重读《JavaScript设计模式》－ 接口

注释

注释法用文档来约束代码，不是强制约束，只能靠开发人员自觉维护．

优点是不用额外代码支持，不会增大文件大小，不会影响执行速度．

缺点是无法提供检查，错误信息．

# interface Composite
#   add(child)
#   remove(child)
#   getChild(index)
#
# interface FormItem
#   save()

CompositeForm = (id, method, action)->
    # implements Composit, FormItem
    <link xmlns="http://docbook.org/ns/docbook" xlink:href="%E5%AF%8C%E6%9C%89%E8%A1%A8%E7%8E%B0%E5%8A%9B%E7%9A%84JavaScript.xml" xmlns:xlink="http://www.w3.org/1999/xlink"/>...
CompositeForm.portotype = 
    add: -> ...
    remove: -> ...
    getChild: -> ...
    save: -> ...

属性检查

该方法可以检查某个对象是否标注实现了某些接口，但是不检查是不是实现了接口定义的方法．

# interface Composite
#   add(child)
#   remove(child)
#   getChild(index)
#
# interface FormItem
#   save()

CompositeForm = (id, method, action)->
    @implementsInterfaces = [‘Composite‘,‘FormItem‘]
    ...

addForm = (formInstance)->
    if(!implements(formInstance, ‘Composite‘, ‘FormItem‘))
        throw new Error(‘Object does not implements a required interface.‘)
    ...

# add to global / window
glabol.implements = (object)->
    for i in [1...arguments.length] # interfaces
        if not arguments[i] in object.implementsInterfaces
            return false
    true

鸭式辨形

这种方法在上一个基础上检查了实现接口的所有方法是否进行了实现．并新增一个Interface类来辅助接口设计．

# interfaces
Composite = new Interface ‘Composite‘, [‘add‘,‘remove‘,‘getChild‘]
FormItem = new Interface ‘FormItem‘, [‘save‘]

# class
CompositeForm = (id,method,action)->
    ... # implements

# business code
addForm = (formInstance)->
    Interface.ensureImplements formInstance, Composite, FormItem

# Interface class
Interface = (name, method)->
    throw new Error("Interface constructor called with #{arguments.length} arguments, but expected exactly 2.") if arguments.length!=2
    
    @name = name
    @methods = []
    for method in methods
        throw new Error(‘Interface constructor expects method names to be passed in as a string.‘) if typeof method != ‘string‘
        @methods.push method
        
# static class method
Interface.ensureImplements = (object)->
    throw new Error("expected at least 2 arguments") if arguments.length<2
    
    for interface in arguments[1...arguments.length]
        throw new Error("Function Interface.ensureImplements expert argumnets two and above to be instances of Interface.") if interface.constructor != Interface
        for method in interface.methods
            if !object[method] || typeof object[method] != ‘function‘
                throw new Error "object does not implemnet the #{interface.name} interface. Method #{method} was not found."