January 2013
Intermediate to advanced
332 pages
5h 23m
Chinese
Content preview from JAVASCRIPT網頁應用程式設計
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第四章
要在控制器裡定義任何全域變數，好讓控制器成為低耦合的程式元件。如果想做到上述
幾點，最佳方式莫過於採用接下來馬上要介紹的模組模式（module pattern）。
模組模式（Module Pattern）
模組模式，是一種用來封裝程式邏輯、避免全域命名空間受到干擾的絕佳做法。要實現
這個模式，全得靠匿名函式（anonymous function）。匿名函式可以說是 JavaScript 中最
棒的功能。模組模式的做法，是先建立一組匿名函式，然後馬上執行它。這麼一來，就
可以確保匿名函式裡面所有的程式碼都被安全的隔離開來，為應用程式的變數，提供一
個隱閉、私密的空間：
(function(){
/* ... */
})();
在執行匿名函式之前，需要先用括號「
（）
」把它包起來，否則 JavaScript 會沒辦法正確
解譯這段敘述句。
匯入全域變數（Global Import）
在模組裡定義的變數全都是區域變數，在全域命名空間裡不能存取這些區域變數。但在
模組裡能隨心所欲的存取全域變數。不過要小心，在模組裡濫用全域變數，容易讓人搞
不清楚究竟有哪些全域變數被模組使用，而且隨著模組規模日益擴大，這個問題也會隨
之益發嚴重。
此外，JavaScript 解譯器也會需要花費較長的時間解譯這些藏身於模組裡的全域變數。
因為 JavaScript 解譯器需要循著作用域鏈（scope chain）一層一層往外找。相較之下，
存取區域變數的效能會比較好。
有種開發模組的做法，能輕易的幫我們解決上述問題。只要把全域變數當做參數傳進匿 ...
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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.