March 2012
Intermediate to advanced
244 pages
4h 42m
Chinese
Content preview from JavaScript 設計模式
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150
第七章
另一種解決方案，則是用立即函式包住建構式和實體。第一次呼叫建構式時會建立一個物
件，且一樣指派給 private 的
instance
。從第二次的呼叫以後，建構式只是回傳 private 變
數。對於這份實作，上面的那些測試也都能如預期運作：
工廠模式（Factory）
Factory 的目的是建立物件，它通常實作為一個 class，或者 class 的一個靜態方法。Factory
具有下列目的：
對於建立相似的物件進行重複性的運作
提供 factory 的客戶一個建立物件的方式，且無須在編譯時期知道明確的型別
（class）
確實是相同的實體
所有的原型屬性都有效
不論它們是什麼時候定義的
一般屬性可運作
建構式指標也正確
建立所有的功能
設計模式
151
第二點在以靜態 class 為基礎的語言中更為重要，因為在這類語言中，要能不事先（在編
譯時期）知道型別來建立 class 實體是很不尋常（non-trivial）的事情。而在 JavaScript，
關於這部分的實作則相當容易。
由 factory 的方法或 class 所建立的物件，會被設計成繼承同一個父物件；這些具體的
subclasses 物件則各自實作專門的功能。有時候這個公共的父親也同時是容納 fa ...
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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.