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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JavaScriptMVC 函式庫
|
239
型別轉換（Type Conversion）
不知你是否有注意到，伺服器回傳的
createdAt
會是像
1303173531164
這樣的數字？
這組數字其實代表的是 2011 年 4 月 18 日。對我們而言，透過
task.createdAt
拿到這
樣的一組數字其實並沒有多大意義，如果能用
new Date(1303173531164)
，將它轉換成
JavaScript 的 Date 物件，會比較有意義一些。要進行這樣的轉換，一種做法是直接寫在
設值函式
setCreatedAt
裡，但是如果有很多屬性值都需要轉換成日期格式，那模型裡面
很快就會充斥著許多重複的程式碼。
如果想讓事情變得更單純，可以利用
$.Model
來定義屬性的資料型態和轉換函式
（converter function）。做法是先在靜態物件
attributes
裡設定屬性的資料型態，然後
在靜態物件
convert
裡設定轉換函式：
$.Model('Task',{
attributes : {
createdAt : 'date'
},
convert : {
date : function(date){
return typeof date == 'number' ? new Date(date) : date;
}
}
},{});
這麼一來，
Task
就會把
createdAt
轉換為
Date
物件。如果想要列出每筆 task 的建立年
分，可以這麼寫：
Task.findAll({}, function(tasks){ ...
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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.