假设底层Javascript引擎中存在Harmony Proxies，如何构造一个CoffeeScript父类(super class)，以便对其进行扩展将允许类定义noSuchMethod方法(或methodMessing)？
如果该类(或其父类(super class))没有请求的方法，则将使用名称和参数列表调用该方法。
最佳答案
好问题! = D
(注意:我只在Firefox中进行过测试，因为它似乎是唯一支持Harmony代理的浏览器。)
这似乎适用于缺少属性的情况:
class DynamicObject
propertyMissingHandler =
get: (target, name) ->
if name of target
target[name]
else
target.propertyMissing name
constructor: ->
return new Proxy @, propertyMissingHandler
# By default return undefined like a normal JS object.
propertyMissing: -> undefined
class Repeater extends DynamicObject
exited: no
propertyMissing: (name) ->
if @exited then "#{name.toUpperCase()}!" else name
r = new Repeater
console.log r.hi # -> hi
console.log r.exited # -> false. Doesn't print "exited" ;)
r.exited = yes
console.log r.omg # -> OMG!
现在，它可以工作，但是它有一个小的大警告:它依赖于“其他类型的”构造函数。也就是说，DynamicObject的构造函数返回的不是DynamicObject实例(它返回包装该实例的代理)。其他类型化的构造函数存在细微和不太细微的问题和they are not a very loved feature in the CoffeeScript community。
例如，上面的方法有效(在CoffeeScript 1.4中)，但这仅是因为为Repeater生成的构造函数返回了调用 super 构造函数的结果(并因此返回了代理对象)。如果Repeater具有其他构造函数，则将无法正常工作:
class Repeater extends DynamicObject
# Innocent looking constructor.
constructor: (exited = no) ->
@exited = exited
propertyMissing: (name) ->
if @exited then "#{name.toUpperCase()}!" else name
console.log (new Repeater yes).hello # -> undefined :(
您必须显式返回调用 super 构造函数的结果才能使其工作:
constructor: (exited = no) ->
@exited = exited
return super
因此，由于其他类型的构造函数有点令人困惑/损坏，我建议避免使用它们，并使用类方法实例化这些对象，而不是
new:class DynamicObject
propertyMissingHandler =
get: (target, name) ->
if name of target
target[name]
else
target.propertyMissing name
# Use create instead of 'new'.
@create = (args...) ->
instance = new @ args...
new Proxy instance, propertyMissingHandler
# By default return undefined like a normal JS object.
propertyMissing: -> undefined
class Repeater extends DynamicObject
constructor: (exited = no) ->
@exited = exited
# No need to worry about 'return'
propertyMissing: (name) ->
if @exited then "#{name.toUpperCase()}!" else name
console.log (Repeater.create yes).hello # -> HELLO!
现在，对于缺少的方法，为了与问题中请求的接口(interface)具有相同的接口(interface)，我们可以在代理处理程序中执行类似的操作，但是当目标没有属性时，无需在目标上直接调用特殊方法(propertyMissing)使用该名称，它将返回一个函数，该函数依次调用特殊方法(methodMissing):
class DynamicObject2
methodMissingHandler =
get: (target, name) ->
return target[name] if name of target
(args...) ->
target.methodMissing name, args
# Use this instead of 'new'.
@create = (args...) ->
instance = new @ args...
new Proxy instance, methodMissingHandler
# By default behave somewhat similar to normal missing method calls.
methodMissing: (name) -> throw new TypeError "#{name} is not a function"
class CommandLine extends DynamicObject2
cd: (path) ->
# Usually 'cd' is not a program on its own.
console.log "Changing path to #{path}" # TODO implement me
methodMissing: (name, args) ->
command = "#{name} #{args.join ' '}"
console.log "Executing command '#{command}'"
cl = CommandLine.create()
cl.cd '/home/bob/coffee-example' # -> Changing path to /home/bob/coffee-example
cl.coffee '-wc', 'example.coffee' # -> Executing command 'coffee -wc example.coffee'
cl.rm '-rf', '*.js' # -> Executing command 'rm -rf *.js'
不幸的是，我找不到在代理处理程序中将属性访问与方法调用区分开的方法，因此DynamicObject可以更智能，并相应地调用propertyMissing或methodMissing(尽管这很有意义，因为方法调用只是属性访问，然后是函数调用)。
如果必须选择并使DynamicObject尽可能灵活，则可以使用propertyMissing实现，因为子类可以选择他们想要如何实现propertyMissing的方式，并将缺少的属性作为方法来对待。从上面根据propertyMissing实现的CommandLine示例将是:
class CommandLine extends DynamicObject
cd: (path) ->
# Usually 'cd' is not a program on its own.
console.log "Changing path to #{path}" # TODO implement me
propertyMissing: (name) ->
(args...) ->
command = "#{name} #{args.join ' '}"
console.log "Executing command '#{command}'"
这样，我们现在可以混合从相同基类继承的Repeaters和CommandLines(多么有用!= P):
cl = CommandLine.create()
r = Repeater.create yes
cl.echo r['hello proxies'] # -> Executing command 'echo HELLO PROXIES!'