Underscore.js

Object-Oriented and Functional Styles

根据个人编程习惯，可以选用对象方式或函数方式使用Underscore。下面两行代码殊途同归，都是加倍一组数字。

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

Underscore的面向对象风格支持链式编程。在一个包装对象上调用chain，会让后续方法的调用也都返回包装对象。当计算结束是，用value方法得到最后的计算结果。下面的例子链式使用map/flatten/reduce，目的是得到每个单词在歌词中的数量。

 
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"}
];
 
_(lyrics).chain()
  .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 ... }

此外，Underscore对象代理Array原型的方法，所以也能够在链式中使用数组的reverse、push方法修改数组。

Collection Functions (Arrays or Objects)

each_.each(list, iterator, [context]) 别名: forEach
迭代list中的所有元素，按顺序用迭代器输出每个元素。如果传递了context参数，则把iterator绑定到context对象上。每次调用iterator都会传递三个参数：(element, index, list)。如果list是个JavaScript对象，iterator的参数是 (value, key, list))。存在原生的forEach方法，Underscore就委托给forEach。

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

map_.map(list, iterator, [context])
用转换函数把list中的每个值映射到一个新的数组。存在原生的map方法，就用原生map方法代替。如果list是个JavaScript对象，iterator的参数是(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
reduce方法把列表中元素归结为一个简单的数值，reduce的别名为inject and foldl。Memo是reduce函数的初始值，reduce的每一步都需要由iterator返回。

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

reduceRight_.reduceRight(list, iterator, memo, [context]) Alias: foldr
reducRight是从右侧开始组合的元素的reduce函数，如果存在JavaScript 1.8版本的reduceRight，则用其代替。Foldr在javascript中不像其它有懒计算的语言那么有用（lazy evaluation：一种求值策略，只有当表达式的值真正需要时才对表达式进行计算）。

 
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]

detect_.detect(list, iterator, [context])
遍历list，返回第一个通过iterator真值检测的元素值。如果找到匹配的元素立即返回，不会遍历整个list。

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

select_.select(list, iterator, [context]) Alias: filter
遍历list，返回包含所有通过iterator真值检测的元素值。如果存在原生filter方法，则委托给filter。

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

reject_.reject(list, iterator, [context])
返回那么没有通过iterator真值检测的元素数组，select的相反函数。

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

all_.all(list, iterator, [context]) Alias: every
如果list中的所有元素都通过iterator的真值检测就返回true。如果存在原生的every方法，则委托给every。

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

any_.any(list, [iterator], [context]) Alias: some
如果有任何一个元素通过通过 iterator 的真值检测就返回true。如果存在原生的some方法，则委托给some

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

include_.include(list, value) Alias: contains
如果list包含指定的value则返回true，使用===检测是否相等。如果list 是数组，内部使用indexOf判断。

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

invoke_.invoke(list, methodName, [*arguments])
在list的每个元素上执行methodName方法。任何传递给invoke的额外参数，invoke都会在调用methodName方法的时候传递给它。

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

pluck_.pluck(list, propertyName)
pluck是map最常使用的用例模型的版本，即萃取对象数组中某属性值，返回一个数组

 
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])
返回list中的最大值。如果传递iterator参数，iterator将作为list排序的依据。

 
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])
返回list中的最小值。如果传递iterator参数，iterator将作为list排序的依据。

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

sortBy_.sortBy(list, iterator, [context])
返回一个排序后的list。如果有iterator参数，iterator将作为list排序的依据。

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

groupBy_.groupBy(list, iterator)
把一个集合分组为多个集合，iterator为分组条件的迭代器

 
_.groupBy([1.3, 2.1, 2.4], function(num){ return Math.floor(num); });
=> {1: [1.3], 2: [2.1, 2.4]}

sortedIndex_.sortedIndex(list, value, [iterator])
使用二分查找确定value在list中的位置序号，value按此序号插入能保持list原有的排序。如果传递iterator参数，iterator将作为list排序的依据 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.

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

toArray_.toArray(list)
把list(任何可以迭代的对象)转换成一个Array，有助于arguments对象的转换。

 
(function(){ return _.toArray(arguments).slice(0); })(1, 2, 3);
=> [1, 2, 3]

size_.size(list)
返回list的长度。

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

Array Functions

Note: All array functions will also work on the arguments object.

first_.first(array, [n]) Alias: head
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

rest_.rest(array, [index]) Alias: tail
Returns the rest of the elements in an array. Pass an index to return the values of the array from that index onward.

 
_.rest([5, 4, 3, 2, 1]);
=> [4, 3, 2, 1]

last_.last(array)
Returns the last element of an array.

 
_.last([5, 4, 3, 2, 1]);
=> 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)
Flattens a nested array (the nesting can be to any depth).

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

without_.without(array, [*values])
Returns a copy of the array with all instances of the values removed. === is used for the equality test.

 
_.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, other)
Similar to without, but returns the values from array that are not present in other.

 
_.difference([1, 2, 3, 4, 5], [5, 2, 10]);
=> [1, 3, 4]

uniq_.uniq(array, [isSorted]) 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.

 
_.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]]

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.

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

lastIndexOf_.lastIndexOf(array, value)
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.

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

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])
把一个function绑定给一个object，任何时候调用方法，this都指向此object。随意的给函数绑定参数，预先设置这些参数，也称作currying(加脂法,怎么翻译好呢？)。

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

bindAll_.bindAll(object, [*methodNames])
把methodNames参数指定的方法绑定到对象上，这些方法就会在对象的上下文环境中执行。绑定函数用作事件处理函数时非常便利，否则函数被调用时this一点用也没有。如果不设置methodNames参数，对象上的所有方法都会被绑定。

 
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...

memoize_.memoize(function, [hashFunction])
Memoizes方法可以缓存某函数的计算结果。对于耗时较长的计算很有帮助。如果传递了hashFunction参数，就用hashFunction的返回值作为key存储函数的计算结果。 hashFunction默认使用function的第一个参数作为key

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

delay_.delay(function, wait, [*arguments])
delay类似setTimeout，等待wait毫秒后调用function。如果传递可选的参数arguments，当function执行时arguments会传递给function。

 
var log = _.bind(console.log, console);
_.delay(log, 1000, 'logged later');
=> 'logged later' // Appears after one second.

defer_.defer(function)
延迟调用function直到当前调用栈清空，类似使用延时为0的setTimeout方法。有助于执行开销大的计算和无阻塞UI线程的HTML渲染。

 
_.defer(function(){ alert('deferred'); });
// Returns from the function before the alert runs.

throttle_.throttle(function, wait)
返回一个像节流阀一样的函数，当重复调用函数的时候，最多每隔wait毫秒调用一次该函数。 对于想控制一些触发频率较高的事件有帮助。

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

debounce_.debounce(function, wait)
重复调用一个防反跳的方法，每隔wait毫秒执行一次。所谓防反跳就是setTimeout前先clearTimeout，防止新定时器开始后还执行上次的定时任务。对于必须在一些输入（多是一些用户操作）停止到达后执行的行为有帮助。例如：渲染一个减价评论的预览，window resized后计算布局。

 
var lazyLayout = _.debounce(calculateLayout, 300);
$(window).resize(lazyLayout);

once_.once(function)
创建一个只能调用一次的函数。重复调用改进的方法也没有效果，还是返回第一次执行的结果。有助于初始化类型的方法，代替过去设置一个boolean标记及后续对标记检测。

 
var initialize = _.once(createApplication);
initialize();
initialize();
// Application is only created once.

after_.after(count, function)
创建一个某生命体（函数或方法）被调用count次后才可执行的函数。当你想在一组异步请求都返回后执行一段程序时after方法非常有帮助。

 
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)
把function包装进wrapper方法，function作为第一个参数。允许wrapper在function运行前后执行代码，并且有条件的执行。

 
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)
返回一个函数列的组合物，其中每个函数消费其后跟随函数的返回值。在数学关系上，f() g()和h()函数的组合产生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]

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. It's in-order, to the last source will override properties of the same name in previous arguments.

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

defaults_.defaults(object, *defaults)
Fill in missing properties in object with default values from the defaults objects. 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.

 
_([1,2,3,200]).chain().
  select(function(num) { return num % 2 == 0; }).
  tap(console.log).
  map(function(num) { return num * num }).
  value();
=> [2, 200]
=> [4, 40000]

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

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.

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

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(variable)
Returns true if variable 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)
Invokes the given iterator function n times.

 
_(3).times(function(){ genie.grantWish(); });

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'

template_.template(templateString, [context])
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 <% … %>. When you evaluate a template function, pass in a context object that has properties corresponding to the template's free variables. If you're writing a one-off, you can pass the context object as the second parameter to template in order to render immediately instead of returning a template function.

 
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>"

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, and an (optional) evaluate regex to match expressions that should be inserted and evaluated, respectively. If no evaluate regex is provided, your templates will only be capable of interpolating values. For example, to perform Mustache.js style templating:

 
_.templateSettings = {
  interpolate : /\{\{(.+?)\}\}/g
};
 
var template = _.template("Hello {{ name }}!");
template({name : "Mustache"});
=> "Hello Mustache!"

Chaining

chain_(obj).chain()
Returns a wrapped object. Calling methods on this object will continue to return wrapped objects until value is used. ( A more realistic example.)

 
var stooges = [{name : 'curly', age : 25}, {name : 'moe', age : 21}, {name : 'larry', age : 23}];
var youngest = _(stooges).chain()
  .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]

Duck Typing

The isType (isArray, isFunction, isString ...) family of type-checking functions use property detection to do their work, which, although orders of magnitude faster than the alternative, isn't entirely safe when dealing with objects that are used as hashes, where arbitrary strings are being set for the keys. It's entirely possible for an object to masquerade as another type, if you're setting properties with names like "concat" and "charCodeAt". So be aware.

Links & Suggested Reading

Underscore.lua, a Lua port of the functions that are applicable in both languages. Includes OOP-wrapping and chaining. The source is available on GitHub.

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

1.1.7 — 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.