March 2012
Intermediate to advanced
244 pages
4h 42m
Chinese
Content preview from JavaScript 設計模式
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設計模式
173
用 Proxy 作為快取
在這個範例中，proxy 的客戶物件（
videos
）夠聰明而不會對同一個影音資訊請求第二
遍。但事情可不會總是這樣。而 proxy 可以將之前的請求結果儲存在一個快取屬性中，藉
此更進一步保護真正的對象
http
（請見圖 7-6）。那麼如果
videos
物件再次要求同一份
影音 ID 的資訊，
proxy
可以從快取中取出資訊並省下一次網路的往返。
圖7-6 Proxy 的快取
中介者模式（Mediator）
應用程式—不論大小—都是由分開的物件所組成。這些所有的物件都需要一種方式彼此溝
通，且這方法不能損害可維護性，必須讓你可以安全的改變其中一部分，而不會把其他的
部分都搞壞。隨著應用程式的成長，你增加了越來越多物件，接著在重構的過程中，物件
被移來移去、重新整理。倘若物件認識太多其他的物件，又直接和這些物件溝通（例如
呼叫其他物件的方法或改變其屬性），就會導致我們所不希望看到的，緊密的耦合（tight
coupling）。當物件緊密耦合時，要改變一個物件而不影響其他就會變得困難。接著就會
演變成，甚至在應用程式中最簡單的改變，也會變得一點都不單純，於是幾乎不可能在改
變前推估應該花費的時間。[167]
Mediator 模式可以減輕這種惡劣的情況，促使降低耦合性（loose coupling），並幫助提
升可維護性。以圖 7-7 的範例來說，此模式可
以讓各個獨立物件（指 colleagues）不直接
相互溝通，而是透過一個 mediator 物件
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I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.