dw5ka-rqaaa-aaaad-qf7aa-cai.icp0.io Open in urlscan Pro
2a0b:21c0:4003:2:5000:55ff:feb8:5f89  Public Scan

Form analysis
0 forms found in the DOM

Text Content

Underscore.js (1.4.4)
 * » GitHub Repository
 * » Annotated Source

Introduction Collections
 * - each
 * - map
 * - reduce
 * - reduceRight
 * - find
 * - filter
 * - where
 * - findWhere
 * - reject
 * - every
 * - some
 * - contains
 * - invoke
 * - pluck
 * - max
 * - min
 * - sortBy
 * - groupBy
 * - countBy
 * - shuffle
 * - toArray
 * - size

Arrays
 * - first
 * - initial
 * - last
 * - rest
 * - compact
 * - flatten
 * - without
 * - union
 * - intersection
 * - difference
 * - uniq
 * - zip
 * - object
 * - indexOf
 * - lastIndexOf
 * - sortedIndex
 * - range

Functions
 * - bind
 * - bindAll
 * - partial
 * - memoize
 * - delay
 * - defer
 * - throttle
 * - debounce
 * - once
 * - after
 * - wrap
 * - compose

Objects
 * - keys
 * - values
 * - pairs
 * - invert
 * - functions
 * - extend
 * - pick
 * - omit
 * - defaults
 * - clone
 * - tap
 * - has
 * - isEqual
 * - isEmpty
 * - isElement
 * - isArray
 * - isObject
 * - isArguments
 * - isFunction
 * - isString
 * - isNumber
 * - isFinite
 * - isBoolean
 * - isDate
 * - isRegExp
 * - isNaN
 * - isNull
 * - isUndefined

Utility
 * - noConflict
 * - identity
 * - times
 * - random
 * - mixin
 * - uniqueId
 * - escape
 * - unescape
 * - result
 * - template

Chaining
 * - chain
 * - value

Links Change Log

Underscore is a utility-belt library for JavaScript that provides a lot of the
functional programming support that you would expect in Prototype.js (or Ruby),
but without extending any of the built-in JavaScript objects. It's the tie to go
along with jQuery's tux, and Backbone.js's suspenders.

Underscore provides 80-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 Test & Benchmark Suite is included for your perusal.

You may also read through the annotated source code.

The project is hosted on GitHub. You can report bugs and discuss features on the
issues page, on Freenode in the #documentcloud channel, or send tweets to
@documentcloud.

Underscore is an open-source component of DocumentCloud.


DOWNLOADS (RIGHT-CLICK, AND USE "SAVE AS")

Development Version (1.4.4) 40kb, Uncompressed with Plentiful Comments
Production Version (1.4.4) 4kb, Minified and Gzipped

Edge Version Unreleased, current master, use at your own risk


COLLECTION FUNCTIONS (ARRAYS OR OBJECTS)

each_.each(list, iterator, [context]) 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: (element, index, list). If list is a
JavaScript object, iterator's arguments will be (value, key, list). Delegates to
the native forEach function if it exists.

_.each([1, 2, 3], alert);
=> alerts each number in turn...
_.each({one : 1, two : 2, three : 3}, alert);
=> alerts each number value in turn...

map_.map(list, iterator, [context]) 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
(value, key, 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]

reduce_.reduce(list, iterator, memo, [context]) 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. The iterator is passed four arguments: the
memo, then the value and index (or key) of the iteration, and finally a
reference to the entire list.

var sum = _.reduce([1, 2, 3], function(memo, num){ return memo + num; }, 0);
=> 6


reduceRight_.reduceRight(list, iterator, memo, [context]) 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.

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, iterator, [context]) 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.

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


filter_.filter(list, iterator, [context]) 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.

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


where_.where(list, properties)
Looks through each value in the list, returning an array of all the values that
contain all of 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}]


findWhere_.findWhere(list, properties)
Looks through the list and returns the first value that matches all of the
key-value pairs listed in properties.

_.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."}


reject_.reject(list, iterator, [context])
Returns the values in list without the elements that the truth test (iterator)
passes. The opposite of filter.

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


every_.every(list, iterator, [context]) Alias: all
Returns true if all of the values in the list pass the iterator truth test.
Delegates to the native method every, if present.

_.every([true, 1, null, 'yes'], _.identity);
=> false


some_.some(list, [iterator], [context]) Alias: any
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.

_.some([null, 0, 'yes', false]);
=> true


contains_.contains(list, value) Alias: include
Returns true if the value is present in the list. Uses indexOf internally, if
list is an Array.

_.contains([1, 2, 3], 3);
=> true


invoke_.invoke(list, methodName, [*arguments])
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)
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, [iterator], [context])
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.

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, [iterator], [context])
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.

var numbers = [10, 5, 100, 2, 1000];
_.min(numbers);
=> 2


sortBy_.sortBy(list, iterator, [context])
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. length).

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


groupBy_.groupBy(list, iterator, [context])
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.

_.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"]}


countBy_.countBy(list, iterator, [context])
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)
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]


toArray_.toArray(list)
Converts the list (anything that can be iterated over), into a real Array.
Useful for transmuting the arguments object.

(function(){ return _.toArray(arguments).slice(1); })(1, 2, 3, 4);
=> [2, 3, 4]


size_.size(list)
Return the number of values in the list.

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



ARRAY FUNCTIONS

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]) Alias: head, take
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])
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])
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]) Alias: tail, drop
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]


compact_.compact(array)
Returns a copy of the array 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]


flatten_.flatten(array, [shallow])
Flattens a nested array (the nesting can be to any depth). If you pass shallow,
the array will only be flattened a single level.

_.flatten([1, [2], [3, [[4]]]]);
=> [1, 2, 3, 4];

_.flatten([1, [2], [3, [[4]]]], true);
=> [1, 2, 3, [[4]]];


without_.without(array, [*values])
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)
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)
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)
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], [iterator]) 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.

_.uniq([1, 2, 1, 3, 1, 4]);
=> [1, 2, 3, 4]


zip_.zip(*arrays)
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.

_.zip(['moe', 'larry', 'curly'], [30, 40, 50], [true, false, false]);
=> [["moe", 30, true], ["larry", 40, false], ["curly", 50, false]]


object_.object(list, [values])
Converts arrays into objects. Pass either a single list of [key, value] pairs,
or a list of keys, and a list of values.

_.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}


indexOf_.indexOf(array, value, [isSorted])
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 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.

_.indexOf([1, 2, 3], 2);
=> 1


lastIndexOf_.lastIndexOf(array, value, [fromIndex])
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. Pass fromIndex
to start your search at a given index.

_.lastIndexOf([1, 2, 3, 1, 2, 3], 2);
=> 4


sortedIndex_.sortedIndex(list, value, [iterator], [context])
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,
including the value you pass.

_.sortedIndex([10, 20, 30, 40, 50], 35);
=> 3


range_.range([start], stop, [step])
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. Returns a list of
integers from start to stop, incremented (or decremented) by step, exclusive.

_.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);
=> []



FUNCTION (UH, AHEM) FUNCTIONS

bind_.bind(function, object, [*arguments])
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.

var func = function(greeting){ return greeting + ': ' + this.name };
func = _.bind(func, {name : 'moe'}, 'hi');
func();
=> 'hi: moe'


bindAll_.bindAll(object, [*methodNames])
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.

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...


partial_.partial(function, [*arguments])
Partially apply a function by filling in any number of its arguments, without
changing its dynamic this value. A close cousin of bind.

var add = function(a, b) { return a + b; };
add5 = _.partial(add, 5);
add5(10);
=> 15


memoize_.memoize(function, [hashFunction])
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.

var fibonacci = _.memoize(function(n) {
  return n < 2 ? n : fibonacci(n - 1) + fibonacci(n - 2);
});


delay_.delay(function, wait, [*arguments])
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])
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)
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.

var throttled = _.throttle(updatePosition, 100);
$(window).scroll(throttled);


debounce_.debounce(function, wait, [immediate])
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 true for the immediate parameter 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);


once_.once(function)
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)
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.

var renderNotes = _.after(notes.length, render);
_.each(notes, function(note) {
  note.asyncSave({success: renderNotes});
});
// renderNotes is run once, after all notes have saved.


wrap_.wrap(function, wrapper)
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'


compose_.compose(*functions)
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 + "!"; };
var welcome = _.compose(exclaim, greet);
welcome('moe');
=> 'hi: moe!'



OBJECT FUNCTIONS

keys_.keys(object)
Retrieve all the names of the object's properties.

_.keys({one : 1, two : 2, three : 3});
=> ["one", "two", "three"]


values_.values(object)
Return all of the values of the object's properties.

_.values({one : 1, two : 2, three : 3});
=> [1, 2, 3]


pairs_.pairs(object)
Convert an object into a list of [key, value] pairs.

_.pairs({one: 1, two: 2, three: 3});
=> [["one", 1], ["two", 2], ["three", 3]]


invert_.invert(object)
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"};


functions_.functions(object) 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.

_.functions(_);
=> ["all", "any", "bind", "bindAll", "clone", "compact", "compose" ...


extend_.extend(destination, *sources)
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.

_.extend({name : 'moe'}, {age : 50});
=> {name : 'moe', age : 50}


pick_.pick(object, *keys)
Return a copy of the object, filtered to only have values for the whitelisted
keys (or array of valid keys).

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


omit_.omit(object, *keys)
Return a copy of the object, filtered to omit the blacklisted keys (or array of
keys).

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


defaults_.defaults(object, *defaults)
Fill in null and undefined properties in object with values from the defaults
objects, and return the object. As soon as the property is filled, further
defaults will have no effect.

var iceCream = {flavor : "chocolate"};
_.defaults(iceCream, {flavor : "vanilla", sprinkles : "lots"});
=> {flavor : "chocolate", sprinkles : "lots"}


clone_.clone(object)
Create a shallow-copied clone of the object. Any nested objects or arrays will
be copied by reference, not duplicated.

_.clone({name : 'moe'});
=> {name : 'moe'};


tap_.tap(object, interceptor)
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]


has_.has(object, key)
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


isEqual_.isEqual(object, other)
Performs an optimized deep comparison between the two objects, to determine if
they should be considered equal.

var moe   = {name : 'moe', luckyNumbers : [13, 27, 34]};
var clone = {name : 'moe', luckyNumbers : [13, 27, 34]};
moe == clone;
=> false
_.isEqual(moe, clone);
=> true


isEmpty_.isEmpty(object)
Returns true if object contains no values.

_.isEmpty([1, 2, 3]);
=> false
_.isEmpty({});
=> true


isElement_.isElement(object)
Returns true if object is a DOM element.

_.isElement(jQuery('body')[0]);
=> true


isArray_.isArray(object)
Returns true if object is an Array.

(function(){ return _.isArray(arguments); })();
=> false
_.isArray([1,2,3]);
=> true


isObject_.isObject(value)
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)
Returns true if object is an Arguments object.

(function(){ return _.isArguments(arguments); })(1, 2, 3);
=> true
_.isArguments([1,2,3]);
=> false


isFunction_.isFunction(object)
Returns true if object is a Function.

_.isFunction(alert);
=> true


isString_.isString(object)
Returns true if object is a String.

_.isString("moe");
=> true


isNumber_.isNumber(object)
Returns true if object is a Number (including NaN).

_.isNumber(8.4 * 5);
=> true


isFinite_.isFinite(object)
Returns true if object is a finite Number.

_.isFinite(-101);
=> true

_.isFinite(-Infinity);
=> false


isBoolean_.isBoolean(object)
Returns true if object is either true or false.

_.isBoolean(null);
=> false


isDate_.isDate(object)
Returns true if object is a Date.

_.isDate(new Date());
=> true


isRegExp_.isRegExp(object)
Returns true if object is a RegExp.

_.isRegExp(/moe/);
=> true


isNaN_.isNaN(object)
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.

_.isNaN(NaN);
=> true
isNaN(undefined);
=> true
_.isNaN(undefined);
=> false


isNull_.isNull(object)
Returns true if the value of object is null.

_.isNull(null);
=> true
_.isNull(undefined);
=> false


isUndefined_.isUndefined(value)
Returns true if value is undefined.

_.isUndefined(window.missingVariable);
=> true



UTILITY FUNCTIONS

noConflict_.noConflict()
Give control of the "_" variable back to its previous owner. Returns a reference
to the Underscore object.

var underscore = _.noConflict();

identity_.identity(value)
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
iterator.

var moe = {name : 'moe'};
moe === _.identity(moe);
=> true

times_.times(n, iterator, [context])
Invokes the given iterator function n times. Each invocation of iterator is
called with an index argument.
Note: this example uses the chaining syntax.

_(3).times(function(n){ genie.grantWishNumber(n); });

random_.random(min, max)
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)
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.

_.mixin({
  capitalize : function(string) {
    return string.charAt(0).toUpperCase() + string.substring(1).toLowerCase();
  }
});
_("fabio").capitalize();
=> "Fabio"


uniqueId_.uniqueId([prefix])
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)
Escapes a string for insertion into HTML, replacing &, <, >, ", ', and /
characters.

_.escape('Curly, Larry & Moe');
=> "Curly, Larry &amp; Moe"

unescape_.unescape(string)
The opposite of escape, replaces &amp;, &lt;, &gt;, &quot;, &#x27;, and &#x2F;
with their unescaped counterparts.

_.unescape('Curly, Larry &amp; Moe');
=> "Curly, Larry & Moe"

result_.result(object, property)
If the value of the named property is a function then invoke it; otherwise,
return it.

var object = {cheese: 'crumpets', stuff: function(){ return 'nonsense'; }};
_.result(object, 'cheese');
=> "crumpets"
_.result(object, 'stuff');
=> "nonsense"

template_.template(templateString, [data], [settings])
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 <%= … %>, 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. 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 _.templateSettings that should be overridden.

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("<b><%- value %></b>");
template({value : '<script>'});
=> "<b>&lt;script&gt;</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. 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 %>", {answer: 'no'}, {variable: 'data'});
=> "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>


CHAINING

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.

_.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, use 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)
Returns a wrapped object. Calling methods on this object will continue to return
wrapped objects until value is used.

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_(obj).value()
Extracts the value of a wrapped object.

_([1, 2, 3]).value();
=> [1, 2, 3]



LINKS & SUGGESTED READING

The Underscore documentation is also available in Simplified Chinese.

Underscore.lua, a Lua port of the functions that are applicable in both
languages. Includes OOP-wrapping and chaining. (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. Includes OOP-wrapping and chaining. (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.

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.


CHANGE LOG

1.4.4 — Jan. 30, 2013 — Diff


 * Added _.findWhere, for finding the first element in a list that matches a
   particular set of keys and values.
 * Added _.partial, for partially applying a function without changing its
   dynamic reference to this.
 * Simplified bind by removing some edge cases involving constructor functions.
   In short: don't _.bind your constructors.
 * A minor optimization to invoke.
 * Fix bug in the minified version due to the minifier incorrectly
   optimizing-away isFunction.



1.4.3 — Dec. 4, 2012 — Diff


 * Improved Underscore compatibility with Adobe's JS engine that can be used to
   script Illustrator, Photoshop, and friends.
 * Added a default _.identity iterator to countBy and groupBy.
 * The uniq function can now take array, iterator, context as the argument list.
 * The times function now returns the mapped array of iterator results.
 * Simplified and fixed bugs in throttle.



1.4.2 — Oct. 1, 2012 — Diff


 * For backwards compatibility, returned to pre-1.4.0 behavior when passing null
   to iteration functions. They now become no-ops again.



1.4.1 — Oct. 1, 2012 — Diff


 * Fixed a 1.4.0 regression in the lastIndexOf function.



1.4.0 — Sept. 27, 2012 — Diff


 * Added a pairs function, for turning a JavaScript object into [key, value]
   pairs ... as well as an object function, for converting an array of [key,
   value] pairs into an object.
 * Added a countBy function, for counting the number of objects in a list that
   match a certain criteria.
 * Added an invert function, for performing a simple inversion of the keys and
   values in an object.
 * Added a where function, for easy cases of filtering a list for objects with
   specific values.
 * Added an omit function, for filtering an object to remove certain keys.
 * Added a random function, to return a random number in a given range.
 * _.debounce'd functions now return their last updated value, just like
   _.throttle'd functions do.
 * The sortBy function now runs a stable sort algorithm.
 * Added the optional fromIndex option to indexOf and lastIndexOf.
 * "Sparse" arrays are no longer supported in Underscore iteration functions.
   Use a for loop instead (or better yet, an object).
 * The min and max functions may now be called on very large arrays.
 * Interpolation in templates now represents null and undefined as the empty
   string.
 * Underscore iteration functions no longer accept null values as a no-op
   argument. You'll get an early error instead.
 * A number of edge-cases fixes and tweaks, which you can spot in the diff.
   Depending on how you're using Underscore, 1.4.0 may be more
   backwards-incompatible than usual — please test when you upgrade.



1.3.3 — April 10, 2012


 * Many improvements to _.template, which now provides the source of the
   template function as a property, for potentially even more efficient
   pre-compilation on the server-side. You may now also set the variable option
   when creating a template, which will cause your passed-in data to be made
   available under the variable you named, instead of using a with statement —
   significantly improving the speed of rendering the template.
 * Added the pick function, which allows you to filter an object literal with a
   whitelist of allowed property names.
 * Added the result function, for convenience when working with APIs that allow
   either functions or raw properties.
 * Added the isFinite function, because sometimes knowing that a value is a
   number just ain't quite enough.
 * The sortBy function may now also be passed the string name of a property to
   use as the sort order on each object.
 * Fixed uniq to work with sparse arrays.
 * The difference function now performs a shallow flatten instead of a deep one
   when computing array differences.
 * The debounce function now takes an immediate parameter, which will cause the
   callback to fire on the leading instead of the trailing edge.



1.3.1 — Jan. 23, 2012


 * Added an _.has function, as a safer way to use hasOwnProperty.
 * Added _.collect as an alias for _.map. Smalltalkers, rejoice.
 * Reverted an old change so that _.extend will correctly copy over keys with
   undefined values again.
 * Bugfix to stop escaping slashes within interpolations in _.template.



1.3.0 — Jan. 11, 2012


 * Removed AMD (RequireJS) support from Underscore. If you'd like to use
   Underscore with RequireJS, you can load it as a normal script, wrap or patch
   your copy, or download a forked version.



1.2.4 — Jan. 4, 2012


 * You now can (and probably should, as it's simpler) write _.chain(list)
   instead of _(list).chain().
 * Fix for escaped characters in Underscore templates, and for supporting
   customizations of _.templateSettings that only define one or two of the
   required regexes.
 * Fix for passing an array as the first argument to an _.wrap'd function.
 * Improved compatibility with ClojureScript, which adds a call function to
   String.prototype.



1.2.3 — Dec. 7, 2011


 * Dynamic scope is now preserved for compiled _.template functions, so you can
   use the value of this if you like.
 * Sparse array support of _.indexOf, _.lastIndexOf.
 * Both _.reduce and _.reduceRight can now be passed an explicitly undefined
   value. (There's no reason why you'd want to do this.)



1.2.2 — Nov. 14, 2011


 * Continued tweaks to _.isEqual semantics. Now JS primitives are considered
   equivalent to their wrapped versions, and arrays are compared by their
   numeric properties only (#351).
 * _.escape no longer tries to be smart about not double-escaping
   already-escaped HTML entities. Now it just escapes regardless (#350).
 * In _.template, you may now leave semicolons out of evaluated statements if
   you wish: <% }) %> (#369).
 * _.after(callback, 0) will now trigger the callback immediately, making
   "after" easier to use with asynchronous APIs (#366).



1.2.1 — Oct. 24, 2011


 * Several important bug fixes for _.isEqual, which should now do better on
   mutated Arrays, and on non-Array objects with length properties. (#329)
 * jrburke contributed Underscore exporting for AMD module loaders, and
   tonylukasavage for Appcelerator Titanium. (#335, #338)
 * You can now _.groupBy(list, 'property') as a shortcut for grouping values by
   a particular common property.
 * _.throttle'd functions now fire immediately upon invocation, and are
   rate-limited thereafter (#170, #266).
 * Most of the _.is[Type] checks no longer ducktype.
 * The _.bind function now also works on constructors, a-la ES5 ... but you
   would never want to use _.bind on a constructor function.
 * _.clone no longer wraps non-object types in Objects.
 * _.find and _.filter are now the preferred names for _.detect and _.select.



1.2.0 — Oct. 5, 2011


 * The _.isEqual function now supports true deep equality comparisons, with
   checks for cyclic structures, thanks to Kit Cambridge.
 * Underscore templates now support HTML escaping interpolations, using <%- ...
   %> syntax.
 * Ryan Tenney contributed _.shuffle, which uses a modified Fisher-Yates to give
   you a shuffled copy of an array.
 * _.uniq can now be passed an optional iterator, to determine by what criteria
   an object should be considered unique.
 * _.last now takes an optional argument which will return the last N elements
   of the list.
 * A new _.initial function was added, as a mirror of _.rest, which returns all
   the initial values of a list (except the last N).



1.1.7 — July 13, 2011
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
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 ECMA5 API. _.extend no longer copies keys when the value is undefined.
_.bind now errors when trying to bind an undefined value.

1.1.5 — Mar 20, 2011
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
ECMAScript 5 version, where available. _.keys now throws an error when used on
non-Object values, as in ECMAScript 5. Fixed a bug with _.keys when used over
sparse arrays.

1.1.4 — Jan 9, 2011
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 — Dec 1, 2010
In CommonJS, Underscore may now be required with just:
var _ = require("underscore"). Added _.throttle and _.debounce functions.
Removed _.breakLoop, in favor of an ECMA5-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 ECMA5 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
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
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
The method signature of _.reduce has been changed to match the ECMAScript 5
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
Andri Möll contributed the _.memoize function, which can be used to speed up
expensive repeated computations by caching the results.

1.0.3
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
Fixes _.isArguments in recent versions of Opera, which have arguments objects as
real Arrays.

1.0.1
Bugfix for _.isEqual, when comparing two objects with the same number of
undefined keys, but with different names.

1.0.0
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
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
ECMAScript 5's Array.isArray, and Object.keys.

0.5.8
Fixed Underscore's collection functions to work on NodeLists and HTMLCollections
once more, thanks to Justin Tulloss.

0.5.7
A safer implementation of _.isArguments, and a faster _.isNumber,
thanks to Jed Schmidt.

0.5.6
Customizable delimiters for _.template, contributed by Noah Sloan.

0.5.5
Fix for a bug in MobileSafari's OOP-wrapper, with the arguments object.

0.5.4
Fix for multiple single quotes within a template string for _.template. See:
Rick Strahl's blog post.

0.5.2
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
Added an _.isArguments function. Lots of little safety checks and optimizations
contributed by Noah Sloan and Andri Möll.

0.5.0
[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
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
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
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
Added isString, and isNumber, for consistency. Fixed _.isEqual(NaN, NaN) to
return true (which is debatable).

0.4.3
Started using the native StopIteration object in browsers that support it. Fixed
Underscore setup for CommonJS environments.

0.4.2
Renamed the unwrapping function to value, for clarity.

0.4.1
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
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
Added the JavaScript 1.8 function reduceRight. Aliased it as foldr, and aliased
reduce as foldl.

0.3.2
Now runs on stock Rhino interpreters with: load("underscore.js"). Added identity
as a utility function.

0.3.1
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
Added Dmitry Baranovskiy's comprehensive optimizations, merged in Kris Kowal's
patches to make Underscore CommonJS and Narwhal compliant.

0.2.0
Added compose and lastIndexOf, renamed inject to reduce, added aliases for
inject, filter, every, some, and forEach.

0.1.1
Added noConflict, so that the "Underscore" object can be assigned to other
variables.

0.1.0
Initial release of Underscore.js.