March 2012
Intermediate to advanced
244 pages
4h 42m
Chinese
Content preview from JavaScript 設計模式
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函式
83
在前面的程式片段中，
sayHi()
內部的
this
指向
alien
。而在前一個例子中，
this
則是
指向全域物件。
如同這兩個範例所展示的，事實證明，原本我們以為的函式呼叫其實只不過是語法糖，等
同於函式的應用。[79]
請注意，除了
apply()
之外，
Function.prototype
物件還有個
call()
方法，而它仍只是
建構在
apply()
之上的語法糖。有的時候用語法糖比較好：當你的函式只接受一個參數，
你可以省下建立陣列的工作，只使用一個元素：
部分應用
現在我們了解，呼叫函式其實是用一組參數來應用函式，那麼有沒有可能只傳遞一部分的
參數，而非全部呢？這其實很像是你在手動解決一個數學函式時，通常會做的事情。
假設你有個
add()
函式，可以將兩個數字
x
和
y
相加。現在給定
x
是 5，
y
是 4，下面的
片段，展示出你可以如何一步步接近解答：
第二種方式比較高效，省下一個陣列
此片段目的在於說明
並非合法的 JavaScript
我們有這個函式
且我們知道參數
步驟 1—替換掉一個參數
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