032. 

  1032.       </p>
    1033. 

  1033.       <pre>
    1034. 

  1034. var initialize = _.once(createApplication);
    1035. 

  1035. initialize();
    1036. 

  1036. initialize();
    1037. 

  1037. // Application is only created once.
    1038. 

  1038. </pre>
    1039. 

  1039. 

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

  1041.         <b class="header">after</b><code>_.after(count, function)</code>
    1042. 

  1042.         <br />
    1043. 

  1043.         Creates a version of the function that will only be run after first
    1044. 

  1044.         being called <b>count</b> times. Useful for grouping asynchronous responses,
    1045. 

  1045.         where you want to be sure that all the async calls have finished, before
    1046. 

  1046.         proceeding.
    1047. 

  1047.       </p>
    1048. 

  1048.       <pre>
    1049. 

  1049. var renderNotes = _.after(notes.length, render);
    1050. 

  1050. _.each(notes, function(note) {
    1051. 

  1051.   note.asyncSave({success: renderNotes});
    1052. 

  1052. });
    1053. 

  1053. // renderNotes is run once, after all notes have saved.
    1054. 

  1054. </pre>
    1055. 

  1055. 

  1056.       <p id="wrap">
    1057. 

  1057.         <b class="header">wrap</b><code>_.wrap(function, wrapper)</code>
    1058. 

  1058.         <br />
    1059. 

  1059.         Wraps the first <b>function</b> inside of the <b>wrapper</b> function,
    1060. 

  1060.         passing it as the first argument. This allows the <b>wrapper</b> to
    1061. 

  1061.         execute code before and after the <b>function</b> runs, adjust the arguments,
    1062. 

  1062.         and execute it conditionally.
    1063. 

  1063.       </p>
    1064. 

  1064.       <pre>
    1065. 

  1065. var hello = function(name) { return "hello: " + name; };
    1066. 

  1066. hello = _.wrap(hello, function(func) {
    1067. 

  1067.   return "before, " + func("moe") + ", after";
    1068. 

  1068. });
    1069. 

  1069. hello();
    1070. 

  1070. =&gt; 'before, hello: moe, after'
    1071. 

  1071. </pre>
    1072. 

  1072. 

  1073.       <p id="compose">
    1074. 

  1074.         <b class="header">compose</b><code>_.compose(*functions)</code>
    1075. 

  1075.         <br />
    1076. 

  1076.         Returns the composition of a list of <b>functions</b>, where each function
    1077. 

  1077.         consumes the return value of the function that follows. In math terms,
    1078. 

  1078.         composing the functions <i>f()</i>, <i>g()</i>, and <i>h()</i> produces
    1079. 

  1079.         <i>f(g(h()))</i>.
    1080. 

  1080.       </p>
    1081. 

  1081.       <pre>
    1082. 

  1082. var greet    = function(name){ return "hi: " + name; };
    1083. 

  1083. var exclaim  = function(statement){ return statement + "!"; };
    1084. 

  1084. var welcome = _.compose(exclaim, greet);
    1085. 

  1085. welcome('moe');
    1086. 

  1086. =&gt; 'hi: moe!'
    1087. 

  1087. </pre>
    1088. 

  1088. 

  1089.       <h2 id="objects">Object Functions</h2>
    1090. 

  1090. 

  1091.       <p id="keys">
    1092. 

  1092.         <b class="header">keys</b><code>_.keys(object)</code>
    1093. 

  1093.         <br />
    1094. 

  1094.         Retrieve all the names of the <b>object</b>'s properties.
    1095. 

  1095.       </p>
    1096. 

  1096.       <pre>
    1097. 

  1097. _.keys({one : 1, two : 2, three : 3});
    1098. 

  1098. =&gt; ["one", "two", "three"]
    1099. 

  1099. </pre>
    1100. 

  1100. 

  1101.       <p id="values">
    1102. 

  1102.         <b class="header">values</b><code>_.values(object)</code>
    1103. 

  1103.         <br />
    1104. 

  1104.         Return all of the values of the <b>object</b>'s properties.
    1105. 

  1105.       </p>
    1106. 

  1106.       <pre>
    1107. 

  1107. _.values({one : 1, two : 2, three : 3});
    1108. 

  1108. =&gt; [1, 2, 3]
    1109. 

  1109. </pre>
    1110. 

  1110. 

  1111.       <p id="pairs">
    1112. 

  1112.         <b class="header">pairs</b><code>_.pairs(object)</code>
    1113. 

  1113.         <br />
    1114. 

  1114.         Convert an object into a list of <tt>[key, value]</tt> pairs.
    1115. 

  1115.       </p>
    1116. 

  1116.       <pre>
    1117. 

  1117. _.pairs({one : 1, two : 2, three : 3});
    1118. 

  1118. =&gt; [[one: 1], [two: 2], [three: 3]]
    1119. 

  1119. </pre>
    1120. 

  1120. 

  1121.       <p id="invert">
    1122. 

  1122.         <b class="header">invert</b><code>_.invert(object)</code>
    1123. 

  1123.         <br />
    1124. 

  1124.         Returns a copy of the <b>object</b> where the keys have become the values
    1125. 

  1125.         and the values the keys. For this to work, all of your object's values 
    1126. 

  1126.         should be unique and string serializable.
    1127. 

  1127.       </p>
    1128. 

  1128.       <pre>
    1129. 

  1129. _.invert({Moe: "Moses", Larry: "Louis", Curly: "Jerome"});
    1130. 

  1130. =&gt; {Moses: "Moe", Louis: "Larry", Jerome: "Curly"};
    1131. 

  1131. </pre>
    1132. 

  1132. 

  1133.       <p id="object-functions">
    1134. 

  1134.         <b class="header">functions</b><code>_.functions(object)</code>
    1135. 

  1135.         <span class="alias">Alias: <b>methods</b></span>
    1136. 

  1136.         <br />
    1137. 

  1137.         Returns a sorted list of the names of every method in an object &mdash;
    1138. 

  1138.         that is to say, the name of every function property of the object.
    1139. 

  1139.       </p>
    1140. 

  1140.       <pre>
    1141. 

  1141. _.functions(_);
    1142. 

  1142. =&gt; ["all", "any", "bind", "bindAll", "clone", "compact", "compose" ...
    1143. 

  1143. </pre>
    1144. 

  1144. 

  1145.       <p id="extend">
    1146. 

  1146.         <b class="header">extend</b><code>_.extend(destination, *sources)</code>
    1147. 

  1147.         <br />
    1148. 

  1148.         Copy all of the properties in the <b>source</b> objects over to the
    1149. 

  1149.         <b>destination</b> object, and return the <b>destination</b> object.
    1150. 

  1150.         It's in-order, so the last source will override properties of the same
    1151. 

  1151.         name in previous arguments.
    1152. 

  1152.       </p>
    1153. 

  1153.       <pre>
    1154. 

  1154. _.extend({name : 'moe'}, {age : 50});
    1155. 

  1155. =&gt; {name : 'moe', age : 50}
    1156. 

  1156. </pre>
    1157. 

  1157. 

  1158.       <p id="pick">
    1159. 

  1159.         <b class="header">pick</b><code>_.pick(object, *keys)</code>
    1160. 

  1160.         <br />
    1161. 

  1161.         Return a copy of the <b>object</b>, filtered to only have values for
    1162. 

  1162.         the whitelisted <b>keys</b> (or array of valid keys).
    1163. 

  1163.       </p>
    1164. 

  1164.       <pre>
    1165. 

  1165. _.pick({name : 'moe', age: 50, userid : 'moe1'}, 'name', 'age');
    1166. 

  1166. =&gt; {name : 'moe', age : 50}
    1167. 

  1167. </pre>
    1168. 

  1168. 

  1169.       <p id="omit">
    1170. 

  1170.         <b class="header">omit</b><code>_.omit(object, *keys)</code>
    1171. 

  1171.         <br />
    1172. 

  1172.         Return a copy of the <b>object</b>, filtered to omit the blacklisted
    1173. 

  1173.         <b>keys</b> (or array of keys).
    1174. 

  1174.       </p>
    1175. 

  1175.       <pre>
    1176. 

  1176. _.omit({name : 'moe', age : 50, userid : 'moe1'}, 'userid');
    1177. 

  1177. =&gt; {name : 'moe', age : 50}
    1178. 

  1178. </pre>
    1179. 

  1179. 

  1180.       <p id="defaults">
    1181. 

  1181.         <b class="header">defaults</b><code>_.defaults(object, *defaults)</code>
    1182. 

  1182.         <br />
    1183. 

  1183.         Fill in null and undefined properties in <b>object</b> with values from the
    1184. 

  1184.         <b>defaults</b> objects, and return the <b>object</b>. As soon as the
    1185. 

  1185.         property is filled, further defaults will have no effect.
    1186. 

  1186.       </p>
    1187. 

  1187.       <pre>
    1188. 

  1188. var iceCream = {flavor : "chocolate"};
    1189. 

  1189. _.defaults(iceCream, {flavor : "vanilla", sprinkles : "lots"});
    1190. 

  1190. =&gt; {flavor : "chocolate", sprinkles : "lots"}
    1191. 

  1191. </pre>
    1192. 

  1192. 

  1193.       <p id="clone">
    1194. 

  1194.         <b class="header">clone</b><code>_.clone(object)</code>
    1195. 

  1195.         <br />
    1196. 

  1196.         Create a shallow-copied clone of the <b>object</b>. Any nested objects
    1197. 

  1197.         or arrays will be copied by reference, not duplicated.
    1198. 

  1198.       </p>
    1199. 

  1199.       <pre>
    1200. 

  1200. _.clone({name : 'moe'});
    1201. 

  1201. =&gt; {name : 'moe'};
    1202. 

  1202. </pre>
    1203. 

  1203. 

  1204.       <p id="tap">
    1205. 

  1205.         <b class="header">tap</b><code>_.tap(object, interceptor)</code>
    1206. 

  1206.         <br />
    1207. 

  1207.         Invokes <b>interceptor</b> with the <b>object</b>, and then returns <b>object</b>.
    1208. 

  1208.         The primary purpose of this method is to "tap into" a method chain, in order to perform operations on intermediate results within the chain.
    1209. 

  1209.       </p>
    1210. 

  1210.       <pre>
    1211. 

  1211. _.chain([1,2,3,200])
    1212. 

  1212.   .filter(function(num) { return num % 2 == 0; })
    1213. 

  1213.   .tap(alert)
    1214. 

  1214.   .map(function(num) { return num * num })
    1215. 

  1215.   .value();
    1216. 

  1216. =&gt; // [2, 200] (alerted)
    1217. 

  1217. =&gt; [4, 40000]
    1218. 

  1218. </pre>
    1219. 

  1219. 

  1220.       <p id="has">
    1221. 

  1221.         <b class="header">has</b><code>_.has(object, key)</code>
    1222. 

  1222.         <br />
    1223. 

  1223.         Does the object contain the given key? Identical to
    1224. 

  1224.         <tt>object.hasOwnProperty(key)</tt>, but uses a safe reference to the
    1225. 

  1225.         <tt>hasOwnProperty</tt> function, in case it's been
    1226. 

  1226.         <a href="http://www.devthought.com/2012/01/18/an-object-is-not-a-hash/">overridden accidentally</a>.
    1227. 

  1227.       </p>
    1228. 

  1228.       <pre>
    1229. 

  1229. _.has({a: 1, b: 2, c: 3}, "b");
    1230. 

  1230. =&gt; true
    1231. 

  1231. </pre>
    1232. 

  1232. 

  1233.       <p id="isEqual">
    1234. 

  1234.         <b class="header">isEqual</b><code>_.isEqual(object, other)</code>
    1235. 

  1235.         <br />
    1236. 

  1236.         Performs an optimized deep comparison between the two objects, to determine
    1237. 

  1237.         if they should be considered equal.
    1238. 

  1238.       </p>
    1239. 

  1239.       <pre>
    1240. 

  1240. var moe   = {name : 'moe', luckyNumbers : [13, 27, 34]};
    1241. 

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

  1242. moe == clone;
    1243. 

  1243. =&gt; false
    1244. 

  1244. _.isEqual(moe, clone);
    1245. 

  1245. =&gt; true
    1246. 

  1246. </pre>
    1247. 

  1247. 

  1248.       <p id="isEmpty">
    1249. 

  1249.         <b class="header">isEmpty</b><code>_.isEmpty(object)</code>
    1250. 

  1250.         <br />
    1251. 

  1251.         Returns <i>true</i> if <b>object</b> contains no values.
    1252. 

  1252.       </p>
    1253. 

  1253.       <pre>
    1254. 

  1254. _.isEmpty([1, 2, 3]);
    1255. 

  1255. =&gt; false
    1256. 

  1256. _.isEmpty({});
    1257. 

  1257. =&gt; true
    1258. 

  1258. </pre>
    1259. 

  1259. 

  1260.       <p id="isElement">
    1261. 

  1261.         <b class="header">isElement</b><code>_.isElement(object)</code>
    1262. 

  1262.         <br />
    1263. 

  1263.         Returns <i>true</i> if <b>object</b> is a DOM element.
    1264. 

  1264.       </p>
    1265. 

  1265.       <pre>
    1266. 

  1266. _.isElement(jQuery('body')[0]);
    1267. 

  1267. =&gt; true
    1268. 

  1268. </pre>
    1269. 

  1269. 

  1270.       <p id="isArray">
    1271. 

  1271.         <b class="header">isArray</b><code>_.isArray(object)</code>
    1272. 

  1272.         <br />
    1273. 

  1273.         Returns <i>true</i> if <b>object</b> is an Array.
    1274. 

  1274.       </p>
    1275. 

  1275.       <pre>
    1276. 

  1276. (function(){ return _.isArray(arguments); })();
    1277. 

  1277. =&gt; false
    1278. 

  1278. _.isArray([1,2,3]);
    1279. 

  1279. =&gt; true
    1280. 

  1280. </pre>
    1281. 

  1281. 

  1282.       <p id="isObject">
    1283. 

  1283.         <b class="header">isObject</b><code>_.isObject(value)</code>
    1284. 

  1284.         <br />
    1285. 

  1285.         Returns <i>true</i> if <b>value</b> is an Object. Note that JavaScript
    1286. 

  1286.         arrays and functions are objects, while (normal) strings and numbers are not.
    1287. 

  1287.       </p>
    1288. 

  1288.       <pre>
    1289. 

  1289. _.isObject({});
    1290. 

  1290. =&gt; true
    1291. 

  1291. _.isObject(1);
    1292. 

  1292. =&gt; false
    1293. 

  1293. </pre>
    1294. 

  1294. 

  1295.       <p id="isArguments">
    1296. 

  1296.         <b class="header">isArguments</b><code>_.isArguments(object)</code>
    1297. 

  1297.         <br />
    1298. 

  1298.         Returns <i>true</i> if <b>object</b> is an Arguments object.
    1299. 

  1299.       </p>
    1300. 

  1300.       <pre>
    1301. 

  1301. (function(){ return _.isArguments(arguments); })(1, 2, 3);
    1302. 

  1302. =&gt; true
    1303. 

  1303. _.isArguments([1,2,3]);
    1304. 

  1304. =&gt; false
    1305. 

  1305. </pre>
    1306. 

  1306. 

  1307.       <p id="isFunction">
    1308. 

  1308.         <b class="header">isFunction</b><code>_.isFunction(object)</code>
    1309. 

  1309.         <br />
    1310. 

  1310.         Returns <i>true</i> if <b>object</b> is a Function.
    1311. 

  1311.       </p>
    1312. 

  1312.       <pre>
    1313. 

  1313. _.isFunction(alert);
    1314. 

  1314. =&gt; true
    1315. 

  1315. </pre>
    1316. 

  1316. 

  1317.       <p id="isString">
    1318. 

  1318.         <b class="header">isString</b><code>_.isString(object)</code>
    1319. 

  1319.         <br />
    1320. 

  1320.         Returns <i>true</i> if <b>object</b> is a String.
    1321. 

  1321.       </p>
    1322. 

  1322.       <pre>
    1323. 

  1323. _.isString("moe");
    1324. 

  1324. =&gt; true
    1325. 

  1325. </pre>
    1326. 

  1326. 

  1327.       <p id="isNumber">
    1328. 

  1328.         <b class="header">isNumber</b><code>_.isNumber(object)</code>
    1329. 

  1329.         <br />
    1330. 

  1330.         Returns <i>true</i> if <b>object</b> is a Number (including <tt>NaN</tt>).
    1331. 

  1331.       </p>
    1332. 

  1332.       <pre>
    1333. 

  1333. _.isNumber(8.4 * 5);
    1334. 

  1334. =&gt; true
    1335. 

  1335. </pre>
    1336. 

  1336. 

  1337.       <p id="isFinite">
    1338. 

  1338.         <b class="header">isFinite</b><code>_.isFinite(object)</code>
    1339. 

  1339.         <br />
    1340. 

  1340.         Returns <i>true</i> if <b>object</b> is a finite Number.
    1341. 

  1341.       </p>
    1342. 

  1342.       <pre>
    1343. 

  1343. _.isFinite(-101);
    1344. 

  1344. =&gt; true
    1345. 

  1345. 

  1346. _.isFinite(-Infinity);
    1347. 

  1347. =&gt; false
    1348. 

  1348. </pre>
    1349. 

  1349. 

  1350.       <p id="isBoolean">
    1351. 

  1351.         <b class="header">isBoolean</b><code>_.isBoolean(object)</code>
    1352. 

  1352.         <br />
    1353. 

  1353.         Returns <i>true</i> if <b>object</b> is either <i>true</i> or <i>false</i>.
    1354. 

  1354.       </p>
    1355. 

  1355.       <pre>
    1356. 

  1356. _.isBoolean(null);
    1357. 

  1357. =&gt; false
    1358. 

  1358. </pre>
    1359. 

  1359. 

  1360.       <p id="isDate">
    1361. 

  1361.         <b class="header">isDate</b><code>_.isDate(object)</code>
    1362. 

  1362.         <br />
    1363. 

  1363.         Returns <i>true</i> if <b>object</b> is a Date.
    1364. 

  1364.       </p>
    1365. 

  1365.       <pre>
    1366. 

  1366. _.isDate(new Date());
    1367. 

  1367. =&gt; true
    1368. 

  1368. </pre>
    1369. 

  1369. 

  1370.       <p id="isRegExp">
    1371. 

  1371.         <b class="header">isRegExp</b><code>_.isRegExp(object)</code>
    1372. 

  1372.         <br />
    1373. 

  1373.         Returns <i>true</i> if <b>object</b> is a RegExp.
    1374. 

  1374.       </p>
    1375. 

  1375.       <pre>
    1376. 

  1376. _.isRegExp(/moe/);
    1377. 

  1377. =&gt; true
    1378. 

  1378. </pre>
    1379. 

  1379. 

  1380.       <p id="isNaN">
    1381. 

  1381.         <b class="header">isNaN</b><code>_.isNaN(object)</code>
    1382. 

  1382.         <br />
    1383. 

  1383.         Returns <i>true</i> if <b>object</b> is <i>NaN</i>.<br /> Note: this is not
    1384. 

  1384.         the same as the native <b>isNaN</b> function, which will also return
    1385. 

  1385.         true if the variable is <i>undefined</i>.
    1386. 

  1386.       </p>
    1387. 

  1387.       <pre>
    1388. 

  1388. _.isNaN(NaN);
    1389. 

  1389. =&gt; true
    1390. 

  1390. isNaN(undefined);
    1391. 

  1391. =&gt; true
    1392. 

  1392. _.isNaN(undefined);
    1393. 

  1393. =&gt; false
    1394. 

  1394. </pre>
    1395. 

  1395. 

  1396.       <p id="isNull">
    1397. 

  1397.         <b class="header">isNull</b><code>_.isNull(object)</code>
    1398. 

  1398.         <br />
    1399. 

  1399.         Returns <i>true</i> if the value of <b>object</b> is <i>null</i>.
    1400. 

  1400.       </p>
    1401. 

  1401.       <pre>
    1402. 

  1402. _.isNull(null);
    1403. 

  1403. =&gt; true
    1404. 

  1404. _.isNull(undefined);
    1405. 

  1405. =&gt; false
    1406. 

  1406. </pre>
    1407. 

  1407. 

  1408.       <p id="isUndefined">
    1409. 

  1409.         <b class="header">isUndefined</b><code>_.isUndefined(value)</code>
    1410. 

  1410.         <br />
    1411. 

  1411.         Returns <i>true</i> if <b>value</b> is <i>undefined</i>.
    1412. 

  1412.       </p>
    1413. 

  1413.       <pre>
    1414. 

  1414. _.isUndefined(window.missingVariable);
    1415. 

  1415. =&gt; true
    1416. 

  1416. </pre>
    1417. 

  1417. 

  1418.       <h2 id="utility">Utility Functions</h2>
    1419. 

  1419. 

  1420.       <p id="noConflict">
    1421. 

  1421.         <b class="header">noConflict</b><code>_.noConflict()</code>
    1422. 

  1422.         <br />
    1423. 

  1423.         Give control of the "_" variable back to its previous owner. Returns
    1424. 

  1424.         a reference to the <b>Underscore</b> object.
    1425. 

  1425.       </p>
    1426. 

  1426.       <pre>
    1427. 

  1427. var underscore = _.noConflict();</pre>
    1428. 

  1428. 

  1429.       <p id="identity">
    1430. 

  1430.         <b class="header">identity</b><code>_.identity(value)</code>
    1431. 

  1431.         <br />
    1432. 

  1432.         Returns the same value that is used as the argument. In math:
    1433. 

  1433.         <tt>f(x) = x</tt><br />
    1434. 

  1434.         This function looks useless, but is used throughout Underscore as
    1435. 

  1435.         a default iterator.
    1436. 

  1436.       </p>
    1437. 

  1437.       <pre>
    1438. 

  1438. var moe = {name : 'moe'};
    1439. 

  1439. moe === _.identity(moe);
    1440. 

  1440. =&gt; true</pre>
    1441. 

  1441. 

  1442.       <p id="times">
    1443. 

  1443.         <b class="header">times</b><code>_.times(n, iterator, [context])</code>
    1444. 

  1444.         <br />
    1445. 

  1445.         Invokes the given iterator function <b>n</b> times. Each invocation of 
    1446. 

  1446.         <b>iterator</b> is called with an <tt>index</tt> argument.
    1447. 

  1447.       </p>
    1448. 

  1448.       <pre>
    1449. 

  1449. _(3).times(function(n){ genie.grantWishNumber(n); });</pre>
    1450. 

  1450. 

  1451.       <p id="random">
    1452. 

  1452.         <b class="header">random</b><code>_.random(min, max)</code>
    1453. 

  1453.         <br />
    1454. 

  1454.         Returns a random integer between <b>min</b> and <b>max</b>, inclusive.
    1455. 

  1455.         If you only pass one argument, it will return a number between <tt>0</tt>
    1456. 

  1456.         and that number.
    1457. 

  1457.       </p>
    1458. 

  1458.       <pre>
    1459. 

  1459. _.random(0, 100);
    1460. 

  1460. =&gt; 42</pre>
    1461. 

  1461. 

  1462.       <p id="mixin">
    1463. 

  1463.         <b class="header">mixin</b><code>_.mixin(object)</code>
    1464. 

  1464.         <br />
    1465. 

  1465.         Allows you to extend Underscore with your own utility functions. Pass
    1466. 

  1466.         a hash of <tt>{name: function}</tt> definitions to have your functions
    1467. 

  1467.         added to the Underscore object, as well as the OOP wrapper.
    1468. 

  1468.       </p>
    1469. 

  1469.       <pre>
    1470. 

  1470. _.mixin({
    1471. 

  1471.   capitalize : function(string) {
    1472. 

  1472.     return string.charAt(0).toUpperCase() + string.substring(1).toLowerCase();
    1473. 

  1473.   }
    1474. 

  1474. });
    1475. 

  1475. _("fabio").capitalize();
    1476. 

  1476. =&gt; "Fabio"
    1477. 

  1477. </pre>
    1478. 

  1478. 

  1479.       <p id="uniqueId">
    1480. 

  1480.         <b class="header">uniqueId</b><code>_.uniqueId([prefix])</code>
    1481. 

  1481.         <br />
    1482. 

  1482.         Generate a globally-unique id for client-side models or DOM elements
    1483. 

  1483.         that need one. If <b>prefix</b> is passed, the id will be appended to it.
    1484. 

  1484.         Without <b>prefix</b>, returns an integer.
    1485. 

  1485.       </p>
    1486. 

  1486.       <pre>
    1487. 

  1487. _.uniqueId('contact_');
    1488. 

  1488. =&gt; 'contact_104'</pre>
    1489. 

  1489. 

  1490.       <p id="escape">
    1491. 

  1491.         <b class="header">escape</b><code>_.escape(string)</code>
    1492. 

  1492.     …
    1493.

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