elsewhere

<!DOCTYPE HTML> <html> <head> <meta http-equiv="content-type" content="text/html;charset=UTF-8" /> <meta http-equiv="X-UA-Compatible" content="chrome=1"> <link rel="shortcut icon" href="favicon.ico" type="image/x-icon" /> <title>Underscore.js</title> <style> body { font-size: 14px; line-height: 22px; background: #f4f4f4 url(docs/images/background.png); color: #000; font-family: Helvetica Neue, Helvetica, Arial; } .interface { font-family: "Lucida Grande", "Lucida Sans Unicode", Helvetica, Arial, sans-serif !important; } div#sidebar { background: #fff; position: fixed; top: 0; left: 0; bottom: 0; width: 200px; overflow-y: auto; overflow-x: hidden; -webkit-overflow-scrolling: touch; padding: 15px 0 30px 30px; border-right: 1px solid #bbb; box-shadow: 0 0 20px #ccc; -webkit-box-shadow: 0 0 20px #ccc; -moz-box-shadow: 0 0 20px #ccc; } a.toc_title, a.toc_title:visited { display: block; color: black; font-weight: bold; margin-top: 15px; } a.toc_title:hover { text-decoration: underline; } #sidebar .version { font-size: 10px; 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font-size: 12px; line-height: 18px; font-style: normal; } tt { padding: 0px 3px; background: #fff; border: 1px solid #ddd; zoom: 1; } code { margin-left: 20px; } pre { font-size: 12px; padding: 2px 0 2px 15px; border-left: 5px solid #bbb; margin: 0px 0 30px; } </style> </head> <body> <div id="sidebar" class="interface"> <a class="toc_title" href="#"> Underscore.js (1.3.3) </a> <a class="toc_title" href="#"> Introduction </a> <a class="toc_title" href="#collections"> Collections </a> <ul class="toc_section"> <li>- <a href="#each">each</a></li> <li>- <a href="#map">map</a></li> <li>- <a href="#reduce">reduce</a></li> <li>- <a href="#reduceRight">reduceRight</a></li> <li>- <a href="#find">find</a></li> <li>- <a href="#filter">filter</a></li> <li>- <a href="#reject">reject</a></li> <li>- <a href="#all">all</a></li> <li>- <a href="#any">any</a></li> <li>- <a href="#include">include</a></li> <li>- <a href="#invoke">invoke</a></li> <li>- <a href="#pluck">pluck</a></li> <li>- <a href="#max">max</a></li> <li>- <a href="#min">min</a></li> <li>- <a href="#sortBy">sortBy</a></li> <li>- <a href="#groupBy">groupBy</a></li> <li>- <a href="#sortedIndex">sortedIndex</a></li> <li>- <a href="#shuffle">shuffle</a></li> <li>- <a href="#toArray">toArray</a></li> <li>- <a href="#size">size</a></li> </ul> <a class="toc_title" href="#arrays"> Arrays </a> <ul class="toc_section"> <li>- <a href="#first">first</a></li> <li>- <a href="#initial">initial</a></li> <li>- <a href="#last">last</a></li> <li>- <a href="#rest">rest</a></li> <li>- <a href="#compact">compact</a></li> <li>- <a href="#flatten">flatten</a></li> <li>- <a href="#without">without</a></li> <li>- <a href="#union">union</a></li> <li>- <a href="#intersection">intersection</a></li> <li>- <a href="#difference">difference</a></li> <li>- <a href="#uniq">uniq</a></li> <li>- <a href="#zip">zip</a></li> <li>- <a href="#indexOf">indexOf</a></li> <li>- <a href="#lastIndexOf">lastIndexOf</a></li> <li>- <a href="#range">range</a></li> </ul> <a class="toc_title" href="#functions"> Functions </a> <ul class="toc_section"> <li>- <a href="#bind">bind</a></li> <li>- <a href="#bindAll">bindAll</a></li> <li>- <a href="#memoize">memoize</a></li> <li>- <a href="#delay">delay</a></li> <li>- <a href="#defer">defer</a></li> <li>- <a href="#throttle">throttle</a></li> <li>- <a href="#debounce">debounce</a></li> <li>- <a href="#once">once</a></li> <li>- <a href="#after">after</a></li> <li>- <a href="#wrap">wrap</a></li> <li>- <a href="#compose">compose</a></li> </ul> <a class="toc_title" href="#objects"> Objects </a> <ul class="toc_section"> <li>- <a href="#keys">keys</a></li> <li>- <a href="#values">values</a></li> <li>- <a href="#object-functions">functions</a></li> <li>- <a href="#extend">extend</a></li> <li>- <a href="#pick">pick</a></li> <li>- <a href="#defaults">defaults</a></li> <li>- <a href="#clone">clone</a></li> <li>- <a href="#tap">tap</a></li> <li>- <a href="#has">has</a></li> <li>- <a href="#isEqual">isEqual</a></li> <li>- <a href="#isEmpty">isEmpty</a></li> <li>- <a href="#isElement">isElement</a></li> <li>- <a href="#isArray">isArray</a></li> <li>- <a href="#isObject">isObject</a></li> <li>- <a href="#isArguments">isArguments</a></li> <li>- <a href="#isFunction">isFunction</a></li> <li>- <a href="#isString">isString</a></li> <li>- <a href="#isNumber">isNumber</a></li> <li>- <a href="#isFinite">isFinite</a></li> <li>- <a href="#isBoolean">isBoolean</a></li> <li>- <a href="#isDate">isDate</a></li> <li>- <a href="#isRegExp">isRegExp</a></li> <li>- <a href="#isNaN">isNaN</a></li> <li>- <a href="#isNull">isNull</a></li> <li>- <a href="#isUndefined">isUndefined</a></li> </ul> <a class="toc_title" href="#utility"> Utility </a> <ul class="toc_section"> <li>- <a href="#noConflict">noConflict</a></li> <li>- <a href="#identity">identity</a></li> <li>- <a href="#times">times</a></li> <li>- <a href="#mixin">mixin</a></li> <li>- <a href="#uniqueId">uniqueId</a></li> <li>- <a href="#escape">escape</a></li> <li>- <a href="#result">result</a></li> <li>- <a href="#template">template</a></li> </ul> <a class="toc_title" href="#chaining"> Chaining </a> <ul class="toc_section"> <li>- <a href="#chain">chain</a></li> <li>- <a href="#value">value</a></li> </ul> <a class="toc_title" href="#links"> Links </a> <a class="toc_title" href="#changelog"> Change Log </a> </div> <div class="container"> <img style="width: 396px; height: 69px;" src="docs/images/underscore.png" alt="Underscore.js" /> <a href="http://github.com/documentcloud/underscore/">Underscore</a> is a utility-belt library for JavaScript that provides a lot of the functional programming support that you would expect in <a href="http://prototypejs.org/api">Prototype.js</a> (or <a href="http://www.ruby-doc.org/core/classes/Enumerable.html">Ruby</a>), but without extending any of the built-in JavaScript objects. It's the tie to go along with <a href="http://docs.jquery.com">jQuery</a>'s tux, and <a href="http://backbonejs.org">Backbone.js</a>'s suspenders. Underscore provides 60-odd functions that support both the usual functional suspects: map, select, invoke — as well as more specialized helpers: function binding, javascript templating, deep equality testing, and so on. It delegates to built-in functions, if present, so modern browsers will use the native implementations of forEach, map, reduce, filter, every, some and indexOf. A complete <a href="test/test.html">Test & Benchmark Suite</a> is included for your perusal. You may also read through the <a href="docs/underscore.html">annotated source code</a>. The project is <a href="http://github.com/documentcloud/underscore/">hosted on GitHub</a>. You can report bugs and discuss features on the <a href="http://github.com/documentcloud/underscore/issues">issues page</a>, on Freenode in the <tt>#documentcloud</tt> channel, or send tweets to <a href="http://twitter.com/documentcloud">@documentcloud</a>. Underscore is an open-source component of <a href="http://documentcloud.org/">DocumentCloud</a>. <h2>Downloads (Right-click, and use "Save As")</h2> <table> <tr> <td><a href="underscore.js">Development Version (1.3.3)</a></td> <td>37kb, Uncompressed with Plentiful Comments</td> </tr> <tr> <td><a href="underscore-min.js">Production Version (1.3.3)</a></td> <td>4kb, Minified and Gzipped</td> </tr> </table> <div class="warning">Upgrade warning: versions 1.3.0 and higher remove AMD (RequireJS) support.</div> <div id="documentation"> <h2 id="collections">Collection Functions (Arrays or Objects)</h2> each<code>_.each(list, iterator, [context])</code> Alias: forEach Iterates over a list of elements, yielding each in turn to an iterator function. The iterator is bound to the context object, if one is passed. Each invocation of iterator is called with three arguments: <tt>(element, index, list)</tt>. If list is a JavaScript object, iterator's arguments will be <tt>(value, key, list)</tt>. Delegates to the native forEach function if it exists. <pre> _.each([1, 2, 3], function(num){ alert(num); }); => alerts each number in turn... _.each({one : 1, two : 2, three : 3}, function(num, key){ alert(num); }); => alerts each number in turn...</pre> map<code>_.map(list, iterator, [context])</code> Alias: collect Produces a new array of values by mapping each value in list through a transformation function (iterator). If the native map method exists, it will be used instead. If list is a JavaScript object, iterator's arguments will be <tt>(value, key, list)</tt>. <pre> _.map([1, 2, 3], function(num){ return num * 3; }); => [3, 6, 9] _.map({one : 1, two : 2, three : 3}, function(num, key){ return num * 3; }); => [3, 6, 9]</pre> reduce<code>_.reduce(list, iterator, memo, [context])</code> Aliases: inject, foldl Also known as inject and foldl, reduce boils down a list of values into a single value. Memo is the initial state of the reduction, and each successive step of it should be returned by iterator. <pre> var sum = _.reduce([1, 2, 3], function(memo, num){ return memo + num; }, 0); => 6 </pre> reduceRight<code>_.reduceRight(list, iterator, memo, [context])</code> Alias: foldr The right-associative version of reduce. Delegates to the JavaScript 1.8 version of reduceRight, if it exists. Foldr is not as useful in JavaScript as it would be in a language with lazy evaluation. <pre> var list = [[0, 1], [2, 3], [4, 5]]; var flat = _.reduceRight(list, function(a, b) { return a.concat(b); }, []); => [4, 5, 2, 3, 0, 1] </pre> find<code>_.find(list, iterator, [context])</code> Alias: detect Looks through each value in the list, returning the first one that passes a truth test (iterator). The function returns as soon as it finds an acceptable element, and doesn't traverse the entire list. <pre> var even = _.find([1, 2, 3, 4, 5, 6], function(num){ return num % 2 == 0; }); => 2 </pre> filter<code>_.filter(list, iterator, [context])</code> Alias: select Looks through each value in the list, returning an array of all the values that pass a truth test (iterator). Delegates to the native filter method, if it exists. <pre> var evens = _.filter([1, 2, 3, 4, 5, 6], function(num){ return num % 2 == 0; }); => [2, 4, 6] </pre> reject<code>_.reject(list, iterator, [context])</code> Returns the values in list without the elements that the truth test (iterator) passes. The opposite of filter. <pre> var odds = _.reject([1, 2, 3, 4, 5, 6], function(num){ return num % 2 == 0; }); => [1, 3, 5] </pre> all<code>_.all(list, iterator, [context])</code> Alias: every Returns true if all of the values in the list pass the iterator truth test. Delegates to the native method every, if present. <pre> _.all([true, 1, null, 'yes'], _.identity); => false </pre> any<code>_.any(list, [iterator], [context])</code> Alias: some Returns true if any of the values in the list pass the iterator truth test. Short-circuits and stops traversing the list if a true element is found. Delegates to the native method some, if present. <pre> _.any([null, 0, 'yes', false]); => true </pre> include<code>_.include(list, value)</code> Alias: contains Returns true if the value is present in the list, using === to test equality. Uses indexOf internally, if list is an Array. <pre> _.include([1, 2, 3], 3); => true </pre> invoke<code>_.invoke(list, methodName, [*arguments])</code> Calls the method named by methodName on each value in the list. Any extra arguments passed to invoke will be forwarded on to the method invocation. <pre> _.invoke([[5, 1, 7], [3, 2, 1]], 'sort'); => [[1, 5, 7], [1, 2, 3]] </pre> pluck<code>_.pluck(list, propertyName)</code> A convenient version of what is perhaps the most common use-case for map: extracting a list of property values. <pre> var stooges = [{name : 'moe', age : 40}, {name : 'larry', age : 50}, {name : 'curly', age : 60}]; _.pluck(stooges, 'name'); => ["moe", "larry", "curly"] </pre> max<code>_.max(list, [iterator], [context])</code> Returns the maximum value in list. If iterator is passed, it will be used on each value to generate the criterion by which the value is ranked. <pre> var stooges = [{name : 'moe', age : 40}, {name : 'larry', age : 50}, {name : 'curly', age : 60}]; _.max(stooges, function(stooge){ return stooge.age; }); => {name : 'curly', age : 60}; </pre> min<code>_.min(list, [iterator], [context])</code> Returns the minimum value in list. If iterator is passed, it will be used on each value to generate the criterion by which the value is ranked. <pre> var numbers = [10, 5, 100, 2, 1000]; _.min(numbers); => 2 </pre> sortBy<code>_.sortBy(list, iterator, [context])</code> Returns a sorted copy of list, ranked in ascending order by the results of running each value through iterator. Iterator may also be the string name of the property to sort by (eg. <tt>length</tt>). <pre> _.sortBy([1, 2, 3, 4, 5, 6], function(num){ return Math.sin(num); }); => [5, 4, 6, 3, 1, 2] </pre> groupBy<code>_.groupBy(list, iterator)</code> Splits a collection into sets, grouped by the result of running each value through iterator. If iterator is a string instead of a function, groups by the property named by iterator on each of the values. <pre> _.groupBy([1.3, 2.1, 2.4], function(num){ return Math.floor(num); }); => {1: [1.3], 2: [2.1, 2.4]} _.groupBy(['one', 'two', 'three'], 'length'); => {3: ["one", "two"], 5: ["three"]} </pre> sortedIndex<code>_.sortedIndex(list, value, [iterator])</code> Uses a binary search to determine the index at which the value should be inserted into the list in order to maintain the list's sorted order. If an iterator is passed, it will be used to compute the sort ranking of each value. <pre> _.sortedIndex([10, 20, 30, 40, 50], 35); => 3 </pre> shuffle<code>_.shuffle(list)</code> Returns a shuffled copy of the list, using a version of the <a href="http://en.wikipedia.org/wiki/Fisher%E2%80%93Yates_shuffle">Fisher-Yates shuffle</a>. <pre> _.shuffle([1, 2, 3, 4, 5, 6]); => [4, 1, 6, 3, 5, 2] </pre> toArray<code>_.toArray(list)</code> Converts the list (anything that can be iterated over), into a real Array. Useful for transmuting the arguments object. <pre> (function(){ return _.toArray(arguments).slice(1); })(1, 2, 3, 4); => [2, 3, 4] </pre> size<code>_.size(list)</code> Return the number of values in the list. <pre> _.size({one : 1, two : 2, three : 3}); => 3 </pre> <h2 id="arrays">Array Functions</h2> Note: All array functions will also work on the arguments object. first<code>_.first(array, [n])</code> Alias: head Returns the first element of an array. Passing n will return the first n elements of the array. <pre> _.first([5, 4, 3, 2, 1]); => 5 </pre> initial<code>_.initial(array, [n])</code> Returns everything but the last entry of the array. Especially useful on the arguments object. Pass n to exclude the last n elements from the result. <pre> _.initial([5, 4, 3, 2, 1]); => [5, 4, 3, 2] </pre> last<code>_.last(array, [n])</code> Returns the last element of an array. Passing n will return the last n elements of the array. <pre> _.last([5, 4, 3, 2, 1]); => 1 </pre> rest<code>_.rest(array, [index])</code> Alias: tail Returns the rest of the elements in an array. Pass an index to return the values of the array from that index onward. <pre> _.rest([5, 4, 3, 2, 1]); => [4, 3, 2, 1] </pre> compact<code>_.compact(array)</code> Returns a copy of the array with all falsy values removed. In JavaScript, false, null, 0, "", undefined and NaN are all falsy. <pre> _.compact([0, 1, false, 2, '', 3]); => [1, 2, 3] </pre> flatten<code>_.flatten(array, [shallow])</code> Flattens a nested array (the nesting can be to any depth). If you pass shallow, the array will only be flattened a single level. <pre> _.flatten([1, [2], [3, [[4]]]]); => [1, 2, 3, 4]; _.flatten([1, [2], [3, [[4]]]], true); => [1, 2, 3, [[4]]]; </pre> without<code>_.without(array, [*values])</code> Returns a copy of the array with all instances of the values removed. === is used for the equality test. <pre> _.without([1, 2, 1, 0, 3, 1, 4], 0, 1); => [2, 3, 4] </pre> union<code>_.union(*arrays)</code> Computes the union of the passed-in arrays: the list of unique items, in order, that are present in one or more of the arrays. <pre> _.union([1, 2, 3], [101, 2, 1, 10], [2, 1]); => [1, 2, 3, 101, 10] </pre> intersection<code>_.intersection(*arrays)</code> Computes the list of values that are the intersection of all the arrays. Each value in the result is present in each of the arrays. <pre> _.intersection([1, 2, 3], [101, 2, 1, 10], [2, 1]); => [1, 2] </pre> difference<code>_.difference(array, *others)</code> Similar to without, but returns the values from array that are not present in the other arrays. <pre> _.difference([1, 2, 3, 4, 5], [5, 2, 10]); => [1, 3, 4] </pre> uniq<code>_.uniq(array, [isSorted], [iterator])</code> Alias: unique Produces a duplicate-free version of the array, using === to test object equality. If you know in advance that the array is sorted, passing true for isSorted will run a much faster algorithm. If you want to compute unique items based on a transformation, pass an iterator function. <pre> _.uniq([1, 2, 1, 3, 1, 4]); => [1, 2, 3, 4] </pre> zip<code>_.zip(*arrays)</code> Merges together the values of each of the arrays with the values at the corresponding position. Useful when you have separate data sources that are coordinated through matching array indexes. If you're working with a matrix of nested arrays, zip.apply can transpose the matrix in a similar fashion. <pre> _.zip(['moe', 'larry', 'curly'], [30, 40, 50], [true, false, false]); => [["moe", 30, true], ["larry", 40, false], ["curly", 50, false]] </pre> indexOf<code>_.indexOf(array, value, [isSorted])</code> Returns the index at which value can be found in the array, or -1 if value is not present in the array. Uses the native indexOf function unless it's missing. If you're working with a large array, and you know that the array is already sorted, pass <tt>true</tt> for isSorted to use a faster binary search. <pre> _.indexOf([1, 2, 3], 2); => 1 </pre> lastIndexOf<code>_.lastIndexOf(array, value)</code> Returns the index of the last occurrence of value in the array, or -1 if value is not present. Uses the native lastIndexOf function if possible. <pre> _.lastIndexOf([1, 2, 3, 1, 2, 3], 2); => 4 </pre> range<code>_.range([start], stop, [step])</code> A function to create flexibly-numbered lists of integers, handy for <tt>each</tt> and <tt>map</tt> loops. start, if omitted, defaults to 0; step defaults to 1. Returns a list of integers from start to stop, incremented (or decremented) by step, exclusive. <pre> _.range(10); => [0, 1, 2, 3, 4, 5, 6, 7, 8, 9] _.range(1, 11); => [1, 2, 3, 4, 5, 6, 7, 8, 9, 10] _.range(0, 30, 5); => [0, 5, 10, 15, 20, 25] _.range(0, -10, -1); => [0, -1, -2, -3, -4, -5, -6, -7, -8, -9] _.range(0); => [] </pre> <h2 id="functions">Function (uh, ahem) Functions</h2> bind<code>_.bind(function, object, [*arguments])</code> Bind a function to an object, meaning that whenever the function is called, the value of this will be the object. Optionally, bind arguments to the function to pre-fill them, also known as partial application. <pre> var func = function(greeting){ return greeting + ': ' + this.name }; func = _.bind(func, {name : 'moe'}, 'hi'); func(); => 'hi: moe' </pre> bindAll<code>_.bindAll(object, [*methodNames])</code> Binds a number of methods on the object, specified by methodNames, to be run in the context of that object whenever they are invoked. Very handy for binding functions that are going to be used as event handlers, which would otherwise be invoked with a fairly useless this. If no methodNames are provided, all of the object's function properties will be bound to it. <pre> var buttonView = { label : 'underscore', onClick : function(){ alert('clicked: ' + this.label); }, onHover : function(){ console.log('hovering: ' + this.label); } }; _.bindAll(buttonView); jQuery('#underscore_button').bind('click', buttonView.onClick); => When the button is clicked, this.label will have the correct value... </pre> memoize<code>_.memoize(function, [hashFunction])</code> Memoizes a given function by caching the computed result. Useful for speeding up slow-running computations. If passed an optional hashFunction, it will be used to compute the hash key for storing the result, based on the arguments to the original function. The default hashFunction just uses the first argument to the memoized function as the key. <pre> var fibonacci = _.memoize(function(n) { return n < 2 ? n : fibonacci(n - 1) + fibonacci(n - 2); }); </pre> delay<code>_.delay(function, wait, [*arguments])</code> Much like setTimeout, invokes function after wait milliseconds. If you pass the optional arguments, they will be forwarded on to the function when it is invoked. <pre> var log = _.bind(console.log, console); _.delay(log, 1000, 'logged later'); => 'logged later' // Appears after one second. </pre> defer<code>_.defer(function)</code> Defers invoking the function until the current call stack has cleared, similar to using setTimeout with a delay of 0. Useful for performing expensive computations or HTML rendering in chunks without blocking the UI thread from updating. <pre> _.defer(function(){ alert('deferred'); }); // Returns from the function before the alert runs. </pre> throttle<code>_.throttle(function, wait)</code> Creates and returns a new, throttled version of the passed function, that, when invoked repeatedly, will only actually call the original function at most once per every wait milliseconds. Useful for rate-limiting events that occur faster than you can keep up with. <pre> var throttled = _.throttle(updatePosition, 100); $(window).scroll(throttled); </pre> debounce<code>_.debounce(function, wait, [immediate])</code> Creates and returns a new debounced version of the passed function that will postpone its execution until after wait milliseconds have elapsed since the last time it was invoked. Useful for implementing behavior that should only happen after the input has stopped arriving. For example: rendering a preview of a Markdown comment, recalculating a layout after the window has stopped being resized, and so on. Pass <tt>true</tt> for the immediate parameter to cause debounce to trigger the function on the leading intead of the trailing edge of the wait interval. Useful in circumstances like preventing accidental double-clicks on a "submit" button from firing a second time. <pre> var lazyLayout = _.debounce(calculateLayout, 300); $(window).resize(lazyLayout); </pre> once<code>_.once(function)</code> Creates a version of the function that can only be called one time. Repeated calls to the modified function will have no effect, returning the value from the original call. Useful for initialization functions, instead of having to set a boolean flag and then check it later. <pre> var initialize = _.once(createApplication); initialize(); initialize(); // Application is only created once. </pre> after<code>_.after(count, function)</code> Creates a version of the function that will only be run after first being called count times. Useful for grouping asynchronous responses, where you want to be sure that all the async calls have finished, before proceeding. <pre> var renderNotes = _.after(notes.length, render); _.each(notes, function(note) { note.asyncSave({success: renderNotes}); }); // renderNotes is run once, after all notes have saved. </pre> wrap<code>_.wrap(function, wrapper)</code> Wraps the first function inside of the wrapper function, passing it as the first argument. This allows the wrapper to execute code before and after the function runs, adjust the arguments, and execute it conditionally. <pre> var hello = function(name) { return "hello: " + name; }; hello = _.wrap(hello, function(func) { return "before, " + func("moe") + ", after"; }); hello(); => 'before, hello: moe, after' </pre> compose<code>_.compose(*functions)</code> Returns the composition of a list of functions, where each function consumes the return value of the function that follows. In math terms, composing the functions f(), g(), and h() produces f(g(h())). <pre> var greet = function(name){ return "hi: " + name; }; var exclaim = function(statement){ return statement + "!"; }; var welcome = _.compose(exclaim, greet); welcome('moe'); => 'hi: moe!' </pre> <h2 id="objects">Object Functions</h2> keys<code>_.keys(object)</code> Retrieve all the names of the object's properties. <pre> _.keys({one : 1, two : 2, three : 3}); => ["one", "two", "three"] </pre> values<code>_.values(object)</code> Return all of the values of the object's properties. <pre> _.values({one : 1, two : 2, three : 3}); => [1, 2, 3] </pre> functions<code>_.functions(object)</code> Alias: methods Returns a sorted list of the names of every method in an object — that is to say, the name of every function property of the object. <pre> _.functions(_); => ["all", "any", "bind", "bindAll", "clone", "compact", "compose" ... </pre> extend<code>_.extend(destination, *sources)</code> Copy all of the properties in the source objects over to the destination object, and return the destination object. It's in-order, so the last source will override properties of the same name in previous arguments. <pre> _.extend({name : 'moe'}, {age : 50}); => {name : 'moe', age : 50} </pre> pick<code>_.pick(object, *keys)</code> Return a copy of the object, filtered to only have values for the whitelisted keys (or array of valid keys). <pre> _.pick({name : 'moe', age: 50, userid : 'moe1'}, 'name', 'age'); => {name : 'moe', age : 50} </pre> defaults<code>_.defaults(object, *defaults)</code> Fill in missing properties in object with default values from the defaults objects, and return the object. As soon as the property is filled, further defaults will have no effect. <pre> var iceCream = {flavor : "chocolate"}; _.defaults(iceCream, {flavor : "vanilla", sprinkles : "lots"}); => {flavor : "chocolate", sprinkles : "lots"} </pre> clone<code>_.clone(object)</code> Create a shallow-copied clone of the object. Any nested objects or arrays will be copied by reference, not duplicated. <pre> _.clone({name : 'moe'}); => {name : 'moe'}; </pre> tap<code>_.tap(object, interceptor)</code> Invokes interceptor with the object, and then returns object. The primary purpose of this method is to "tap into" a method chain, in order to perform operations on intermediate results within the chain. <pre> _.chain([1,2,3,200]) .filter(function(num) { return num % 2 == 0; }) .tap(alert) .map(function(num) { return num * num }) .value(); => // [2, 200] (alerted) => [4, 40000] </pre> has<code>_.has(object, key)</code> Does the object contain the given key? Identical to <tt>object.hasOwnProperty(key)</tt>, but uses a safe reference to the <tt>hasOwnProperty</tt> function, in case it's been <a href="http://www.devthought.com/2012/01/18/an-object-is-not-a-hash/">overridden accidentally</a>. <pre> _.has({a: 1, b: 2, c: 3}, "b"); => true </pre> isEqual<code>_.isEqual(object, other)</code> Performs an optimized deep comparison between the two objects, to determine if they should be considered equal. <pre> var moe = {name : 'moe', luckyNumbers : [13, 27, 34]}; var clone = {name : 'moe', luckyNumbers : [13, 27, 34]}; moe == clone; => false _.isEqual(moe, clone); => true </pre> isEmpty<code>_.isEmpty(object)</code> Returns true if object contains no values. <pre> _.isEmpty([1, 2, 3]); => false _.isEmpty({}); => true </pre> isElement<code>_.isElement(object)</code> Returns true if object is a DOM element. <pre> _.isElement(jQuery('body')[0]); => true </pre> isArray<code>_.isArray(object)</code> Returns true if object is an Array. <pre> (function(){ return _.isArray(arguments); })(); => false _.isArray([1,2,3]); => true </pre> isObject<code>_.isObject(value)</code> Returns true if value is an Object. <pre> _.isObject({}); => true _.isObject(1); => false </pre> isArguments<code>_.isArguments(object)</code> Returns true if object is an Arguments object. <pre> (function(){ return _.isArguments(arguments); })(1, 2, 3); => true _.isArguments([1,2,3]); => false </pre> isFunction<code>_.isFunction(object)</code> Returns true if object is a Function. <pre> _.isFunction(alert); => true </pre> isString<code>_.isString(object)</code> Returns true if object is a String. <pre> _.isString("moe"); => true </pre> isNumber<code>_.isNumber(object)</code> Returns true if object is a Number (including <tt>NaN</tt>). <pre> _.isNumber(8.4 * 5); => true </pre> isFinite<code>_.isFinite(object)</code> Returns true if object is a finite Number. <pre> _.isFinite(-101); => true _.isFinite(-Infinity); => false </pre> isBoolean<code>_.isBoolean(object)</code> Returns true if object is either true or false. <pre> _.isBoolean(null); => false </pre> isDate<code>_.isDate(object)</code> Returns true if object is a Date. <pre> _.isDate(new Date()); => true </pre> isRegExp<code>_.isRegExp(object)</code> Returns true if object is a RegExp. <pre> _.isRegExp(/moe/); => true </pre> isNaN<code>_.isNaN(object)</code> Returns true if object is NaN. Note: this is not the same as the native isNaN function, which will also return true if the variable is undefined. <pre> _.isNaN(NaN); => true isNaN(undefined); => true _.isNaN(undefined); => false </pre> isNull<code>_.isNull(object)</code> Returns true if the value of object is null. <pre> _.isNull(null); => true _.isNull(undefined); => false </pre> isUndefined<code>_.isUndefined(variable)</code> Returns true if variable is undefined. <pre> _.isUndefined(window.missingVariable); => true </pre> <h2 id="utility">Utility Functions</h2> noConflict<code>_.noConflict()</code> Give control of the "_" variable back to its previous owner. Returns a reference to the Underscore object. <pre> var underscore = _.noConflict();</pre> identity<code>_.identity(value)</code> Returns the same value that is used as the argument. In math: <tt>f(x) = x</tt> This function looks useless, but is used throughout Underscore as a default iterator. <pre> var moe = {name : 'moe'}; moe === _.identity(moe); => true</pre> times<code>_.times(n, iterator)</code> Invokes the given iterator function n times. <pre> _(3).times(function(){ genie.grantWish(); });</pre> mixin<code>_.mixin(object)</code> Allows you to extend Underscore with your own utility functions. Pass a hash of <tt>{name: function}</tt> definitions to have your functions added to the Underscore object, as well as the OOP wrapper. <pre> _.mixin({ capitalize : function(string) { return string.charAt(0).toUpperCase() + string.substring(1).toLowerCase(); } }); _("fabio").capitalize(); => "Fabio" </pre> uniqueId<code>_.uniqueId([prefix])</code> Generate a globally-unique id for client-side models or DOM elements that need one. If prefix is passed, the id will be appended to it. Without prefix, returns an integer. <pre> _.uniqueId('contact_'); => 'contact_104'</pre> escape<code>_.escape(string)</code> Escapes a string for insertion into HTML, replacing <tt>&</tt>, <tt><</tt>, <tt>></tt>, <tt>"</tt>, <tt>'</tt>, and <tt>/</tt> characters. <pre> _.escape('Curly, Larry & Moe'); => "Curly, Larry &amp; Moe"</pre> result<code>_.result(object, property)</code> If the value of the named property is a function then invoke it; otherwise, return it. <pre> var object = {cheese: 'crumpets', stuff: function(){ return 'nonsense'; }}; _.result(object, 'cheese'); => "crumpets" _.result(object, 'stuff'); => "nonsense"</pre> template<code>_.template(templateString, [data], [settings])</code> Compiles JavaScript templates into functions that can be evaluated for rendering. Useful for rendering complicated bits of HTML from JSON data sources. Template functions can both interpolate variables, using <tt><%= … %></tt>, as well as execute arbitrary JavaScript code, with <tt><% … %></tt>. If you wish to interpolate a value, and have it be HTML-escaped, use <tt><%- … %></tt> When you evaluate a template function, pass in a data object that has properties corresponding to the template's free variables. If you're writing a one-off, you can pass the data object as the second parameter to template in order to render immediately instead of returning a template function. The settings argument should be a hash containing any <tt>_.templateSettings</tt> that should be overriden. <pre> var compiled = _.template("hello: <%= name %>"); compiled({name : 'moe'}); => "hello: moe" var list = "<% _.each(people, function(name) { %> <li><%= name %></li> <% }); %>"; _.template(list, {people : ['moe', 'curly', 'larry']}); => "<li>moe</li><li>curly</li><li>larry</li>" var template = _.template("<%- value %>"); template({value : '<script>'}); => "&lt;script&gt;"</pre> You can also use <tt>print</tt> from within JavaScript code. This is sometimes more convenient than using <tt><%= ... %></tt>. <pre> var compiled = _.template("<% print('Hello ' + epithet); %>"); compiled({epithet: "stooge"}); => "Hello stooge."</pre> If ERB-style delimiters aren't your cup of tea, you can change Underscore's template settings to use different symbols to set off interpolated code. Define an interpolate regex to match expressions that should be interpolated verbatim, an escape regex to match expressions that should be inserted after being HTML escaped, and an evaluate regex to match expressions that should be evaluated without insertion into the resulting string. You may define or omit any combination of the three. For example, to perform <a href="http://github.com/janl/mustache.js#readme">Mustache.js</a> style templating: <pre> _.templateSettings = { interpolate : /\{\{(.+?)\}\}/g }; var template = _.template("Hello {{ name }}!"); template({name : "Mustache"}); => "Hello Mustache!"</pre> By default, template places the values from your data in the local scope via the <tt>with</tt> statement. However, you can specify a single variable name with the variable setting. This can significantly improve the speed at which a template is able to render. <pre> _.template("<%= data.hasWith %>", {hasWith: 'no'}, {variable: 'data'}); => "no"</pre> Precompiling your templates can be a big help when debugging errors you can't reproduce. This is because precompiled templates can provide line numbers and a stack trace, something that is not possible when compiling templates on the client. The source property is available on the compiled template function for easy precompilation. <pre><script> JST.project = <%= _.template(jstText).source %>; </script></pre> <h2 id="chaining">Chaining</h2> You can use Underscore in either an object-oriented or a functional style, depending on your preference. The following two lines of code are identical ways to double a list of numbers. <pre> _.map([1, 2, 3], function(n){ return n * 2; }); _([1, 2, 3]).map(function(n){ return n * 2; });</pre> Calling <tt>chain</tt> on a wrapped object will cause all future method calls to return wrapped objects as well. When you've finished the computation, use <tt>value</tt> to retrieve the final value. Here's an example of chaining together a map/flatten/reduce, in order to get the word count of every word in a song. <pre> var lyrics = [ {line : 1, words : "I'm a