CoffeeScript 可编译成 JavaScript 的脚本语言中文文档

Question

CoffeeScript 是一门编译到 JavaScript 的小巧语言，在 Java 般笨拙的外表下, JavaScript 其实有着一颗华丽的心脏，CoffeeScript 尝试用简洁的方式展示 JavaScript 优秀的部分。

CoffeeScript 的指导原则是 "她仅仅是 JavaScript"，代码一一对应地编译到 JS, 不会在编译过程中进行解释。

已有的 JavaScript 类库可以无缝地和 CoffeeScript 搭配使用，反之亦然，编译后的代码是可读的, 且经过美化, 能在所有 JavaScript 环境中运行，并且应该和对应手写的 JavaScript 一样快或者更快。

最新版本：1.7.1

sudo npm install -g coffee-script

概览

左边是 CoffeeScript 右边是编译后输出的 JavaScript.

# 赋值:
number   = 42
opposite = true

# 条件:
number = -42 if opposite

# 函数:
square = (x) -> x * x

# 数组:
list = [1, 2, 3, 4, 5]

# 对象:
math =
root:   Math.sqrt
square: square
cube:   (x) -> x * square x

# Splats:
race = (winner, runners...) ->
print winner, runners

# 存在性:
alert "I knew it!" if elvis?

# 数组 推导(comprehensions):
cubes = (math.cube num for num in list)

var cubes, list, math, num, number, opposite, race, square,
__slice = [].slice;

number = 42;

opposite = true;

if (opposite) {
number = -42;
}

square = function(x) {
return x * x;
};

list = [1, 2, 3, 4, 5];

math = {
root: Math.sqrt,
square: square,
cube: function(x) {
  return x * square(x);
}
};

race = function() {
var runners, winner;
winner = arguments[0], runners = 2 <= arguments.length ? __slice.call(arguments, 1) : [];
return print(winner, runners);
};

if (typeof elvis !== "undefined" && elvis !== null) {
alert("I knew it!");
}

cubes = (function() {
var _i, _len, _results;
_results = [];
for (_i = 0, _len = list.length; _i < _len; _i++) {
  num = list[_i];
  _results.push(math.cube(num));
}
return _results;
})();

安装

CoffeeScript 编译器本身是 CoffeeScript 写的，使用了 Jison parser generator。

命令行版本的 coffee 是一个实用的 Node.js 工具，不过编译器并不依赖 Node，而是能运行于任何 JavaScript 执行环境，比如说在浏览器里。

安装前你需要最新稳定版 Node.js，和 npm (Node Package Manager)，借助 npm 可以安装 CoffeeScript：

npm install -g coffee-script

如果不想全局安装可以去掉 -g 选项，如果你希望安装 master 分支上最新的 CoffeeScript，你可以从源码仓库 克隆 CoffeeScript，或直接下载源码，还有通过 npm 方式安装 master 分支最新的 CoffeeScript 编译器：

npm install -g http://github.com/jashkenas/coffee-script/tarball/master

或者你想将其安装到 /usr/local, 而不用 npm 进行管理，进入 coffee-script 目录执行：

sudo bin/cake install

用法

安装之后, 你应该可以运行 coffee 命令以执行脚本，编译 .coffee 文件到 .js 文件，和提供一个交互式的 REPL，coffee 命令有下列参数:

-c, --compile	编译一个 .coffee 脚本到一个同名的 .js 文件.
-m, --map	随 JavaScript 文件一起生成 source maps. 并且在 JavaScript 里加上 sourceMappingURL 指令.
-i, --interactive	启动一个交互式的 CoffeeScript 会话用来尝试一些代码片段. 等同于执行 coffee 而不加参数.
-o, --output [DIR]	将所有编译后的 JavaScript 文件写到指定文件夹. 与 --compile 或 --watch 搭配使用.
-j, --join [FILE]	编译之前, 按参数传入顺序连接所有脚本到一起, 编译后写到指定的文件. 对于编译大型项目有用.
-w, --watch	监视文件改变, 任何文件更新时重新执行命令.
-p, --print	JavaScript 直接打印到 stdout 而不是写到一个文件.
-s, --stdio	将 CoffeeScript 传递到 STDIN 后从 STDOUT 获取 JavaScript. 对其他语言写的进程有好处. 比如: cat src/cake.coffee | coffee -sc
-l, --literate	将代码作为 Literate CoffeeScript 解析. 只会在从 stdio 直接传入代码或者处理某些没有后缀的文件名需要写明这点.
-e, --eval	直接从命令行编译和打印一小段 CoffeeScript. 比如: coffee -e "console.log num for num in [10..1]"
-b, --bare	编译到 JavaScript 时去掉顶层函数的包裹.
-t, --tokens	不对 CoffeeScript 进行解析, 仅仅进行 lex, 打印出 token stream: [IDENTIFIER square] [ASSIGN =] [PARAM_START (] ...
-n, --nodes	不对 CoffeeScript 进行编译, 仅仅 lex 和解析, 打印 parse tree:

Expressions
Assign
  Value "square"
  Code "x"
    Op *
      Value "x"
      Value "x"

--nodejsnode 命令有一些实用的参数，比如--debug, --debug-brk, --max-stack-size和 --expose-gc。用这个参数直接把参数转发到 Node.js。重复使用 --nodejs 来传递多个参数。

例子:

• 编译一个 .coffee 文件的树形目录 src 到一个同级 js 文件树形目录 lib：
  coffee --compile --output lib/ src/
• 监视一个文件的改变, 每次文件被保证时重新编译：
  coffee --watch --compile experimental.coffee
• 合并一组文件到单个脚本：
  coffee --join project.js --compile src/*.coffee
• 从一个 one-liner 打印编译后的 JS：
  coffee -bpe "alert i for i in [0..10]"
• 现在全部一起, 在你工作时监视和重复编译整个项目：
  coffee -o lib/ -cw src/
• 运行 CoffeeScript REPL (Ctrl-D 来终止, Ctrl-V 激活多行)：
  coffee

Literate CoffeeScript

除了被作为一个普通的编程语言，CoffeeScript 也可以在 "literate" 模式下编写。如果你以 .litcoffee 为扩展名命名你的文件，你可以把它当作 Markdown 文件来编写，此文档恰好也是一份可执行的 CoffeeScript 代码，编译器将会把所有的缩进块 (Markdown 表示源代码的方式) 视为代码，其他部分则为注释。

Just for kicks, a little bit of the compiler is currently implemented in this fashion，See it as a document, raw, and properly highlighted in a text editor.

I'm fairly excited about this direction for the language, and am looking forward to writing (and more importantly, reading) more programs in this style.
More information about Literate CoffeeScript, including an example program, are available in this blog post.

语言手册

这份手册所设计的结构，方便从上往下进行阅读。后边的章节使用前面介绍的语法和手法。阅读这份手册需要对 JavaScript 比较熟悉。以下所有的例子, CoffeeScript 源码将在左边显示, 并在右侧直接编译到 JavaScript。

首先, 一些基础, CoffeeScript 使用显式的空白来区分代码块.你不需要使用分号 ; 来关闭表达式,在一行的结尾换行就可以了(尽管分号依然可以用来把多行的表达式简写到一行里).不需要再用花括号来{ } 包裹代码快, 在 函数,if 表达式,switch, 和 try/catch 当中使用缩进.

传入参数的时候, 你不需要再使用圆括号来表明函数被执行.隐式的函数调用的作用范围一直到行尾或者一个块级表达式.

console.log sys.inspect object → console.log(sys.inspect(object));

函数

函数通过一组可选的圆括号包裹的参数, 一个箭头, 一个函数体来定义.一个空的函数像是这样:

square = (x) -> x * x
cube   = (x) -> square(x) * x

var cube, square;

square = function(x) {
return x * x;
};

cube = function(x) {
return square(x) * x;
};

一些函数函数参数会有默认值, 当传入的参数的不存在 (null 或者 undefined)时会被使用.

fill = (container, liquid = "coffee") ->
"Filling the #{container} with #{liquid}..."

var fill;

fill = function(container, liquid) {
if (liquid == null) {
  liquid = "coffee";
}
return "Filling the " + container + " with " + liquid + "...";
};

对象和数组

CoffeeScript 中对象和数组的字面量看起来很像在 JavaScript 中的写法.如果单个属性被写在自己的一行里, 那么逗号是可以省略的.和 YAML 类似, 对象可以用缩进替代花括号来声明.

song = ["do", "re", "mi", "fa", "so"]

singers = {Jagger: "Rock", Elvis: "Roll"}

bitlist = [
1, 0, 1
0, 0, 1
1, 1, 0
]

kids =
brother:
  name: "Max"
  age:  11
sister:
  name: "Ida"
  age:  9

var bitlist, kids, singers, song;

song = ["do", "re", "mi", "fa", "so"];

singers = {
Jagger: "Rock",
Elvis: "Roll"
};

bitlist = [1, 0, 1, 0, 0, 1, 1, 1, 0];

kids = {
brother: {
  name: "Max",
  age: 11
},
sister: {
  name: "Ida",
  age: 9
}
};

JavaScript 里, 你不能使用不添加引号的保留字段作为属性名称, 比如 class.CoffeeScript 里作为键出现的保留字会被识别并补上引号,所以你不用有额外的操心(比如说, 使用 jQuery 的时候).

$('.account').attr class: 'active'

log object.class

$('.account').attr({
"class": 'active'
});

log(object["class"]);

词法作用域和变量安全

CoffeeScript 编译器会考虑所有变量, 保证每个变量都在词法域里适当地被定义，你永远不需要自己去写 var.

outer = 1
changeNumbers = ->
inner = -1
outer = 10
inner = changeNumbers()

var changeNumbers, inner, outer;

outer = 1;

changeNumbers = function() {
var inner;
inner = -1;
return outer = 10;
};

inner = changeNumbers();

注意所有变量的定义都被推到相关的顶层作用域, 也就是第一次出现的位置.outer 在内层的函数里没有被重新定义, 因为它已经存在于作用域当中了.同时, 内层函数里的 inner 不应该改变外部的同名的变量, 所以在这里有自己的声明.

其行为和 Ruby 的局部变量的作用域实际上是一致的.由于你没有对 var 关键字的直接访问, 根据需要隐藏一个外部变量就很容易, 你只能引用它.所以在写深层的嵌套的函数时, 注意不要意外用到和外部变量相同的名字.

尽管要说清楚会受到文档长度限制, 函数的所有 CoffeeScript 结果都被一个匿名函数包裹：

(function(){ ... })();

这层安全的封装, 加上自动生成的 var 关键字, 使得不小心污染全局命名空间很难发生.

如果你希望创建一个其他脚本也能使用的顶层变量, 那么将其作为赋值在 window 上,或者在 CommonJS 里的 exports 上.存在操作符(existential operator)可以帮你写出一个可靠的方式找到添加位置;比如你的目标是同时满足 CommonJS 和浏览器: exports ? this

if, else, unless 和条件赋值

if/else 表达式可以不用圆括号和花括号就写出来.就像函数和其他块级表达式那样, 多行的条件可以通过缩进来表明.另外还有一个顺手的后缀形式, 在行尾使用 if or unless.

CoffeeScript 会尝试编译 if 语句到 JavaScript 表达式, 或者一个封装的闭包.CoffeeScript 里不存在直白的三元表达式.— 你只要在一行内使用普通的 if 语句.

mood = greatlyImproved if singing

if happy and knowsIt
clapsHands()
chaChaCha()
else
showIt()

date = if friday then sue else jill

var date, mood;

if (singing) {
mood = greatlyImproved;
}

if (happy && knowsIt) {
clapsHands();
chaChaCha();
} else {
showIt();
}

date = friday ? sue : jill;

变参(splats)...

使用 JavaScript 的 arguments 对象是一种处理接收不定数量个参数的函数常用办法.CoffeeScript 在函数定义和调用里提供了变参(splats) ... 的语法,让不定个数的参数使用起来更愉悦一些.

gold = silver = rest = "unknown"

awardMedals = (first, second, others...) ->
gold   = first
silver = second
rest   = others

contenders = [
"Michael Phelps"
"Liu Xiang"
"Yao Ming"
"Allyson Felix"
"Shawn Johnson"
"Roman Sebrle"
"Guo Jingjing"
"Tyson Gay"
"Asafa Powell"
"Usain Bolt"
]

awardMedals contenders...

alert "Gold: " + gold
alert "Silver: " + silver
alert "The Field: " + rest

var awardMedals, contenders, gold, rest, silver,
__slice = [].slice;

gold = silver = rest = "unknown";

awardMedals = function() {
var first, others, second;
first = arguments[0], second = arguments[1], others = 3 <= arguments.length ? __slice.call(arguments, 2) : [];
gold = first;
silver = second;
return rest = others;
};

contenders = ["Michael Phelps", "Liu Xiang", "Yao Ming", "Allyson Felix", "Shawn Johnson", "Roman Sebrle", "Guo Jingjing", "Tyson Gay", "Asafa Powell", "Usain Bolt"];

awardMedals.apply(null, contenders);

alert("Gold: " + gold);

alert("Silver: " + silver);

alert("The Field: " + rest);

循环和推导式

你可以使用CoffeeScript将大多数的循环写成基于数组、对象或范围的推导式(comprehensions)。推导式替代（编译为）for循环，并且可以使用可选的子句和数组索引值。不同于for循环，数组的推导式是表达式，可以被返回和赋值。

# 吃午饭.
eat food for food in ['toast', 'cheese', 'wine']

# 精致的五道菜.
courses = ['greens', 'caviar', 'truffles', 'roast', 'cake']
menu i + 1, dish for dish, i in courses

# 注重健康的一餐.
foods = ['broccoli', 'spinach', 'chocolate']
eat food for food in foods when food isnt 'chocolate'

var courses, dish, food, foods, i, _i, _j, _k, _len, _len1, _len2, _ref;

_ref = ['toast', 'cheese', 'wine'];
for (_i = 0, _len = _ref.length; _i < _len; _i++) {
food = _ref[_i];
eat(food);
}

courses = ['greens', 'caviar', 'truffles', 'roast', 'cake'];

for (i = _j = 0, _len1 = courses.length; _j < _len1; i = ++_j) {
dish = courses[i];
menu(i + 1, dish);
}

foods = ['broccoli', 'spinach', 'chocolate'];

for (_k = 0, _len2 = foods.length; _k < _len2; _k++) {
food = foods[_k];
if (food !== 'chocolate') {
  eat(food);
}
}

推导式可以适用于其他一些使用循环的地方，例如each/forEach,map，或者select/filter，例如：

shortNames = (name for name in list when name.length < 5)

如果你知道循环的开始与结束，或者希望以固定的跨度迭代，你可以在范围推导式中指定开始与结束。

countdown = (num for num in [10..1])

var countdown, num;

countdown = (function() {
var _i, _results;
_results = [];
for (num = _i = 10; _i >= 1; num = --_i) {
  _results.push(num);
}
return _results;
})();

注意：上面的例子中我们展示了如何将推导式赋值给变量，CoffeeScript总是将每个循环项收集到一个数组中。但是有时候以循环结尾的函数运行的目的就是它们的副作用(side-effects)。这种情况下要注意不要意外的返回推导式的结果，而是在函数的结尾增加一些有意义的返回值—例如 true 或 null。

在推导式中使用by子句，可以实现以固定跨度迭代范围值：

evens = (x for x in [0..10] by 2)

推导式也可以用于迭代对象中的key和value。在推导式中使用of来取出对象中的属性，而不是数组中的值。

yearsOld = max: 10, ida: 9, tim: 11

ages = for child, age of yearsOld
"#{child} is #{age}"

var age, ages, child, yearsOld;

yearsOld = {
max: 10,
ida: 9,
tim: 11
};

ages = (function() {
var _results;
_results = [];
for (child in yearsOld) {
  age = yearsOld[child];
  _results.push("" + child + " is " + age);
}
return _results;
})();

如果你希望仅迭代在当前对象中定义的属性，通过hasOwnProperty检查并避免属性是继承来的，可以这样来写：

for own key, value of object

CoffeeScript仅提供了一种底层循环，即while循环。与JavaScript中的while循环的主要区别是，在CoffeeScript中while可以作为表达式来使用，而且可以返回一个数组，该数组包含每个迭代项的迭代结果。

# 经济 101
if this.studyingEconomics
buy()  while supply > demand
sell() until supply > demand

# 摇篮曲
num = 6
lyrics = while num -= 1
"#{num} little monkeys, jumping on the bed.
  One fell out and bumped his head."

var lyrics, num;

if (this.studyingEconomics) {
while (supply > demand) {
  buy();
}
while (!(supply > demand)) {
  sell();
}
}

num = 6;

lyrics = (function() {
var _results;
_results = [];
while (num -= 1) {
  _results.push("" + num + " little monkeys, jumping on the bed. One fell out and bumped his head.");
}
return _results;
})();

为了更好的可读性，until关键字等同于while not, loop关键字等同于while true。

使用 JavaScript 循环生成函数的时候, 经常会添加一个闭包来包裹代码,这样做目的是为了循环的变量被保存起来, 而不是所有生成的函数搜去访问最后一个循环的变量.CoffeeScript 提供了一个 do 关键字, 用来直接调用跟在后边的函数, 并且传递需要的参数.

for filename in list
do (filename) ->
  fs.readFile filename, (err, contents) ->
    compile filename, contents.toString()

var filename, _fn, _i, _len;

_fn = function(filename) {
return fs.readFile(filename, function(err, contents) {
  return compile(filename, contents.toString());
});
};
for (_i = 0, _len = list.length; _i < _len; _i++) {
filename = list[_i];
_fn(filename);
}

数组的切片和用 range 进行拼接

Range 也可以被用来展开数组的切片.

• 通过两个点号的写法 (3..6), range 会包含最后一个数据 (3, 4, 5, 6);
• 通过三个点号的写法 (3...6), range 不会包含最后一个数据 (3, 4, 5).

切片的索引位置存在不错的默认值. 前面的索引位置省略的话, 默认会是 0,后面的索引位置被省略的话, 默认值是数组的大小.

numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9]

start   = numbers[0..2]

middle  = numbers[3...-2]

end     = numbers[-2..]

copy    = numbers[..]

var copy, end, middle, numbers, start;

numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9];

start = numbers.slice(0, 3);

middle = numbers.slice(3, -2);

end = numbers.slice(-2);

copy = numbers.slice(0);

同样的语法还可以用在数组的片段上赋值一些新的值, 进行拼接.

numbers = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

numbers[3..6] = [-3, -4, -5, -6]

var numbers, _ref;

numbers = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9];

[].splice.apply(numbers, [3, 4].concat(_ref = [-3, -4, -5, -6])), _ref;

注意 JavaScript 的 string 是不可变的, 所以不能用被拼接.

一切都是表达式 (至少尽可能成为)

读者大概有注意到上面的代码 CoffeeScript 函数是不需要写 return 语句的, 但是也会返回最终的结果.CoffeeScript 编译器会尽可能保证语言中所有的表达式都可以被当作表达式使用.观察一下下面的函数, return 是怎样尽可能地插入到执行的分支当中的.

grade = (student) ->
if student.excellentWork
  "A+"
else if student.okayStuff
  if student.triedHard then "B" else "B-"
else
  "C"

eldest = if 24 > 21 then "Liz" else "Ike"

var eldest, grade;

grade = function(student) {
if (student.excellentWork) {
  return "A+";
} else if (student.okayStuff) {
  if (student.triedHard) {
    return "B";
  } else {
    return "B-";
  }
} else {
  return "C";
}
};

eldest = 24 > 21 ? "Liz" : "Ike";

尽管函数总是会自动 return 其最终的值, 你可以在函数体前面显式地写上 (return value),这个做法也是值得借鉴的, 前提是你明确你在做的事情是什么.

由于变量声明是生成在作用域顶部, 所以在表达式内部也可以写赋值, 即便是前面没写到过的变量.

six = (one = 1) + (two = 2) + (three = 3)

var one, six, three, two;

six = (one = 1) + (two = 2) + (three = 3);

有些代码在 JavaScript 当中要写不少的语句, 而在 CoffeeScript 中只是表达式的一部分,这些代码的编译结果会自动生成一个闭包. 这个写法很有用, 比如把列表解析的结果赋值给变量:

# 前十个全局属性(变量).

globals = (name for name of window)[0...10]

var globals, name;

globals = ((function() {
var _results;
_results = [];
for (name in window) {
  _results.push(name);
}
return _results;
})()).slice(0, 10);

结果是一些原来明确是语句的东西也可以像, 比如把 try/catch 语句直接传给函数调用:

alert(
try
  nonexistent / undefined
catch error
  "And the error is ... #{error}"
)

var error;

alert((function() {
try {
  return nonexistent / void 0;
} catch (_error) {
  error = _error;
  return "And the error is ... " + error;
}
})());

有一些 JavaScript 语句是不能编译到表达式的对应的语义的, 比如 break, continue 和 return.如果你的代码当中用到了它们, CoffeeScript 是不会尝试去进行转换的.

操作符和 aliase

由于操作符 == 常常带来不准确的约束, 不容易达到效果, 而且跟其他语言当中意思不一致,CoffeeScript 会把 == 编译为 ===, 把 != 变异为 !==.
此外, is 编译为 ===, 而 isnt 编译为 !==.

not 可以作为 ! 的 alias 使用.

逻辑操作方面, and 编译为 &&, 而 or 编译为 ||.

在 while, if/else, switch/when 的语句当中,then 可以被用来分隔判断条件跟表达式, 这样就不用强制写换行或者分号了.

就像 YAML, on 和 yes跟 true 是一样的, 而 off 和 no 是布尔值 false.

unless 可以认为是 if 相反的版本.

this.property 简短的写法可以用 @property.

可以用 in 判断数据在数组中是否出现, 而 of可以探测 JavaScript 对象的属性是否存在.

为了简化数学表达式, ** 可以用来表示乘方, // 表示整除, %%提供数学的模运算(译注: true mathematical modulo?).

完整的列表:

CoffeeScript	JavaScript
is	===
isnt	!==
not	!
and	&&
or	||
true, yes, on	true
false, no, off	false
@, this	this
of	in
in	no JS equivalent
a ** b	Math.pow(a, b)
a // b	Math.floor(a / b)
a %% b	(a % b + b) % b

launch() if ignition is on

volume = 10 if band isnt SpinalTap

letTheWildRumpusBegin() unless answer is no

if car.speed < limit then accelerate()

winner = yes if pick in [47, 92, 13]

print inspect "My name is #{@name}"

var volume, winner;

if (ignition === true) {
launch();
}

if (band !== SpinalTap) {
volume = 10;
}

if (answer !== false) {
letTheWildRumpusBegin();
}

if (car.speed < limit) {
accelerate();
}

if (pick === 47 || pick === 92 || pick === 13) {
winner = true;
}

print(inspect("My name is " + this.name));

存在性操作符

在 JavaScript 里检测一个变量的存在性有点麻烦.if (variable) ... 比较接近答案, 但是对 `0` 不成立.CoffeeScript 的存在性操作符 ? 除非是 null 或者 undefined, 否则都返回 true,这大致是模仿 Ruby 当中的 nil?.

这也可以用在比 ||= 更安全的条件赋值当中, 有些情况你会需要处理数字跟字符串的.

solipsism = true if mind? and not world?

speed = 0
speed ?= 15

footprints = yeti ? "bear"

var footprints, solipsism, speed;

if ((typeof mind !== "undefined" && mind !== null) && (typeof world === "undefined" || world === null)) {
solipsism = true;
}

speed = 0;

if (speed == null) {
speed = 15;
}

footprints = typeof yeti !== "undefined" && yeti !== null ? yeti : "bear";

存在性操作符 ?. 的访问器的变体可以用来吸收链式属性调用中的 null.数据可能是 null 或者 undefined 的情况下可以用这种写法替代访问器 .如果所有属性都存在, 那么你会得到想要的结果, 如果链式调用有问题, 会返回 undefined 而不是抛出 TypeError.

zip = lottery.drawWinner?().address?.zipcode

var zip, _ref;

zip = typeof lottery.drawWinner === "function" ? (_ref = lottery.drawWinner().address) != null ? _ref.zipcode : void 0 : void 0;

吸收 null 数据的做法类似 Ruby 的 andand gem, 和 Groovy 的 safe navigation operator.

class, 继承, super

JavaScript 的原型继承有点烧脑, 存在大量的类库用于在 JavaScript 的原型之上实现更清晰的 class 继承, 比如:Base2,Prototype.js,JS.Class.

这些类库提供了语法糖, 但如果不是因为一些例外的话原生的继承完全是可用的, 例外比如:很难调用 super(当前函数的原型上的实现), 很难正确设置原型链.

相比重复地设置函数的原型, CoffeeScript 提供了一个基础的 class 结构,你可以在一个定义的表达式里完成命名 class, 定义父类, 赋值原型上的属性, 定义构造器.

构造函数被命名, 这对查看调用栈有更好的支持.下面例子中的第一个类, this.constructor.name is "Animal".

class Animal
constructor: (@name) ->

move: (meters) ->
  alert @name + " moved #{meters}m."

class Snake extends Animal
move: ->
  alert "Slithering..."
  super 5

class Horse extends Animal
move: ->
  alert "Galloping..."
  super 45

sam = new Snake "Sammy the Python"
tom = new Horse "Tommy the Palomino"

sam.move()
tom.move()

var Animal, Horse, Snake, sam, tom,
__hasProp = {}.hasOwnProperty,
__extends = function(child, parent) { for (var key in parent) { if (__hasProp.call(parent, key)) child[key] = parent[key]; } function ctor() { this.constructor = child; } ctor.prototype = parent.prototype; child.prototype = new ctor(); child.__super__ = parent.prototype; return child; };

Animal = (function() {
function Animal(name) {
  this.name = name;
}

Animal.prototype.move = function(meters) {
  return alert(this.name + (" moved " + meters + "m."));
};

return Animal;

})();

Snake = (function(_super) {
__extends(Snake, _super);

function Snake() {
  return Snake.__super__.constructor.apply(this, arguments);
}

Snake.prototype.move = function() {
  alert("Slithering...");
  return Snake.__super__.move.call(this, 5);
};

return Snake;

})(Animal);

Horse = (function(_super) {
__extends(Horse, _super);

function Horse() {
  return Horse.__super__.constructor.apply(this, arguments);
}

Horse.prototype.move = function() {
  alert("Galloping...");
  return Horse.__super__.move.call(this, 45);
};

return Horse;

})(Animal);

sam = new Snake("Sammy the Python");

tom = new Horse("Tommy the Palomino");

sam.move();

tom.move();

如果你不喜欢用 class 的裁判法定义原型, CoffeeScript 提供了一些低级的方便写法.
extends 操作符可以用来恰当地定义任何一对构造函数的原型链;
用 :: 可以快速访问对象的原型;
super() 可以编译为一个父类上同名方法的调用.

String::dasherize = ->
this.replace /_/g, "-"

String.prototype.dasherize = function() {
return this.replace(/_/g, "-");
};

最后, class 定义是可执行的代码, 这样就可能进行元编程.
因为在 class 定义的上下文当中, this 是类对象本身(构造函数),可以用 @property: value 赋值静态的属性,也可以调用父类的方法: @attr 'title', type: 'text'.

解构赋值

CoffeeScript 实现 ECMAScript Harmony 的提议 解构赋值 语法, 这样从复杂的数组和对象展开数据会更方便一些.
当你把数组或者对象的字面量赋值到一个变量时, CoffeeScript 把等式两边都解开配对, 把右边的值赋值给左边的变量.
最简单的例子, 可以用来并行赋值:

theBait   = 1000
theSwitch = 0

[theBait, theSwitch] = [theSwitch, theBait]

var theBait, theSwitch, _ref;

theBait = 1000;

theSwitch = 0;

_ref = [theSwitch, theBait], theBait = _ref[0], theSwitch = _ref[1];

用来处理函数多返回值也很方便.

weatherReport = (location) ->
# 发起一个 Ajax 请求获取天气...
[location, 72, "Mostly Sunny"]

[city, temp, forecast] = weatherReport "Berkeley, CA"

var city, forecast, temp, weatherReport, _ref;

weatherReport = function(location) {
return [location, 72, "Mostly Sunny"];
};

_ref = weatherReport("Berkeley, CA"), city = _ref[0], temp = _ref[1], forecast = _ref[2];

解构赋值可以用在深度嵌套的数组跟对象上, 取出深度嵌套的属性.

futurists =
sculptor: "Umberto Boccioni"
painter:  "Vladimir Burliuk"
poet:
  name:   "F.T. Marinetti"
  address: [
    "Via Roma 42R"
    "Bellagio, Italy 22021"
  ]

{poet: {name, address: [street, city]}} = futurists

var city, futurists, name, street, _ref, _ref1;

futurists = {
sculptor: "Umberto Boccioni",
painter: "Vladimir Burliuk",
poet: {
  name: "F.T. Marinetti",
  address: ["Via Roma 42R", "Bellagio, Italy 22021"]
}
};

_ref = futurists.poet, name = _ref.name, (_ref1 = _ref.address, street = _ref1[0], city = _ref1[1]);

解构赋值还可以跟 splats 搭配使用.

tag = "<impossible>"

[open, contents..., close] = tag.split("")

var close, contents, open, tag, _i, _ref,
__slice = [].slice;

tag = "<impossible>";

_ref = tag.split(""), open = _ref[0], contents = 3 <= _ref.length ? __slice.call(_ref, 1, _i = _ref.length - 1) : (_i = 1, []), close = _ref[_i++];

展开式(expansion)可以用于获取数组结尾的元素, 而不需要对中间过程的数据进行赋值.它也可以用在函数参数的列表上.

text = "Every literary critic believes he will
      outwit history and have the last word"

[first, ..., last] = text.split " "

var first, last, text, _ref;

text = "Every literary critic believes he will outwit history and have the last word";

_ref = text.split(" "), first = _ref[0], last = _ref[_ref.length - 1];

解构赋值也可以用在 class 的构造器上, 从构造器配置对象赋值到示例属性上.

class Person
constructor: (options) -> 
  {@name, @age, @height} = options

tim = new Person age: 4

var Person, tim;

Person = (function() {
function Person(options) {
  this.name = options.name, this.age = options.age, this.height = options.height;
}

return Person;

})();

tim = new Person({
age: 4
});

函数绑定

JavaScript 当中 this 关键字被动态地设定为当前函数挂载所在的对象上.如果你把函数当作回调, 或者挂载到别的对象, 那么原先的 this 就丢失了.
如果你不了解这个行为,If you're not familiar with this behavior,this Digital Web article 对怪异模式做了很好的回顾.

Fat arrow => 可以同时定义函数, 绑定函数的 this 到当前的值, 正是我们需要的.
这有助于在 Prototype 或者 jQuery 这种基于回调的类库当中使用,用于创建迭代器函数传递给 each, 或者借助 bind 的事件处理器函数.
Fat arrow 定义的函数可以访问到他们创建位置的 this 对象的属性.

Account = (customer, cart) ->
@customer = customer
@cart = cart

$('.shopping_cart').bind 'click', (event) =>
  @customer.purchase @cart

var Account;

Account = function(customer, cart) {
this.customer = customer;
this.cart = cart;
return $('.shopping_cart').bind('click', (function(_this) {
  return function(event) {
    return _this.customer.purchase(_this.cart);
  };
})(this));
};

如果上边用的是 this,@customer 会指向一个 DOM 元素的 undefined "customer" 属性,然后强行调用上面的 purchase() 时会抛出一个异常.

对于类的定义, 实例创建的过程中 fat arrow 定义的方法会自动绑定到类的每个示例上去.

嵌入 JavaScript

这个写法应该不会被用到, 但如果什么时候需要在 CoffeeScript 中穿插 JavaScript 片段的话,你可以用反引号直接传进去.

hi = `function() {
return [document.title, "Hello JavaScript"].join(": ");
}`

var hi;

hi = function() {
return [document.title, "Hello JavaScript"].join(": ");
};

Switch/When/Else

JavaScript 里的 Switch 语句有点难看.
你需要在每个 case 写 break 防止自动进入默认的 case.
CoffeeScript 会阻止掉意外的 fall-through.
而且 switch 编译的结果会是可以带 return, 可以被用于赋值的表达式.
格式这样写: switch 判断条件,when 然后子句, else 然后默认的 case.

就像 Ruby, CoffeeScript 里边 switch 语句对于每个子句可以带多个值.
任何一个值匹配的情况下, 子句就会执行.

switch day
when "Mon" then go work
when "Tue" then go relax
when "Thu" then go iceFishing
when "Fri", "Sat"
  if day is bingoDay
    go bingo
    go dancing
when "Sun" then go church
else go work

switch (day) {
case "Mon":
  go(work);
  break;
case "Tue":
  go(relax);
  break;
case "Thu":
  go(iceFishing);
  break;
case "Fri":
case "Sat":
  if (day === bingoDay) {
    go(bingo);
    go(dancing);
  }
  break;
case "Sun":
  go(church);
  break;
default:
  go(work);
}

Switch 语句也可以不写控制条件, 当作 if/else 调用链的一个更整洁的可选写法.

score = 76
grade = switch
when score < 60 then 'F'
when score < 70 then 'D'
when score < 80 then 'C'
when score < 90 then 'B'
else 'A'
# grade == 'C'

var grade, score;

score = 76;

grade = (function() {
switch (false) {
  case !(score < 60):
    return 'F';
  case !(score < 70):
    return 'D';
  case !(score < 80):
    return 'C';
  case !(score < 90):
    return 'B';
  default:
    return 'A';
}
})();

Try/Catch/Finally

Try/catch 语句基本上 JavaScript 的一样(尽管它们是表达式执行).

try
allHellBreaksLoose()
catsAndDogsLivingTogether()
catch error
print error
finally
cleanUp()

var error;

try {
allHellBreaksLoose();
catsAndDogsLivingTogether();
} catch (_error) {
error = _error;
print(error);
} finally {
cleanUp();
}

Chained Comparisons

CoffeeScript 从 Python 学习了 链式对比 — 这样判断数值是否在某个范围内在写法上更容易.

cholesterol = 127
healthy = 200 > cholesterol > 60

var cholesterol, healthy;
cholesterol = 127;
healthy = (200 > cholesterol && cholesterol > 60);

字符串替换, 块级的字符串, 块级的注释

Ruby 风格的字符串替换也在 CoffeeScript 实现了. 双引号包裹的字符串允许数据替换, 用 #{ ... } 语法,而单引号包裹的字符串仅仅是字面量.

author = "Wittgenstein"
quote  = "A picture is a fact. -- #{ author }"

sentence = "#{ 22 / 7 } is a decent approximation of π"

var author, quote, sentence;

author = "Wittgenstein";

quote = "A picture is a fact. -- " + author;

sentence = "" + (22 / 7) + " is a decent approximation of π";

CoffeeScript 支持多行字符串.
行与行会用一个空格拼接, 除非结尾用了反斜杠.
其中缩进会被忽略.

mobyDick = "Call me Ishmael. Some years ago --
never mind how long precisely -- having little
or no money in my purse, and nothing particular
to interest me on shore, I thought I would sail
about a little and see the watery part of the
world..."

var mobyDick;

mobyDick = "Call me Ishmael. Some years ago -- never mind how long precisely -- having little or no money in my purse, and nothing particular to interest me on shore, I thought I would sail about a little and see the watery part of the world...";

块级的字符串可以用于书写格式化的或者对缩进敏感的文本(或者你只是不想转义单引号双引号).
代码块开始的位置的缩进层级会被保留, 用在后面的代码中, 所以这部分代码依然可以跟整体的代码一起对齐.

html = """
     <strong>
       cup of coffeescript
     </strong>
     """

var html;

html = "<strong>\n  cup of coffeescript\n</strong>";

块级的字符串用双引号, 跟普通的双引号字符串一样, 支持替换.

有时候你想把整块的注释传给生成的 JavaScript. 比如在文件顶部嵌入协议.
块级的注释, 仿照了块级字符串的语法, 将会在生成的代码当中保留.

###
SkinnyMochaHalfCaffScript Compiler v1.0
Released under the MIT License
###

/*
SkinnyMochaHalfCaffScript Compiler v1.0
Released under the MIT License
*/

块级的正则表达式

类似块级的字符串跟注释, CoffeeScript 支持块级的正则 —扩展了正则表达式, 可以忽略内部的空格, 可以包含注释和替换.
模仿了 Perl 的 /x 修饰符, CoffeeScript 的块级正则以 /// 为界,让正则表达式获得了很大程度的可读性. 引用一下 CoffeeScript 源码:

OPERATOR = /// ^ (
?: [-=]>             # 函数
 | [-+*/%<>&|^!?=]=  # 复合赋值 / 比较
 | >>>=?             # 补 0 右移
 | ([-+:])\1         # 双写
 | ([&|<>])\2=?      # 逻辑 / 移位
 | \?\.              # soak 访问
 | \.{2,3}           # 范围或者 splat
) ///

var OPERATOR;
OPERATOR = /^(?:[-=]>|[-+*\/%<>&|^!?=]=|>>>=?|([-+:])\1|([&|<>])\2=?|\?\.|\.{2,3})/;

Cake, and Cakefiles

CoffeeScript includes a (very) simple build system similar to Make and Rake. Naturally, it's called Cake, and is used for the tasks that build and test the CoffeeScript language itself. Tasks are defined in a file named Cakefile, and can be invoked by running cake [task] from within the directory.
To print a list of all the tasks and options, just type cake.

Task definitions are written in CoffeeScript, so you can put arbitrary code in your Cakefile. Define a task with a name, a long description, and the function to invoke when the task is run. If your task takes a command-line option, you can define the option with short and long flags, and it will be made available in the options object. Here's a task that uses the Node.js API to rebuild CoffeeScript's parser:

fs = require 'fs'

option '-o', '--output [DIR]', 'directory for compiled code'

task 'build:parser', 'rebuild the Jison parser', (options) ->
require 'jison'
code = require('./lib/grammar').parser.generate()
dir  = options.output or 'lib'
fs.writeFile "#{dir}/parser.js", code

var fs;

fs = require('fs');

option('-o', '--output [DIR]', 'directory for compiled code');

task('build:parser', 'rebuild the Jison parser', function(options) {
var code, dir;
require('jison');
code = require('./lib/grammar').parser.generate();
dir = options.output || 'lib';
return fs.writeFile("" + dir + "/parser.js", code);
});

If you need to invoke one task before another — for example, running build before test, you can use the invoke function:
invoke 'build'. Cake tasks are a minimal way to expose your CoffeeScript functions to the command line, so don't expect any fanciness built-in.
If you need dependencies, or async callbacks, it's best to put them in your code itself — not the cake task.

Source Maps

CoffeeScript 1.6.1 and above include support for generating source maps, a way to tell your JavaScript engine what part of your CoffeeScript program matches up with the code being evaluated. Browsers that support it can automatically use source maps to show your original source code in the debugger. To generate source maps alongside your JavaScript files, pass the --map or -m flag to the compiler.

For a full introduction to source maps, how they work, and how to hook them up in your browser, read the HTML5 Tutorial.

text/coffeescript Script Tags

While it's not recommended for serious use, CoffeeScripts may be included directly within the browser using <script type="text/coffeescript">
tags. The source includes a compressed and minified version of the compiler (Download current version here, 39k when gzipped) as extras/coffee-script.js. Include this file on a page with inline CoffeeScript tags, and it will compile and evaluate them in order.

In fact, the little bit of glue script that runs "Try CoffeeScript" above, as well as the jQuery for the menu, is implemented in just this way.
View source and look at the bottom of the page to see the example.
Including the script also gives you access to CoffeeScript.compile()so you can pop open Firebug and try compiling some strings.

The usual caveats about CoffeeScript apply — your inline scripts will run within a closure wrapper, so if you want to expose global variables or functions, attach them to the window object.

Books

There are a number of excellent resources to help you get started with CoffeeScript, some of which are freely available online.

• The Little Book on CoffeeScript is a brief 5-chapter introduction to CoffeeScript, written with great clarity and precision by Alex MacCaw.
• Smooth CoffeeScript is a reimagination of the excellent book Eloquent JavaScript, as if it had been written in CoffeeScript instead. Covers language features as well as the functional and object oriented programming styles. By E. Hoigaard.
• CoffeeScript: Accelerated JavaScript Development is Trevor Burnham's thorough introduction to the language. By the end of the book, you'll have built
  a fast-paced multiplayer word game, writing both the client-side and Node.js portions in CoffeeScript.
• CoffeeScript Programming with jQuery, Rails, and Node.js is a new book by Michael Erasmus that covers CoffeeScript with an eye towards real-world usage both in the browser (jQuery) and on the server size (Rails, Node).
• CoffeeScript Ristretto is a deep dive into CoffeeScript's semantics from simple functions up through closures, higher-order functions, objects, classes, combinators, and decorators. By Reg Braithwaite.
• Testing with CoffeeScript is a succinct and freely downloadable guide to building testable applications with CoffeeScript and Jasmine.
• CoffeeScript Application Development is a new book from Packt Publishing that introduces CoffeeScript while walking through the process of building a demonstration web application.
• CoffeeScript in Action is a new book from Manning Publications that covers CoffeeScript syntax, composition techniques and application development.

Screencasts

• A Sip of CoffeeScript is a Code School Course which combines 6 screencasts with in-browser coding to make learning fun. The first level is free to try out.
• Meet CoffeeScript is a 75-minute long screencast by PeepCode.
  Highly memorable for its animations which demonstrate transforming CoffeeScript into the equivalent JS.
• If you're looking for less of a time commitment, RailsCasts' CoffeeScript Basics should have you covered, hitting all of the important notes about CoffeeScript in 11 minutes.

Examples

The best list of open-source CoffeeScript examples can be found on GitHub. But just to throw out few more:

• github's Hubot,a friendly IRC robot that can perform any number of useful and useless tasks.
• sstephenson's Pow,a zero-configuration Rack server, with comprehensive annotated source.
• technoweenie's Coffee-Resque,a port of Resque for Node.js.
• assaf's Zombie.js,a headless, full-stack, faux-browser testing library for Node.js.
• jashkenas' Underscore.coffee, a port of the Underscore.js
  library of helper functions.
• stephank's Orona, a remake of the Bolo tank game for modern browsers.
• josh's nack, a Node.js-powered Rack server.

Resources

• Source Code
  Use bin/coffee to test your changes,bin/cake test to run the test suite,bin/cake build to rebuild the CoffeeScript compiler, and bin/cake build:parser to regenerate the Jison parser if you're working on the grammar.git checkout lib && bin/cake build:full is a good command to run when you're working on the core language. It'll refresh the lib directory (in case you broke something), build your altered compiler, use that to rebuild itself (a good sanity test) and then run all of the tests. If they pass, there's a good chance you've made a successful change.
• CoffeeScript Issues
  Bug reports, feature proposals, and ideas for changes to the language belong here.
• CoffeeScript Google Group
  If you'd like to ask a question, the mailing list is a good place to get help.
• The CoffeeScript Wiki
  If you've ever learned a neat CoffeeScript tip or trick, or ran into a gotcha — share it on the wiki.
  The wiki also serves as a directory of handy text editor extensions, web framework plugins, and general CoffeeScript build tools.
• The FAQ
  Perhaps your CoffeeScript-related question has been asked before. Check the FAQ first.
• JS2Coffee
  Is a very well done reverse JavaScript-to-CoffeeScript compiler. It's not going to be perfect (infer what your JavaScript classes are, when you need bound functions, and so on...) — but it's a great starting point for converting simple scripts.
• High-Rez Logo
  The CoffeeScript logo is available in Illustrator, EPS and PSD formats, for use in presentations.