 
    
Underscore is a JavaScript library that provides a whole mess of useful functional programming helpers without extending any built-in objects. It’s the answer to the question: “If I sit down in front of a blank HTML page, and want to start being productive immediately, what do I need?” … and the tie to go along with jQuery's tux and Backbone's suspenders.
Underscore provides over 100 functions that support both your favorite workaday functional helpers: map, filter, invoke — as well as more specialized goodies: function binding, javascript templating, creating quick indexes, deep equality testing, and so on.
A complete Test Suite is included for your perusal.
You may also read through the annotated source code. There is a modular version with clickable import references as well.
You may choose between monolithic and modular imports. There is a quick summary of the options below, as well as a more comprehensive discussion in the article.
Enjoying Underscore, and want to turn it up to 11? Try Underscore-contrib.
The project is hosted on GitHub. You can report bugs and discuss features on the issues page or chat in the Gitter channel.
You can support the project by donating on Patreon. Enterprise coverage is available as part of the Tidelift Subscription.
Underscore is an open-source component of DocumentCloud.
| ESM (Development) | 65.9 KB, Uncompressed with Plentiful Comments (Source Map) | 
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| UMD (Development) | 68.4 KB, Uncompressed with Bountiful Comments (Source Map) | 
| UMD (Production) | 7.48 KB, Minified and Gzipped (Source Map) | 
| Edge ESM | Unreleased, current master, use by your own judgement and at your own risk | 
| Edge UMD | Unreleased, current master, use if you’re feeling lucky | 
      In most cases, you can replace the version number above by
      latest so that your embed will automatically use the latest
      version, or stable if you want to delay updating until an update
      has proven to be free of accidental breaking changes. Example:
      https://cdn.jsdelivr.net/npm/underscore@latest/underscore-umd-min.js
    
If you are hardcoding the path to the file within the package and you are unsure which build to use, it is very likely that you need underscore-umd.js or the minified variant underscore-umd-min.js.
For functions with multiple aliases, the file name of the module is always the first name that appears in the documentation. For example, _.reduce/_.inject/_.foldl is exported from underscore/modules/reduce.js. Modular usage is mostly recommended for creating a customized build of Underscore.
Underscore 1.x is backwards compatible with any engine that fully supports ES3, while also utilizing newer features when available, such as Object.keys, typed arrays and ES modules. We routinely run our unittests against the JavaScript engines listed below:
In addition:
Underscore 2.x will likely remove support for some outdated environments.
        each_.each(list, iteratee, [context])
        Alias: forEach
        source
        
        Iterates over a list of elements, yielding each in turn to an
        iteratee function.
        The iteratee is bound to the context object, if one is
        passed. Each invocation of iteratee is called with three arguments:
        (element, index, list). If list is a JavaScript object, iteratee's
        arguments will be (value, key, list). Returns the list for chaining.
      
_.each([1, 2, 3], alert);
=> alerts each number in turn...
_.each({one: 1, two: 2, three: 3}, alert);
=> alerts each number value in turn...
      Note: Collection functions work on arrays, objects, and array-like objects such as arguments, NodeList and similar. But it works by duck-typing, so avoid passing objects with a numeric length property. It's also good to note that an each loop cannot be broken out of — to break, use _.find instead.
        map_.map(list, iteratee, [context])
        Alias: collect
        source
        
        Produces a new array of values by mapping each value in list
        through a transformation function (iteratee).
        The iteratee is passed three arguments: the value,
        then the index (or key) of the iteration,
        and finally a reference to the entire list.
      
_.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]
_.map([[1, 2], [3, 4]], _.first);
=> [1, 3]
      
        reduce_.reduce(list, iteratee, [memo], [context])
        Aliases: inject, foldl
        source
        
        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
        iteratee. The iteratee is passed four arguments: the memo, then the value and
        index (or key) of the iteration, and finally a reference to the entire list.
      
If no memo is passed to the initial invocation of reduce, the iteratee is not invoked on the first element of the list. The first element is instead passed as the memo in the invocation of the iteratee on the next element in the list.
var sum = _.reduce([1, 2, 3], function(memo, num){ return memo + num; }, 0);
=> 6
      
        reduceRight_.reduceRight(list, iteratee, [memo], [context])
        Alias: foldr
        source
        
        The right-associative version of reduce. Foldr
        is not as useful in JavaScript as it would be in a language with lazy
        evaluation.
      
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]
      
        find_.find(list, predicate, [context])
        Alias: detect
        source
        
        Looks through each value in the list, returning the first one that
        passes a truth test (predicate), or undefined if no value
        passes the test. The function returns as
        soon as it finds an acceptable element, and doesn't traverse the
        entire list.
        predicate is transformed through iteratee
        to facilitate shorthand syntaxes.
      
var even = _.find([1, 2, 3, 4, 5, 6], function(num){ return num % 2 == 0; });
=> 2
      
        filter_.filter(list, predicate, [context])
        Alias: select
        source
        
        Looks through each value in the list, returning an array of all
        the values that pass a truth test (predicate).
        predicate is transformed through iteratee
        to facilitate shorthand syntaxes.
      
var evens = _.filter([1, 2, 3, 4, 5, 6], function(num){ return num % 2 == 0; });
=> [2, 4, 6]
      
        findWhere_.findWhere(list, properties)
        source
        
        Looks through the list and returns the first value that matches
        all of the key-value pairs listed in properties.
      
If no match is found, or if list is empty, undefined will be returned.
_.findWhere(publicServicePulitzers, {newsroom: "The New York Times"});
=> {year: 1918, newsroom: "The New York Times",
  reason: "For its public service in publishing in full so many official reports,
  documents and speeches by European statesmen relating to the progress and
  conduct of the war."}
      
        where_.where(list, properties)
        source
        
        Looks through each value in the list, returning an array of all
        the values that matches the key-value pairs listed in properties.
      
_.where(listOfPlays, {author: "Shakespeare", year: 1611});
=> [{title: "Cymbeline", author: "Shakespeare", year: 1611},
    {title: "The Tempest", author: "Shakespeare", year: 1611}]
      
        reject_.reject(list, predicate, [context])
        source
        
        Returns the values in list without the elements that the truth
        test (predicate) passes. The opposite of filter.
        predicate is transformed through iteratee
        to facilitate shorthand syntaxes.
      
var odds = _.reject([1, 2, 3, 4, 5, 6], function(num){ return num % 2 == 0; });
=> [1, 3, 5]
      
        every_.every(list, [predicate], [context])
        Alias: all
        source
        
        Returns true if all of the values in the list pass the
        predicate truth test. Short-circuits and stops traversing the list
        if a false element is found.
        predicate is transformed through iteratee
        to facilitate shorthand syntaxes.
      
_.every([2, 4, 5], function(num) { return num % 2 == 0; });
=> false
      
        some_.some(list, [predicate], [context])
        Alias: any
        source
        
        Returns true if any of the values in the list pass the
        predicate truth test. Short-circuits and stops traversing the list
        if a true element is found.
        predicate is transformed through iteratee
        to facilitate shorthand syntaxes.
      
_.some([null, 0, 'yes', false]); => true
        contains_.contains(list, value, [fromIndex])
        Aliases: include, includes
        source
        
        Returns true if the value is present in the list.
        Uses indexOf internally, if list is an Array.
        Use fromIndex to start your search at a given index.
      
_.contains([1, 2, 3], 3); => true
        invoke_.invoke(list, methodName, *arguments)
        source
        
        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.
      
_.invoke([[5, 1, 7], [3, 2, 1]], 'sort'); => [[1, 5, 7], [1, 2, 3]]
        pluck_.pluck(list, propertyName)
        source
        
        A convenient version of what is perhaps the most common use-case for
        map: extracting a list of property values.
      
var stooges = [{name: 'moe', age: 40}, {name: 'larry', age: 50}, {name: 'curly', age: 60}];
_.pluck(stooges, 'name');
=> ["moe", "larry", "curly"]
      
        max_.max(list, [iteratee], [context])
        source
        
        Returns the maximum value in list. If an iteratee
        function is provided, it will be used on each value to generate the
        criterion by which the value is ranked. -Infinity is returned
        if list is empty, so an isEmpty guard
        may be required. This function can currently only compare numbers reliably.
        This function uses operator <
        (note).
      
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};
      
        min_.min(list, [iteratee], [context])
        source
        
        Returns the minimum value in list. If an iteratee
        function is provided, it will be used on each value to generate the
        criterion by which the value is ranked. Infinity is returned
        if list is empty, so an isEmpty guard
        may be required. This function can currently only compare numbers reliably.
        This function uses operator <
        (note).
      
var numbers = [10, 5, 100, 2, 1000]; _.min(numbers); => 2
        sortBy_.sortBy(list, iteratee, [context])
        source
        
        Returns a (stably) sorted copy of list, ranked in ascending
        order by the results of running each value through iteratee.
        iteratee may also be the string name of the property to sort by (eg.
        length). This function uses operator <
        (note).
      
_.sortBy([1, 2, 3, 4, 5, 6], function(num){ return Math.sin(num); });
=> [5, 4, 6, 3, 1, 2]
var stooges = [{name: 'moe', age: 40}, {name: 'larry', age: 50}, {name: 'curly', age: 60}];
_.sortBy(stooges, 'name');
=> [{name: 'curly', age: 60}, {name: 'larry', age: 50}, {name: 'moe', age: 40}];
      
        groupBy_.groupBy(list, iteratee, [context])
        source
        
        Splits a collection into sets, grouped by the result of running each
        value through iteratee. If iteratee is a string instead of
        a function, groups by the property named by iteratee on each of
        the values.
      
_.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"]}
      
        indexBy_.indexBy(list, iteratee, [context])
        source
        
        Given a list, and an iteratee function
        that returns a key for each element in the list (or a property name),
        returns an object with an index of each item.
        Just like groupBy, but for when you know your
        keys are unique.
      
var stooges = [{name: 'moe', age: 40}, {name: 'larry', age: 50}, {name: 'curly', age: 60}];
_.indexBy(stooges, 'age');
=> {
  "40": {name: 'moe', age: 40},
  "50": {name: 'larry', age: 50},
  "60": {name: 'curly', age: 60}
}
      
        countBy_.countBy(list, iteratee, [context])
        source
        
        Sorts a list into groups and returns a count for the number of objects
        in each group.
        Similar to groupBy, but instead of returning a list of values,
        returns a count for the number of values in that group.
      
_.countBy([1, 2, 3, 4, 5], function(num) {
  return num % 2 == 0 ? 'even': 'odd';
});
=> {odd: 3, even: 2}
      
        shuffle_.shuffle(list)
        source
        
        Returns a shuffled copy of the list, using a version of the
        Fisher-Yates shuffle.
      
_.shuffle([1, 2, 3, 4, 5, 6]); => [4, 1, 6, 3, 5, 2]
        sample_.sample(list, [n])
        source
        
        Produce a random sample from the list. Pass a number to
        return n random elements from the list. Otherwise a single random
        item will be returned.
      
_.sample([1, 2, 3, 4, 5, 6]); => 4 _.sample([1, 2, 3, 4, 5, 6], 3); => [1, 6, 2]
        toArray_.toArray(list)
        source
        
        Creates a real Array from the list (anything that can be
        iterated over).  Useful for transmuting the arguments object.
      
(function(){ return _.toArray(arguments).slice(1); })(1, 2, 3, 4);
=> [2, 3, 4]
      
        size_.size(list)
        source
        
        Return the number of values in the list.
      
_.size([1, 2, 3, 4, 5]);
=> 5
_.size({one: 1, two: 2, three: 3});
=> 3
      
        partition_.partition(list, predicate)
        source
        
        Split list into two arrays: one whose elements all satisfy
        predicate and one whose elements all do not satisfy predicate.
        predicate is transformed through iteratee
        to facilitate shorthand syntaxes.
      
_.partition([0, 1, 2, 3, 4, 5], isOdd); => [[1, 3, 5], [0, 2, 4]]
        compact_.compact(list)
        source
        
        Returns a copy of the list with all falsy values removed.
        In JavaScript, false, null, 0, "",
        undefined and NaN are all falsy.
      
_.compact([0, 1, false, 2, '', 3]); => [1, 2, 3]
Note: All array functions will also work on the arguments object. However, Underscore functions are not designed to work on "sparse" arrays.
        first_.first(array, [n])
        Aliases: head, take
        source
        
        Returns the first element of an array. Passing n will
        return the first n elements of the array.
      
_.first([5, 4, 3, 2, 1]); => 5
        initial_.initial(array, [n])
        source
        
        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.
      
_.initial([5, 4, 3, 2, 1]); => [5, 4, 3, 2]
        last_.last(array, [n])
        source
        
        Returns the last element of an array. Passing n will return
        the last n elements of the array.
      
_.last([5, 4, 3, 2, 1]); => 1
        rest_.rest(array, [index])
        Aliases: tail, drop
        source
        
        Returns the rest of the elements in an array. Pass an index
        to return the values of the array from that index onward.
      
_.rest([5, 4, 3, 2, 1]); => [4, 3, 2, 1]
        flatten_.flatten(array, [depth])
        source
        
        Flattens a nested array. If you pass true or 1
        as the depth, the array will only be flattened a single level.
        Passing a greater number will cause the flattening to descend deeper
        into the nesting hierarchy. Omitting the depth argument, or
        passing false or Infinity, flattens the array all the
        way to the deepest nesting level.
      
_.flatten([1, [2], [3, [[4]]]]); => [1, 2, 3, 4]; _.flatten([1, [2], [3, [[4]]]], true); => [1, 2, 3, [[4]]]; _.flatten([1, [2], [3, [[4]]]], 2); => [1, 2, 3, [4]];
        without_.without(array, *values)
        source
        
        Returns a copy of the array with all instances of the values
        removed.
      
_.without([1, 2, 1, 0, 3, 1, 4], 0, 1); => [2, 3, 4]
        union_.union(*arrays)
        source
        
        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.
      
_.union([1, 2, 3], [101, 2, 1, 10], [2, 1]); => [1, 2, 3, 101, 10]
        intersection_.intersection(*arrays)
        source
        
        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.
      
_.intersection([1, 2, 3], [101, 2, 1, 10], [2, 1]); => [1, 2]
        difference_.difference(array, *others)
        source
        
        Similar to without, but returns the values from array that
        are not present in the other arrays.
      
_.difference([1, 2, 3, 4, 5], [5, 2, 10]); => [1, 3, 4]
        uniq_.uniq(array, [isSorted], [iteratee])
        Alias: unique
        source
        
        Produces a duplicate-free version of the array, using === to test
        object equality. In particular only the first occurrence of each value is kept.
        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
        iteratee function.
      
_.uniq([1, 2, 1, 4, 1, 3]); => [1, 2, 4, 3]
        zip_.zip(*arrays)
        source
        
        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.
      
_.zip(['moe', 'larry', 'curly'], [30, 40, 50], [true, false, false]); => [["moe", 30, true], ["larry", 40, false], ["curly", 50, false]]
        unzip_.unzip(array)
        Alias: transpose
        source
        
        The opposite of zip. Given an array of
        arrays, returns a series of new arrays, the first of which contains all
        of the first elements in the input arrays, the second of which contains
        all of the second elements, and so on. If you're working with a matrix
        of nested arrays, this can be used to transpose the matrix.
      
_.unzip([["moe", 30, true], ["larry", 40, false], ["curly", 50, false]]); => [['moe', 'larry', 'curly'], [30, 40, 50], [true, false, false]]
        object_.object(list, [values])
        source
        
        Converts arrays into objects. Pass either a single list of
        [key, value] pairs, or a list of keys, and a list of values. Passing
        by pairs is the reverse of pairs. If duplicate keys exist,
        the last value wins.
      
_.object(['moe', 'larry', 'curly'], [30, 40, 50]);
=> {moe: 30, larry: 40, curly: 50}
_.object([['moe', 30], ['larry', 40], ['curly', 50]]);
=> {moe: 30, larry: 40, curly: 50}
      
        chunk_.chunk(array, length)
        source
        
        Chunks an array into multiple arrays, each containing length
        or fewer items.
      
var partners = _.chunk(_.shuffle(kindergarten), 2); => [["Tyrone", "Elie"], ["Aidan", "Sam"], ["Katrina", "Billie"], ["Little Timmy"]]
        indexOf_.indexOf(array, value, [isSorted])
        source
        
        Returns the index at which value can be found in the array,
        or -1 if value is not present in the array. If you're working with a
        large array, and you know that the array is already sorted, pass true
        for isSorted to use a faster binary search ... or, pass a number as
        the third argument in order to look for the first matching value in the
        array after the given index. If isSorted is true,
        this function uses operator <
        (note).
      
_.indexOf([1, 2, 3], 2); => 1
        lastIndexOf_.lastIndexOf(array, value, [fromIndex])
        source
        
        Returns the index of the last occurrence of value in the array,
        or -1 if value is not present. Pass fromIndex to start your search at a
        given index.
      
_.lastIndexOf([1, 2, 3, 1, 2, 3], 2); => 4
        sortedIndex_.sortedIndex(array, value, [iteratee], [context])
        source
        
        Uses a binary search to determine the smallest index at which the value
        should be inserted into the array in order to maintain the array's
        sorted order. If an iteratee function is provided,
        it will be used to compute the sort ranking of each value, including the value you pass.
        The iteratee may also be the string name of the property to sort by
        (eg. length). This function uses operator <
        (note).
      
_.sortedIndex([10, 20, 30, 40, 50], 35);
=> 3
var stooges = [{name: 'moe', age: 40}, {name: 'curly', age: 60}];
_.sortedIndex(stooges, {name: 'larry', age: 50}, 'age');
=> 1
      
        findIndex_.findIndex(array, predicate, [context])
        source
        
        Similar to _.indexOf, returns the first index
        where the predicate truth test passes; otherwise returns -1.
      
_.findIndex([4, 6, 8, 12], isPrime); => -1 // not found _.findIndex([4, 6, 7, 12], isPrime); => 2
        findLastIndex_.findLastIndex(array, predicate, [context])
        source
        
        Like _.findIndex but iterates the array in reverse,
        returning the index closest to the end where the predicate truth test
        passes.
      
var users = [{'id': 1, 'name': 'Bob', 'last': 'Brown'},
             {'id': 2, 'name': 'Ted', 'last': 'White'},
             {'id': 3, 'name': 'Frank', 'last': 'James'},
             {'id': 4, 'name': 'Ted', 'last': 'Jones'}];
_.findLastIndex(users, {
  name: 'Ted'
});
=> 3
      
        range_.range([start], stop, [step])
        source
        
        A function to create flexibly-numbered lists of integers, handy for
        each and map loops. start, if omitted,
        defaults to 0; step defaults to 1 if start
        is before stop, otherwise -1. Returns a list
        of integers from start (inclusive) to stop (exclusive),
        incremented (or decremented) by step.
      
_.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); => []
        bind_.bind(function, object, *arguments)
        source
        
        Bind a function to an object, meaning that whenever
        the function is called, the value of this will be the object.
        Optionally, pass arguments to the function to pre-fill them,
        also known as partial application. For partial application without
        context binding, use partial.
      
var func = function(greeting){ return greeting + ': ' + this.name };
func = _.bind(func, {name: 'moe'}, 'hi');
func();
=> 'hi: moe'
      
        bindAll_.bindAll(object, *methodNames)
        source
        
        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. methodNames are required.
      
var buttonView = {
  label  : 'underscore',
  onClick: function(){ alert('clicked: ' + this.label); },
  onHover: function(){ console.log('hovering: ' + this.label); }
};
_.bindAll(buttonView, 'onClick', 'onHover');
// When the button is clicked, this.label will have the correct value.
jQuery('#underscore_button').on('click', buttonView.onClick);
      
        partial_.partial(function, *arguments)
        source
        
        Partially apply a function by filling in any number of its
        arguments, without changing its dynamic this
        value. A close cousin of bind. You may pass
        _ in your list of arguments to specify an argument that
        should not be pre-filled, but left open to supply at call-time.
        Note: if you need _ placeholders and a this
        binding at the same time, use both _.partial and
        _.bind.
      
var subtract = function(a, b) { return b - a; };
sub5 = _.partial(subtract, 5);
sub5(20);
=> 15
// Using a placeholder
subFrom20 = _.partial(subtract, _, 20);
subFrom20(5);
=> 15
      
        memoize_.memoize(function, [hashFunction])
        source
        
        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. The cache of memoized values is available as the cache
        property on the returned function.
      
var fibonacci = _.memoize(function(n) {
  return n < 2 ? n: fibonacci(n - 1) + fibonacci(n - 2);
});
      
        delay_.delay(function, wait, *arguments)
        source
        
        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.
      
var log = _.bind(console.log, console); _.delay(log, 1000, 'logged later'); => 'logged later' // Appears after one second.
        defer_.defer(function, *arguments)
        source
        
        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. If you pass the optional arguments, they will be
        forwarded on to the function when it is invoked.
      
_.defer(function(){ alert('deferred'); });
// Returns from the function before the alert runs.
      
        throttle_.throttle(function, wait, [options])
        source
        
        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.
      
        By default, throttle will execute the function as soon as you call it
        for the first time, and, if you call it again any number of times
        during the wait period, as soon as that period is over.
        If you'd like to disable the leading-edge
        call, pass {leading: false}, and if you'd like to disable the
        execution on the trailing-edge, pass 
 {trailing: false}.
      
var throttled = _.throttle(updatePosition, 100); $(window).scroll(throttled);
If you need to cancel a scheduled throttle, you can call .cancel() on the throttled function.
        debounce_.debounce(function, wait, [immediate])
        source
        
        Creates and returns a new debounced version of the passed function which
        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.
      
At the end of the wait interval, the function will be called with the arguments that were passed most recently to the debounced function.
Pass true for the immediate argument to cause debounce to trigger the function on the leading instead 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.
var lazyLayout = _.debounce(calculateLayout, 300); $(window).resize(lazyLayout);
If you need to cancel a scheduled debounce, you can call .cancel() on the debounced function.
        once_.once(function)
        source
        
        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.
      
var initialize = _.once(createApplication); initialize(); initialize(); // Application is only created once.
        after_.after(count, function)
        source
        
        Creates a wrapper of function that does nothing at first. From
        the count-th call onwards, it starts actually calling
        function. Useful for grouping asynchronous responses, where you
        want to be sure that all the async calls have finished, before
        proceeding.
      
var renderNotes = _.after(notes.length, render);
_.each(notes, function(note) {
  note.asyncSave({success: renderNotes});
});
// renderNotes is run once, after all notes have saved.
      
        before_.before(count, function)
        source
        
        Creates a wrapper of function that memoizes its return value.
        From the count-th call onwards, the memoized result of the last
        invocation is returned immediately instead of invoking function
        again. So the wrapper will invoke function at most count
        - 1 times.
      
var monthlyMeeting = _.before(3, askForRaise); monthlyMeeting(); monthlyMeeting(); monthlyMeeting(); // the result of any subsequent calls is the same as the second call
        wrap_.wrap(function, wrapper)
        source
        
        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.
      
var hello = function(name) { return "hello: " + name; };
hello = _.wrap(hello, function(func) {
  return "before, " + func("moe") + ", after";
});
hello();
=> 'before, hello: moe, after'
      
        negate_.negate(predicate)
        source
        
        Returns a new negated version of the predicate function.
      
var isFalsy = _.negate(Boolean); _.find([-2, -1, 0, 1, 2], isFalsy); => 0
        compose_.compose(*functions)
        source
        
        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())).
      
var greet    = function(name){ return "hi: " + name; };
var exclaim  = function(statement){ return statement.toUpperCase() + "!"; };
var welcome = _.compose(greet, exclaim);
welcome('moe');
=> 'hi: MOE!'
      
        restArguments_.restArguments(function, [startIndex])
        source
        
        Returns a version of the function that, when called, receives all
        arguments from and beyond startIndex collected into a single array.
        If you don’t pass an explicit startIndex, it will be determined by
        looking at the number of arguments to the function itself. Similar
        to ES6’s rest
        parameters syntax.
      
var raceResults = _.restArguments(function(gold, silver, bronze, everyoneElse) {
  _.each(everyoneElse, sendConsolations);
});
raceResults("Dopey", "Grumpy", "Happy", "Sneezy", "Bashful", "Sleepy", "Doc");
      
        keys_.keys(object)
        source
        
        Retrieve all the names of the object's own enumerable properties.
      
_.keys({one: 1, two: 2, three: 3});
=> ["one", "two", "three"]
      
        allKeys_.allKeys(object)
        source
        
        Retrieve all the names of object's own and inherited properties.
      
function Stooge(name) {
  this.name = name;
}
Stooge.prototype.silly = true;
_.allKeys(new Stooge("Moe"));
=> ["name", "silly"]
      
        values_.values(object)
        source
        
        Return all of the values of the object's own properties.
      
_.values({one: 1, two: 2, three: 3});
=> [1, 2, 3]
        mapObject_.mapObject(object, iteratee, [context])
        source
        
        Like map, but for objects. Transform the value
        of each property in turn.
      
_.mapObject({start: 5, end: 12}, function(val, key) {
  return val + 5;
});
=> {start: 10, end: 17}
      
        pairs_.pairs(object)
        source
        
        Convert an object into a list of [key, value] pairs. The opposite
        of object.
      
_.pairs({one: 1, two: 2, three: 3});
=> [["one", 1], ["two", 2], ["three", 3]]
      
        invert_.invert(object)
        source
        
        Returns a copy of the object where the keys have become the values
        and the values the keys. For this to work, all of your object's values
        should be unique and string serializable.
      
_.invert({Moe: "Moses", Larry: "Louis", Curly: "Jerome"});
=> {Moses: "Moe", Louis: "Larry", Jerome: "Curly"};
      
        create_.create(prototype, props)
        source
        
        Creates a new object with the given prototype, optionally attaching
        props as own properties. Basically, Object.create,
        but without all of the property descriptor jazz.
      
var moe = _.create(Stooge.prototype, {name: "Moe"});
      
        functions_.functions(object)
        Alias: methods
        source
        
        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.
      
_.functions(_); => ["all", "any", "bind", "bindAll", "clone", "compact", "compose" ...
        findKey_.findKey(object, predicate, [context])
        source
        
        Similar to _.findIndex but for keys in objects.
        Returns the key where the predicate truth test
        passes or undefined.
        predicate is transformed through iteratee
        to facilitate shorthand syntaxes.
      
        extend_.extend(destination, *sources)
        source
        
        Shallowly copy all of the properties in the source objects over to the
        destination object, and return the destination object.
        Any nested objects or arrays will be copied by reference, not duplicated.
        It's in-order, so the last source will override properties of the same
        name in previous arguments.
      
_.extend({name: 'moe'}, {age: 50});
=> {name: 'moe', age: 50}
      
        extendOwn_.extendOwn(destination, *sources)
        Alias: assign
        source
        
        Like extend, but only copies own properties over to the
        destination object.
      
        pick_.pick(object, *keys)
        source
        
        Return a copy of the object, filtered to only have values for
        the allowed keys (or array of valid keys).  Alternatively
        accepts a predicate indicating which keys to pick.
      
_.pick({name: 'moe', age: 50, userid: 'moe1'}, 'name', 'age');
=> {name: 'moe', age: 50}
_.pick({name: 'moe', age: 50, userid: 'moe1'}, function(value, key, object) {
  return _.isNumber(value);
});
=> {age: 50}
      
        omit_.omit(object, *keys)
        source
        
        Return a copy of the object, filtered to omit the disallowed
        keys (or array of keys).  Alternatively accepts a predicate
        indicating which keys to omit.
      
_.omit({name: 'moe', age: 50, userid: 'moe1'}, 'userid');
=> {name: 'moe', age: 50}
_.omit({name: 'moe', age: 50, userid: 'moe1'}, function(value, key, object) {
  return _.isNumber(value);
});
=> {name: 'moe', userid: 'moe1'}
      
        defaults_.defaults(object, *defaults)
        source
        
        Returns object after filling in its undefined properties
        with the first value present in the following list of defaults objects.
      
var iceCream = {flavor: "chocolate"};
_.defaults(iceCream, {flavor: "vanilla", sprinkles: "lots"});
=> {flavor: "chocolate", sprinkles: "lots"}
      
        clone_.clone(object)
        source
        
        Create a shallow-copied clone of the provided plain object.
        Any nested objects or arrays will be copied by reference, not duplicated.
      
_.clone({name: 'moe'});
=> {name: 'moe'};
      
        tap_.tap(object, interceptor)
        source
        
        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.
      
_.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]
      
        toPath_.toPath(path)
        source
        
        Ensures that path is an array. If path is a string, it is
        wrapped in a single-element array; if it is an array already, it is
        returned unmodified.
      
_.toPath('key');
=> ['key']
_.toPath(['a', 0, 'b']);
=> ['a', 0, 'b'] // (same array)
      _.toPath is used internally in has, get, invoke, property, propertyOf and result, as well as in iteratee and all functions that depend on it, in order to normalize deep property paths. You can override _.toPath if you want to customize this behavior, for example to enable Lodash-like string path shorthands. Be advised that altering _.toPath will unavoidably cause some keys to become unreachable; override at your own risk.
// Support dotted path shorthands.
var originalToPath = _.toPath;
_.mixin({
  toPath: function(path) {
    return _.isString(path) ? path.split('.') : originalToPath(path);
  }
});
_.get({a: [{b: 5}]}, 'a.0.b');
=> 5
      
        get_.get(object, path, [default])
        source
        
        Returns the specified property of object. path may be
        specified as a simple key, or as an array of object keys or array
        indexes, for deep property fetching. If the property does not exist or
        is undefined, the optional default is returned.
      
_.get({a: 10}, 'a');
=> 10
_.get({a: [{b: 2}]}, ['a', 0, 'b']);
=> 2
_.get({a: 10}, 'b', 100);
=> 100
      
        has_.has(object, key)
        source
        
        Does the object contain the given key? Identical to
        object.hasOwnProperty(key), but uses a safe reference to the
        hasOwnProperty function, in case it's been
        overridden accidentally.
      
_.has({a: 1, b: 2, c: 3}, "b");
=> true
      
        property_.property(path)
        source
        
        Returns a function that will return the specified property of any
        passed-in object. path may be specified as a simple key, or
        as an array of object keys or array indexes, for deep property fetching.
      
var stooge = {name: 'moe'};
'moe' === _.property('name')(stooge);
=> true
var stooges = {moe: {fears: {worst: 'Spiders'}}, curly: {fears: {worst: 'Moe'}}};
var curlysWorstFear = _.property(['curly', 'fears', 'worst']);
curlysWorstFear(stooges);
=> 'Moe'
      
        propertyOf_.propertyOf(object)
        source
        
        Inverse of _.property. Takes an object and returns a function
        which will return the value of a provided property.
      
var stooge = {name: 'moe'};
_.propertyOf(stooge)('name');
=> 'moe'
      
        matcher_.matcher(attrs)
        Alias: matches
        source
        
        Returns a predicate function that will tell you if a passed in object
        contains all of the key/value properties present in attrs.
      
var ready = _.matcher({selected: true, visible: true});
var readyToGoList = _.filter(list, ready);
      
        isEqual_.isEqual(object, other)
        source
        
        Performs an optimized deep comparison between the two objects, to determine
        if they should be considered equal.
      
var stooge = {name: 'moe', luckyNumbers: [13, 27, 34]};
var clone  = {name: 'moe', luckyNumbers: [13, 27, 34]};
stooge == clone;
=> false
_.isEqual(stooge, clone);
=> true
      
        isMatch_.isMatch(object, properties)
        source
        
        Tells you if the keys and values in properties are contained
        in object.
      
var stooge = {name: 'moe', age: 32};
_.isMatch(stooge, {age: 32});
=> true
      
        isEmpty_.isEmpty(collection)
        source
        
        Returns true if collection has no elements. For strings
        and array-like objects _.isEmpty checks if the length property
        is 0. For other objects, it returns true if the object has no
        enumerable own-properties. Note that primitive numbers, booleans and
        symbols are always empty by this definition.
      
_.isEmpty([1, 2, 3]);
=> false
_.isEmpty({});
=> true
      
        isElement_.isElement(object)
        source
        
        Returns true if object is a DOM element.
      
_.isElement(jQuery('body')[0]);
=> true
      
        isArray_.isArray(object)
        source
        
        Returns true if object is an Array.
      
(function(){ return _.isArray(arguments); })();
=> false
_.isArray([1,2,3]);
=> true
      
        isObject_.isObject(value)
        source
        
        Returns true if value is an Object. Note that JavaScript
        arrays and functions are objects, while (normal) strings and numbers are not.
      
_.isObject({});
=> true
_.isObject(1);
=> false
      
        isArguments_.isArguments(object)
        source
        
        Returns true if object is an Arguments object.
      
(function(){ return _.isArguments(arguments); })(1, 2, 3);
=> true
_.isArguments([1,2,3]);
=> false
      
        isFunction_.isFunction(object)
        source
        
        Returns true if object is a Function.
      
_.isFunction(alert); => true
        isString_.isString(object)
        source
        
        Returns true if object is a String.
      
_.isString("moe");
=> true
      
        isNumber_.isNumber(object)
        source
        
        Returns true if object is a Number (including NaN).
      
_.isNumber(8.4 * 5); => true
        isFinite_.isFinite(object)
        source
        
        Returns true if object is a finite Number.
      
_.isFinite(-101); => true _.isFinite(-Infinity); => false
        isBoolean_.isBoolean(object)
        source
        
        Returns true if object is either true or false.
      
_.isBoolean(null); => false
        isDate_.isDate(object)
        source
        
        Returns true if object is a Date.
      
_.isDate(new Date()); => true
        isRegExp_.isRegExp(object)
        source
        
        Returns true if object is a RegExp.
      
_.isRegExp(/moe/); => true
        isError_.isError(object)
        source
        
        Returns true if object inherits from an Error.
      
try {
  throw new TypeError("Example");
} catch (o_O) {
  _.isError(o_O);
}
=> true
      
        isSymbol_.isSymbol(object)
        source
        
        Returns true if object is a Symbol.
      
_.isSymbol(Symbol()); => true
        isMap_.isMap(object)
        source
        
        Returns true if object is a Map.
      
_.isMap(new Map()); => true
        isWeakMap_.isWeakMap(object)
        source
        
        Returns true if object is a WeakMap.
      
_.isWeakMap(new WeakMap()); => true
        isSet_.isSet(object)
        source
        
        Returns true if object is a Set.
      
_.isSet(new Set()); => true
        isWeakSet_.isWeakSet(object)
        source
        
        Returns true if object is a WeakSet.
      
_.isWeakSet(WeakSet()); => true
        isArrayBuffer_.isArrayBuffer(object)
        source
        
        Returns true if object is an ArrayBuffer.
      
_.isArrayBuffer(new ArrayBuffer(8)); => true
        isDataView_.isDataView(object)
        source
        
        Returns true if object is a DataView.
      
_.isDataView(new DataView(new ArrayBuffer(8))); => true
        isTypedArray_.isTypedArray(object)
        source
        
        Returns true if object is a TypedArray.
      
_.isTypedArray(new Int8Array(8)); => true
        isNaN_.isNaN(object)
        source
        
        Returns true if object is NaN.
 Note: this is not
        the same as the native isNaN function, which will also return
        true for many other not-number values, such as undefined.
      
_.isNaN(NaN); => true isNaN(undefined); => true _.isNaN(undefined); => false
        isNull_.isNull(object)
        source
        
        Returns true if the value of object is null.
      
_.isNull(null); => true _.isNull(undefined); => false
        isUndefined_.isUndefined(value)
        source
        
        Returns true if value is undefined.
      
_.isUndefined(window.missingVariable); => true
        noConflict_.noConflict()
        source
        
        Give control of the global _ variable back to its previous
        owner. Returns a reference to the Underscore object.
      
var underscore = _.noConflict();
The _.noConflict function is not present if you use the EcmaScript 6, AMD or CommonJS module system to import Underscore.
        identity_.identity(value)
        source
        
        Returns the same value that is used as the argument. In math:
        f(x) = x
        This function looks useless, but is used throughout Underscore as
        a default iteratee.
      
var stooge = {name: 'moe'};
stooge === _.identity(stooge);
=> true
      
        constant_.constant(value)
        source
        
        Creates a function that returns the same value that is used as the
        argument of _.constant.
      
var stooge = {name: 'moe'};
stooge === _.constant(stooge)();
=> true
      
        noop_.noop()
        source
        
        Returns undefined irrespective of the arguments passed to it.
        Useful as the default for optional callback arguments.
      
obj.initialize = _.noop;
        times_.times(n, iteratee, [context])
        source
        
        Invokes the given iteratee function n times. Each invocation of
        iteratee is called with an index argument.
        Produces an array of the returned values.
      
_.times(3, function(n){ genie.grantWishNumber(n); });
      
        random_.random(min, max)
        source
        
        Returns a random integer between min and max, inclusive.
        If you only pass one argument, it will return a number between 0
        and that number.
      
_.random(0, 100); => 42
        mixin_.mixin(object)
        source
        
        Allows you to extend Underscore with your own utility functions. Pass
        a hash of {name: function} definitions to have your functions
        added to the Underscore object, as well as the OOP wrapper. Returns the
        Underscore object to facilitate chaining.
_.mixin({
  capitalize: function(string) {
    return string.charAt(0).toUpperCase() + string.substring(1).toLowerCase();
  }
});
_("fabio").capitalize();
=> "Fabio"
      
        iteratee_.iteratee(value, [context])
        source
        
        Generates a callback that can be applied to each element in
        a collection. _.iteratee supports a number of shorthand
        syntaxes for common callback use cases. Depending upon value's
        type, _.iteratee will return:
      
// No value
_.iteratee();
=> _.identity()
// Function
_.iteratee(function(n) { return n * 2; });
=> function(n) { return n * 2; }
// Object
_.iteratee({firstName: 'Chelsea'});
=> _.matcher({firstName: 'Chelsea'});
// Anything else
_.iteratee('firstName');
=> _.property('firstName');
      The following Underscore methods transform their predicates through _.iteratee: countBy, every, filter, find, findIndex, findKey, findLastIndex, groupBy, indexBy, map, mapObject, max, min, partition, reject, some, sortBy, sortedIndex, and uniq
You may overwrite _.iteratee with your own custom function, if you want additional or different shorthand syntaxes:
// Support `RegExp` predicate shorthand.
var builtinIteratee = _.iteratee;
_.iteratee = function(value, context) {
  if (_.isRegExp(value)) return function(obj) { return value.test(obj) };
  return builtinIteratee(value, context);
};
      
        uniqueId_.uniqueId([prefix])
        source
        
        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.
      
_.uniqueId('contact_');
=> 'contact_104'
      
        escape_.escape(string)
        source
        
        Escapes a string for insertion into HTML, replacing
        &, <, >, ", `, and ' characters.
      
_.escape('Curly, Larry & Moe');
=> "Curly, Larry & Moe"
      
        unescape_.unescape(string)
        source
        
        The opposite of escape, replaces
        &, <, >,
        ", ` and '
        with their unescaped counterparts.
      
_.unescape('Curly, Larry & Moe');
=> "Curly, Larry & Moe"
      
        result_.result(object, property, [defaultValue])
        source
        
        If the value of the named property is a function then invoke it
        with the object as context; otherwise, return it. If a default value
        is provided and the property doesn't exist or is undefined then the default
        will be returned. If defaultValue is a function its result will be returned.
      
var object = {cheese: 'crumpets', stuff: function(){ return 'nonsense'; }};
_.result(object, 'cheese');
=> "crumpets"
_.result(object, 'stuff');
=> "nonsense"
_.result(object, 'meat', 'ham');
=> "ham"
      
        now_.now()
        source
        
        Returns an integer timestamp for the current time, using the fastest
        method available in the runtime. Useful for implementing timing/animation
        functions.
      
_.now(); => 1392066795351
        template_.template(templateString, [settings])
        source
        
        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 values, using
        <%= … %>, as well as execute arbitrary JavaScript code, with
        <% … %>. If you wish to interpolate a value, and have
        it be HTML-escaped, use <%- … %>. When you evaluate a
        template function, pass in a data object that has properties
        corresponding to the template's free variables. The settings argument
        should be a hash containing any _.templateSettings that should be overridden.
      
var compiled = _.template("hello: <%= name %>");
compiled({name: 'moe'});
=> "hello: moe"
var template = _.template("<b><%- value %></b>");
template({value: '<script>'});
=> "<b><script></b>"
      You can also use print from within JavaScript code. This is sometimes more convenient than using <%= ... %>.
var compiled = _.template("<% print('Hello ' + epithet); %>");
compiled({epithet: "stooge"});
=> "Hello stooge"
      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. Note that if part of your template matches more than one of these regexes, the first will be applied by the following order of priority: (1) escape, (2) interpolate, (3) evaluate. You may define or omit any combination of the three. For example, to perform Mustache.js-style templating:
_.templateSettings = {
  interpolate: /\{\{(.+?)\}\}/g
};
var template = _.template("Hello {{ name }}!");
template({name: "Mustache"});
=> "Hello Mustache!"
      By default, template places the values from your data in the local scope via the with 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.
_.template("Using 'with': <%= data.answer %>", {variable: 'data'})({answer: 'no'});
=> "Using 'with': no"
      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.
<script> JST.project = <%= _.template(jstText).source %>; </script>
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. source, source
_.map([1, 2, 3], function(n){ return n * 2; });
_([1, 2, 3]).map(function(n){ return n * 2; });
      Calling chain will cause all future method calls to return wrapped objects. When you've finished the computation, call value 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.
var lyrics = [
  {line: 1, words: "I'm a lumberjack and I'm okay"},
  {line: 2, words: "I sleep all night and I work all day"},
  {line: 3, words: "He's a lumberjack and he's okay"},
  {line: 4, words: "He sleeps all night and he works all day"}
];
_.chain(lyrics)
  .map(function(line) { return line.words.split(' '); })
  .flatten()
  .reduce(function(counts, word) {
    counts[word] = (counts[word] || 0) + 1;
    return counts;
  }, {})
  .value();
=> {lumberjack: 2, all: 4, night: 2 ... }
      In addition, the Array prototype's methods are proxied through the chained Underscore object, so you can slip a reverse or a push into your chain, and continue to modify the array.
        chain_.chain(obj)
        source
        
        Returns a wrapped object. Calling methods on this object will continue
        to return wrapped objects until value is called.
      
var stooges = [{name: 'curly', age: 25}, {name: 'moe', age: 21}, {name: 'larry', age: 23}];
var youngest = _.chain(stooges)
  .sortBy(function(stooge){ return stooge.age; })
  .map(function(stooge){ return stooge.name + ' is ' + stooge.age; })
  .first()
  .value();
=> "moe is 21"
      
        value_.chain(obj).value()
        source
        
        Extracts the value of a wrapped object.
      
_.chain([1, 2, 3]).reverse().value(); => [3, 2, 1]
Underscore.lua, a Lua port of the functions that are applicable in both languages. Includes OOP-wrapping and chaining. (source)
Dollar.swift, a Swift port of many of the Underscore.js functions and more. (source)
Underscore.m, an Objective-C port of many of the Underscore.js functions, using a syntax that encourages chaining. (source)
_.m, an alternative Objective-C port that tries to stick a little closer to the original Underscore.js API. (source)
Underscore.php, a PHP port of the functions that are applicable in both languages. Tailored for PHP 5.4 and made with data-type tolerance in mind. (source)
Underscore-perl, a Perl port of many of the Underscore.js functions, aimed at on Perl hashes and arrays. (source)
Underscore.cfc, a Coldfusion port of many of the Underscore.js functions. (source)
Underscore.string, an Underscore extension that adds functions for string-manipulation: trim, startsWith, contains, capitalize, reverse, sprintf, and more.
Underscore-java, a java port of the functions that are applicable in both languages. Includes OOP-wrapping and chaining. (source)
Ruby's Enumerable module.
Prototype.js, which provides JavaScript with collection functions in the manner closest to Ruby's Enumerable.
Oliver Steele's Functional JavaScript, which includes comprehensive higher-order function support as well as string lambdas.
Michael Aufreiter's Data.js, a data manipulation + persistence library for JavaScript.
Python's itertools.
PyToolz, a Python port that extends itertools and functools to include much of the Underscore API.
Funcy, a practical collection of functional helpers for Python, partially inspired by Underscore.
        On the use of < in Underscore
        
        Underscore functions that depend on ordering, such as
        _.sortBy and
        _.sortedIndex, use
        JavaScript’s built-in
        relational operators,
        specifically the “less than” operator <. It is
        important to understand that these operators are only meaningful for
        numbers and strings. You can throw any value to them, but JavaScript
        will convert the operands to string or number first before performing
        the actual comparison. If you pass an operand that
        cannot be meaningfully converted to string or number, it ends up being
        NaN by default. This value is unsortable.
      
Ideally, the values that you are sorting should either be all (meaningfully convertible to) strings or all (meaningfully convertible to) numbers. If this is not the case, you have two options:
        1.13.7 — July 24, 2024 — Diff — Docs
        
        1.13.6 — September 24, 2022 — Diff — Docs
        Hotfix for version 1.13.5 to remove a postinstall script from
        the package.json, which unexpectedly broke many people's builds.
      
        1.13.5 — September 23, 2022 — Diff — Docs
        
        1.13.4 — June 2, 2022 — Diff — Docs
        
        1.13.3 — April 23, 2022 — Diff — Docs
        
        1.13.2 — December 16, 2021 — Diff — Docs
        
        1.13.1 — April 15, 2021 — Diff — Docs
        
        1.13.0 — April 9, 2021 — Diff — Docs
        
        1.13.0-3 — March 31, 2021 — Diff — Docs
        
        1.13.0-2 — March 15, 2021 — Diff — Docs
        
        1.12.1 — March 15, 2021 — Diff — Docs
        
        1.13.0-1 — March 11, 2021 — Diff — Docs
        
        1.13.0-0 — March 9, 2021 — Diff — Docs
        
        1.12.0 — November 24, 2020 — Diff — Docs
        
        1.11.0 — August 28, 2020 — Diff — Docs — Article
        
        1.10.2 — March 30, 2020 — Diff — Docs
        
        1.10.1 — March 30, 2020 — Diff — Docs
        
        1.10.0 — March 30, 2020 — Diff — Docs
        
        1.9.2 — Jan 6, 2020 — Diff — Docs
        
        1.9.1 — May 31, 2018 — Diff — Docs
        
        1.9.0 — April 18, 2018 — Diff — Docs
        
_.partial.placeholder.
          _.bindAll now accepts arrays or arguments for keys.
          
        1.8.3 — April 2, 2015 — Diff — Docs
        
        1.8.2 — Feb. 22, 2015 — Diff — Docs
        
        1.8.1 — Feb. 19, 2015 — Diff — Docs
        
        1.8.0 — Feb. 19, 2015 — Diff — Docs
        
        1.7.0 — August 26, 2014 — Diff — Docs
        
        1.6.0 — February 10, 2014 — Diff — Docs
        
        1.5.2 — September 7, 2013 — Diff — Docs
        
        1.5.1 — July 8, 2013 — Diff — Docs
        
        1.5.0 — July 6, 2013 — Diff — Docs
        
        1.4.4 — January 30, 2013 — Diff — Docs
        
        1.4.3 — December 4, 2012 — Diff — Docs
        
        1.4.2 — October 6, 2012 — Diff — Docs
        
        1.4.1 — October 1, 2012 — Diff — Docs
        
        1.4.0 — September 27, 2012  — Diff — Docs
        
        1.3.3 — April 10, 2012 — Diff — Docs
        
        1.3.1 — January 23, 2012 — Diff — Docs
        
        1.3.0 — January 11, 2012 — Diff — Docs
        
        1.2.4 — January 4, 2012 — Diff — Docs
        
        1.2.3 — December 7, 2011 — Diff — Docs
        
        1.2.2 — November 14, 2011 — Diff — Docs
        
        1.2.1 — October 24, 2011 — Diff — Docs
        
        1.2.0 — October 5, 2011 — Diff — Docs
        
        1.1.7 — July 13, 2011 — Diff — Docs
        Added _.groupBy, which aggregates a collection into groups of like items.
        Added _.union and _.difference, to complement the
        (re-named) _.intersection.
        Various improvements for support of sparse arrays.
        _.toArray now returns a clone, if directly passed an array.
        _.functions now also returns the names of functions that are present
        in the prototype chain.
      
        1.1.6 — April 18, 2011 — Diff — Docs
        Added _.after, which will return a function that only runs after
        first being called a specified number of times.
        _.invoke can now take a direct function reference.
        _.every now requires an iterator function to be passed, which
        mirrors the ES5 API.
        _.extend no longer copies keys when the value is undefined.
        _.bind now errors when trying to bind an undefined value.
      
        1.1.5 — March 20, 2011 — Diff — Docs
        Added an _.defaults function, for use merging together JS objects
        representing default options.
        Added an _.once function, for manufacturing functions that should
        only ever execute a single time.
        _.bind now delegates to the native ES5 version,
        where available.
        _.keys now throws an error when used on non-Object values, as in
        ES5.
        Fixed a bug with _.keys when used over sparse arrays.
      
        1.1.4 — January 9, 2011 — Diff — Docs
        Improved compliance with ES5's Array methods when passing null
        as a value. _.wrap now correctly sets this for the
        wrapped function. _.indexOf now takes an optional flag for
        finding the insertion index in an array that is guaranteed to already
        be sorted. Avoiding the use of .callee, to allow _.isArray
        to work properly in ES5's strict mode.
      
        1.1.3 — December 1, 2010 — Diff — Docs
        In CommonJS, Underscore may now be required with just: 
        var _ = require("underscore").
        Added _.throttle and _.debounce functions.
        Removed _.breakLoop, in favor of an ES5-style un-break-able
        each implementation — this removes the try/catch, and you'll now have
        better stack traces for exceptions that are thrown within an Underscore iterator.
        Improved the isType family of functions for better interoperability
        with Internet Explorer host objects.
        _.template now correctly escapes backslashes in templates.
        Improved _.reduce compatibility with the ES5 version:
        if you don't pass an initial value, the first item in the collection is used.
        _.each no longer returns the iterated collection, for improved
        consistency with ES5's forEach.
      
        1.1.2 — October 15, 2010 — Diff — Docs
        Fixed _.contains, which was mistakenly pointing at
        _.intersect instead of _.include, like it should
        have been. Added _.unique as an alias for _.uniq.
      
        1.1.1 — October 5, 2010 — Diff — Docs
        Improved the speed of _.template, and its handling of multiline
        interpolations. Ryan Tenney contributed optimizations to many Underscore
        functions. An annotated version of the source code is now available.
      
        1.1.0 — August 18, 2010 — Diff — Docs
        The method signature of _.reduce has been changed to match
        the ES5 signature, instead of the Ruby/Prototype.js version.
        This is a backwards-incompatible change. _.template may now be
        called with no arguments, and preserves whitespace. _.contains
        is a new alias for _.include.
      
        1.0.4 — June 22, 2010 — Diff — Docs
        Andri Möll contributed the _.memoize
        function, which can be used to speed up expensive repeated computations
        by caching the results.
      
        1.0.3 — June 14, 2010 — Diff — Docs
        Patch that makes _.isEqual return false if any property
        of the compared object has a NaN value. Technically the correct
        thing to do, but of questionable semantics. Watch out for NaN comparisons.
      
        1.0.2 — March 23, 2010 — Diff — Docs
        Fixes _.isArguments in recent versions of Opera, which have
        arguments objects as real Arrays.
      
        1.0.1 — March 19, 2010 — Diff — Docs
        Bugfix for _.isEqual, when comparing two objects with the same
        number of undefined keys, but with different names.
      
        1.0.0 — March 18, 2010 — Diff — Docs
        Things have been stable for many months now, so Underscore is now
        considered to be out of beta, at 1.0. Improvements since 0.6
        include _.isBoolean, and the ability to have _.extend
        take multiple source objects.
      
        0.6.0 — February 24, 2010 — Diff — Docs
        Major release. Incorporates a number of
        Mile Frawley's refactors for
        safer duck-typing on collection functions, and cleaner internals. A new
        _.mixin method that allows you to extend Underscore with utility
        functions of your own. Added _.times, which works the same as in
        Ruby or Prototype.js. Native support for ES5's Array.isArray,
        and Object.keys.
      
        0.5.8 — January 28, 2010 — Diff — Docs
        Fixed Underscore's collection functions to work on
        NodeLists and
        HTMLCollections
        once more, thanks to
        Justin Tulloss.
      
        0.5.7 — January 20, 2010 — Diff — Docs
        A safer implementation of _.isArguments, and a
        faster _.isNumber,
thanks to
        Jed Schmidt.
      
        0.5.6 — January 18, 2010 — Diff — Docs
        Customizable delimiters for _.template, contributed by
        Noah Sloan.
      
        0.5.5 — January 9, 2010 — Diff — Docs
        Fix for a bug in MobileSafari's OOP-wrapper, with the arguments object.
      
        0.5.4 — January 5, 2010 — Diff — Docs
        Fix for multiple single quotes within a template string for
        _.template. See:
        Rick Strahl's blog post.
      
        0.5.2 — January 1, 2010 — Diff — Docs
        New implementations of isArray, isDate, isFunction,
        isNumber, isRegExp, and isString, thanks to
        a suggestion from
        Robert Kieffer.
        Instead of doing Object#toString
        comparisons, they now check for expected properties, which is less safe,
        but more than an order of magnitude faster. Most other Underscore
        functions saw minor speed improvements as a result.
        Evgeniy Dolzhenko
        contributed _.tap,
        similar to Ruby 1.9's,
        which is handy for injecting side effects (like logging) into chained calls.
      
        0.5.1 — December 9, 2009 — Diff — Docs
        Added an _.isArguments function. Lots of little safety checks
        and optimizations contributed by
        Noah Sloan and
        Andri Möll.
      
        0.5.0 — December 7, 2009 — Diff — Docs
        [API Changes] _.bindAll now takes the context object as
        its first parameter. If no method names are passed, all of the context
        object's methods are bound to it, enabling chaining and easier binding.
        _.functions now takes a single argument and returns the names
        of its Function properties. Calling _.functions(_) will get you
        the previous behavior.
        Added _.isRegExp so that isEqual can now test for RegExp equality.
        All of the "is" functions have been shrunk down into a single definition.
        Karl Guertin contributed patches.
      
        0.4.7 — December 6, 2009 — Diff — Docs
        Added isDate, isNaN, and isNull, for completeness.
        Optimizations for isEqual when checking equality between Arrays
        or Dates. _.keys is now 25%–2X faster (depending on your
        browser) which speeds up the functions that rely on it, such as _.each.
      
        0.4.6 — November 30, 2009 — Diff — Docs
        Added the range function, a port of the
        Python
        function of the same name, for generating flexibly-numbered lists
        of integers. Original patch contributed by
        Kirill Ishanov.
      
        0.4.5 — November 19, 2009 — Diff — Docs
        Added rest for Arrays and arguments objects, and aliased
        first as head, and rest as tail,
        thanks to Luke Sutton's patches.
        Added tests ensuring that all Underscore Array functions also work on
        arguments objects.
      
        0.4.4 — November 18, 2009 — Diff — Docs
        Added isString, and isNumber, for consistency. Fixed
        _.isEqual(NaN, NaN) to return true (which is debatable).
      
        0.4.3 — November 9, 2009 — Diff — Docs
        Started using the native StopIteration object in browsers that support it.
        Fixed Underscore setup for CommonJS environments.
      
        0.4.2 — November 9, 2009 — Diff — Docs
        Renamed the unwrapping function to value, for clarity.
      
        0.4.1 — November 8, 2009 — Diff — Docs
        Chained Underscore objects now support the Array prototype methods, so
        that you can perform the full range of operations on a wrapped array
        without having to break your chain. Added a breakLoop method
        to break in the middle of any Underscore iteration. Added an
        isEmpty function that works on arrays and objects.
      
        0.4.0 — November 7, 2009 — Diff — Docs
        All Underscore functions can now be called in an object-oriented style,
        like so: _([1, 2, 3]).map(...);. Original patch provided by
        Marc-André Cournoyer.
        Wrapped objects can be chained through multiple
        method invocations. A functions method
        was added, providing a sorted list of all the functions in Underscore.
      
        0.3.3 — October 31, 2009 — Diff — Docs
        Added the JavaScript 1.8 function reduceRight. Aliased it
        as foldr, and aliased reduce as foldl.
      
        0.3.2 — October 29, 2009 — Diff — Docs
        Now runs on stock Rhino
        interpreters with: load("underscore.js").
        Added identity as a utility function.
      
        0.3.1 — October 29, 2009 — Diff — Docs
        All iterators are now passed in the original collection as their third
        argument, the same as JavaScript 1.6's forEach. Iterating over
        objects is now called with (value, key, collection), for details
        see _.each.
      
        0.3.0 — October 29, 2009 — Diff — Docs
        Added Dmitry Baranovskiy's
        comprehensive optimizations, merged in
        Kris Kowal's patches to make Underscore
        CommonJS and
        Narwhal compliant.
      
        0.2.0 — October 28, 2009 — Diff — Docs
        Added compose and lastIndexOf, renamed inject to
        reduce, added aliases for inject, filter,
        every, some, and forEach.
      
        0.1.1 — October 28, 2009 — Diff — Docs
        Added noConflict, so that the "Underscore" object can be assigned to
        other variables.
      
        0.1.0 — October 28, 2009 — Docs
        Initial release of Underscore.js.