【第三方类库】Underscore.js Version (1.2.3) 中文文档

Underscore.js Version (1.2.3) 中文文档

Underscore 一个非常实用的JavaScript库，提供许多编程功能的支持，就像你期望 Prototype.js (或者 Ruby), 有这些功能且不扩展任何JavaScript的原生对象。 It's the tie to go along with jQuery's tux.

Underscore提供60多个方法，即有普通的功能，例如: map, select, invoke — 也有更多特殊的编程辅助方法，例如：函数绑定、javascript模板、绝对相等判断等待。 如果一些现代的浏览器提供了内置的 forEach, map, reduce, filter, every, some 和 indexOf方法，Underscore就委托给浏览器原生的方法。

Underscore提供完整的测试用例集供你精读。

你也可以阅读有注释的源代码。

项目代码放在GitHub上，你可以通过issues页、Freenode的#documentcloud频道、发送tweets给@documentcloud三个途径报告bug以及参与特性讨论。

Underscore是DocumentCloud的一个开源组件。

下载 (Right-click, and use "Save As")

Development Version (1.2.3)	34kb, Uncompressed with Comments
Production Version (1.2.3)	< 4kb, Minified and Gzipped

Table of Contents

Object-Oriented and Functional Styles（面向对象和函数风格）

Collections（收集）
each, map, reduce, reduceRight, find, filter, reject, all, any, include, invoke, pluck, max, min, sortBy, groupBy, sortedIndex, shuffle, toArray, size

Arrays（数组）
first, initial, last, rest, compact, flatten, without, union, intersection, difference, uniq, zip, indexOf, lastIndexOf, range

Functions（函数）
bind, bindAll, memoize, delay, defer, throttle, debounce, once, after, wrap, compose

Objects（对象）
keys, values, functions, extend, defaults, clone, tap, isEqual, isEmpty, isElement, isArray, isArguments, isFunction, isString, isNumber, isBoolean, isDate, isRegExp, isNaN, isNull, isUndefined

Utility（功能）
noConflict, identity, times, mixin, uniqueId, escape, template

Chaining
chain, value

Object-Oriented and Functional Styles

根据自己的喜好，您可以使用下划线在一个面向对象或函数风格，下面的两行代码相同的效果，都是一组数字乘2。

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

使用面向对象的风格允许您链式调用多个方法。在一个包装对象上调用调用chain，会导致后续所有的方法调用同时返回包装对象。使用value方法得到检索的最终值。这里有一个链式使用map/flatten/reduce的例子，为了获得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 ... }

另外，Array原型的方法通过链式代理Underscore对象， ，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]) Alias: forEach
遍历list中的所有元素，按顺序用遍历输出每个元素。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的别名为inject 和 foldl。reduce方法把列表中元素归结为一个简单的数值。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]

find_.find(list, iterator, [context]) Alias: detect
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 = _.find([1, 2, 3, 4, 5, 6], function(num){ return num % 2 == 0; });
=> 2

filter_.filter(list, iterator, [context]) Alias: select
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 = _.filter([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]}
_.groupBy(['one', 'two', 'three'], 'length');
=> {3: ["one", "two"], 5: ["three"]}

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

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

shuffle_.shuffle(list)
返回 list 的序的副本，使用 Fisher-Yates shuffle版本

_.shuffle([1, 2, 3, 4, 5, 6]);
=> [4, 1, 6, 3, 5, 2]

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

注： arguments（参数） 对象将在所有数组函数中工作 。
Note: All array functions will also work on the arguments object.

first_.first(array, [n]) Alias: head
返回array（数组）的第一个元素。传递 n参数将返回数组中从第一个元素开始的n个元素。

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

initial_.initial(array, [n])
返回数组中除了最后一个元素外的其他全部元素。尤其用于参数对象。传递 n参数将从结果中排除从最后一个开始的n个元素。

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

last_.last(array, [n])
返回array（数组）的最后一个元素。传递 n参数将返回数组中从最后一个元素开始的n个元素。

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

rest_.rest(array, [index]) Alias: tail
返回数组中除了第一个元素外的其他全部元素。传递 index参数将返回数组中从index开始的新数组。

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

compact_.compact(array)
返回一个删除所有false值的 array副本。 在javascript中, false, null, 0, "", undefined 和 NaN 都是false值.

_.compact([0, 1, false, 2, '', 3]);
=> [1, 2, 3]

flatten_.flatten(array)
返回一个单嵌套的array（数组）（嵌套可以是任何深度）。

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

without_.without(array, [*values])
返回一个删除所有实例值的 array副本。使用===表达式做相等测试。

_.without([1, 2, 1, 0, 3, 1, 4], 0, 1);
=> [2, 3, 4]

union_.union(*arrays)
计算传入的 arrays（数组）并集：按顺序返回一个存在于一个或多个 arrays（数组）中独一无二的项目列表。

_.union([1, 2, 3], [101, 2, 1, 10], [2, 1]);
=> [1, 2, 3, 101, 10]

intersection_.intersection(*arrays)
计算传入的 arrays（数组）交集。结果中的每个值是存在于传入的每个arrays（数组）。

_.intersection([1, 2, 3], [101, 2, 1, 10], [2, 1]);
=> [1, 2]

difference_.difference(array, *others)
类似于without，但从返回的值来自array参数数组，不存在于other 数组.

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

uniq_.uniq(array, [isSorted], [iterator]) Alias: unique
数组去重，生成无重复的array版本，使用===表达式做相等测试。如果您事先知道该 array 进行已经排序，传递true给isSorted将会更快的算法运行，如果您要计算转变类型的唯一项，可以传递一个iterator 函数。 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)
将 每个相应位置的arrays的值合并在一起。当你有单独的有用数据源时通过匹配数组索引协调。如果您正在使用嵌套的数组矩阵，zip.apply可以转置矩阵相似的方式。
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])
返回value在该 array 中的索引值，如果value不存在 array中就返回-1。使用原生的indexOf 函数，除非它失效。如果您正在使用一个大数组，你知道数组已经排序，传递true给isSorted将更快的用二进制搜索

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

lastIndexOf_.lastIndexOf(array, value)
返回value在该 array 中的从最后开始的索引值，如果value不存在 array中就返回-1。如果支持原生的lastIndexOf，将使用原生的lastIndexOf函数。

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

range_.range([start], stop, [step])
一个用来创建整数灵活编号的列表的函数，便于each 和 map循环。如果省略start则默认为 0；step 默认为 1.返回一个从start 到stop的整数的列表，用step来增加 （或减少）独占。

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

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)
检索object的所有的属性名称。

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

values_.values(object)
返回 object所有的属性的值。

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

functions_.functions(object) Alias: methods
返回对象中的每个方法的名称排序列表 —即是说,每个对象的属性函数的名称。

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

extend_.extend(destination, *sources)
复制source对象中的所有属性覆盖到destination对象上，他是按照循序的，所以最后源将重写在前面参数相同名称的属性。

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

defaults_.defaults(object, *defaults)
用defaults 对象中属性填充object中缺少的属性的默认值。尽快填充属性，进一步的默认值将没有任何效果。

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

clone_.clone(object)
创建 一个浅复制（浅拷贝）的克隆object。任何嵌套的对象或数组都通过引用拷贝，不会复制。

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

tap_.tap(object, interceptor)
用 object调用interceptor，然后返回object。这种方法的主要目的是"进入"方法链，为了对中间结果链内执行操作。

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

isEqual_.isEqual(object, other)
执行两个对象之间的优化深度比较，确定他们是否应被视为相等。

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)
如果object 不包含值，返回true

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

isElement_.isElement(object)
如果object是一个DOM元素，返回true

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

isArray_.isArray(object)
如果object是一个数组，返回true

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

isArguments_.isArguments(object)
如果object是一个参数对象，返回true

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

isFunction_.isFunction(object)
如果object是一个函数，返回true

_.isFunction(alert);
=> true

isString_.isString(object)
如果object是一个字符串，返回true

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

isNumber_.isNumber(object)
如果object是一个数值，返回true

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

isBoolean_.isBoolean(object)
如果object是一个布尔值，返回true

_.isBoolean(null);
=> false

isDate_.isDate(object)
如果object是一个日期时间，返回true

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

isRegExp_.isRegExp(object)
如果object是一个正则表达式，返回true

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

isNaN_.isNaN(object)
如果object是 NaN，返回true。
注意： 这和原生的isNaN 函数不一样，如果变量是undefined，原生的isNaN 函数也会返回 true。

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

isNull_.isNull(object)
如果object的值是 null，返回true。

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

isUndefined_.isUndefined(variable)
如果variable是undefined，返回true。

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

Utility Functions

noConflict_.noConflict()
放弃Underscore 的控制变量"_"。返回Underscore 对象的引用。

var underscore = _.noConflict();

identity_.identity(value)
返回用作参数的相同值。数学 f(x) = x
此函数查找无用，但使用整个Underscore作为默认的迭代器。

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

times_.times(n, iterator)
调用给定的迭代函数n次

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

mixin_.mixin(object)
您可以用您自己的实用程序函数扩展Underscore。传递一个 {name: function}定义的哈希添加到Underscore对象，以及面向对象包装。

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

uniqueId_.uniqueId([prefix])
为需要的客户端模型或DOM元素生成一个全局唯一的id。如果prefix参数存在， id 将附加给它

_.uniqueId('contact_');
=> 'contact_104'

escape_.escape(string)
转义HTML字符串，替换&, <, >, ", ', and /字符

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

template_.template(templateString, [context])
将 JavaScript 模板编译为可以计算用于呈现的函数。 HTML 的复杂的结构用JSON数据源用呈现。模板函数可以是以下两种内部变量：使用<%= … %>，以及用<% … %>执行任意 JavaScript 代码。如果您想插入一个值，它将 HTML 转义，当你使用<%- … %> 评估模板函数，在传递有对应于该模板的属性变量context。如果你在写一次过，你可以传递context作为 template 的第二个参数，以便立即呈现而不是返回的模板函数。
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 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>"
var template = _.template("<b><%- value %></b>");
template({value : '<script>'});
=> "<b>&lt;script&gt;</b>"

您还可以使用 JavaScript 代码内print 。这是有时比使用<%= ... %>更方便 .

var compiled = _.template("<% print('Hello ' + epithet); %>");
compiled({epithet: "stooge"});
=> "Hello stooge."

If ERB-style delimiters aren't your cup of tea, 您可以更改下划线的模板设置，使用不同的符号来表示插值的代码。定义 interpolate 正则表达式，和 （可选）evaluate正则表达式来匹配，但是必须分别是inserted 和 evaluated,如果不提供evaluate正则表达式，您的模板将只能够的插补值。 例如, 看看 Mustache.js 样式模板:

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

Chaining

chain_(obj).chain()
返回一个对象被包装的对象。对象上调用方法将继续以返回被包装的对象，直到 value被使用。 (一个更现实的例子)

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()
提取被包装的对象的值。

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

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

Underscore-perl, a Perl port of many of the Underscore.js functions, aimed at on Perl hashes and arrays, also 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

1.2.3 — 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.