Underscore.js是一个很精干的库，压缩后只有4KB。它提供了几十种函数式编程的方法，弥补了标准库的不足，大大方便了JavaScript的编程。MVC框架Backbone.js就将这个库作为自己的工具库。除了可以在浏览器环境使用，Underscore.js还可以用于Node.js。

Underscore.js定义了一个下划线（_）对象，函数库的所有方法都属于这个对象。这些方法大致上可以分成：集合（collection）、数组（array）、函数（function）、对象（object）和工具（utility）五大类。

nderscore is a JavaScript library that provides a whole mess of 一大堆useful functional programming helpers without extending any built-in objects. It’s the answer to the question: “If I sit down in front of a blank HTML page, and want to start being productive immediately, what do I need?” … and the tie to go along with jQuery‘s tux andBackbone‘s suspenders.

Underscore provides 80-odd 80左右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.

Underscore提供的60多个函数：

http://www.css88.com/doc/underscore/

 部分函数：

Collections（集合） 
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

Collection Functions (Arrays or Objects)

英文：

中文翻译：http://www.css88.com/doc/underscore/

each_.each(list, iterator, [context]) Alias: forEach 
Iterates over a list of elements, yielding each in turn to an iterator function. Theiterator 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 forEachfunction if it exists, and returns the original list for chaining.

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

Note: Collection functions work on arrays, objects, and array-like objects such asarguments, NodeList and similar. But it works by duck-typing, so avoid passing objects with a numeric length property. It‘s also good to note that an each loop cannot be broken out of — to break, use _.find instead.

map_.map(list, iterator, [context]) Alias: collect 
通过变换函数（iterator迭代器）把list中的每个值映射到一个新的数组中（愚人码头注：产生一个新的数组）。如果存在原生的map方法，就用原生map方法来代替。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 
别名为 inject 和 foldl, reduce方法把list中元素归结为一个单独的数值。Memo是reduce函数的初始值，reduce的每一步都需要由iterator返回。这个迭代传递4个参数：memo, value 和 迭代的index（或者 key）和最后一个引用的整个 list。

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迭代器真值检测的元素值，如果没有值传递给测试迭代器将返回undefined。 如果找到匹配的元素，函数将立即返回，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中的每个值，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，则用原生的filter方法。

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

where_.where(list, properties) 
遍历list中的每一个值，返回一个数组，这个数组包含包含properties所列出的属性的所有的键 - 值对。

_.where(listOfPlays, {author: "Shakespeare", year: 1611});
=> [{title: "Cymbeline", author: "Shakespeare", year: 1611},
    {title: "The Tempest", author: "Shakespeare", year: 1611}]

findWhere_.findWhere(list, properties) 
遍历list中的每一个值，返回匹配properties所列出的属性的所有的键 - 值对的第一个值。

如果没有找到匹配的属性，或者list是空的，那么将返回undefined。

_.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]) 
返回list中没有通过iterator真值检测的元素集合，与filter相反。

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

toArray方法将对象转为数组，只包含对象成员的值。典型应用是将对类似数组的对象转为真正的数组。

 _.toArray({a:0,b:1,c:2});
// [0, 1, 2]

pluck方法将多个对象的某一个属性的值，提取成一个数组。

var stooges = [{name : ‘moe‘, age : 40}, {name : ‘larry‘, age : 50}, {name : ‘curly‘, age : 60}];

_.pluck(stooges, ‘name‘);
// ["moe", "larry", "curly"]

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

var buttonView = {
  label  : ‘underscore‘,
  onClick: function(){ alert(‘clicked: ‘ + this.label); },
  onHover: function(){ console.log(‘hovering: ‘ + this.label); }
};
_.bindAll(buttonView, ‘onClick‘, ‘onHover‘);
// When the button is clicked, this.label will have the correct value.
jQuery(‘#underscore_button‘).bind(‘click‘, buttonView.onClick);

var o = {
    p: 2,
    m: function (){console.log(this.p);}
};

o.m()
// 2

_.bind(o.m,{p:1})()
// 1

var add = function(n1,n2,n3) {
  console.log(this.sum + n1 + n2 + n3);
};

_.bind(add, {sum:1}, 1, 1, 1)()
// 4

var o = {
  p1 : ‘123‘,
  p2 : ‘456‘,
  m1 : function() { console.log(this.p1); },
  m2 : function() { console.log(this.p2); },
};

_.bindAll(o, ‘m1‘, ‘m2‘);

var add = function(a, b) { return a + b; };

add5 = _.partial(add, 5);

add5(10);
// 15

var hello = function(name) { return "hello: " + name; };

hello = _.wrap(hello, function(func) {
  return "before, " + func("moe") + ", after";
});

hello();
// ‘before, hello: moe, after‘

var greet    = function(name){ return "hi: " + name; };
var exclaim  = function(statement){ return statement + "!"; };
var welcome = _.compose(exclaim, greet);
welcome(‘moe‘);
// ‘hi: moe!‘

underscore.js框架使用,布布扣,bubuko.com

underscore.js框架使用