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
177
最後一件事是建立和關閉遊戲：
觀察者模式（Observer）
Observer 模式廣泛的用在客戶端的 JavaScript 程式開發。所有的瀏覽器事件，包括
mouseover、keypress 等等都是這種模式的實例。這種模式也稱為自訂事件（custom
events），指的是你用程式所建立，而非瀏覽器所觸發的事件。此模式還有另一個名稱叫
做訂閱者/出版者（subscriber/publisher）模式。
此模式背後的 主要動機，是 促使降低耦合性 。物件不再是 去呼叫其他物件 的方法，
取而代之的是，物件可以訂閱（subscribes）其他物件的特定活動，並在發生時得到
通知。訂閱者也被稱為 observer（觀察者），被觀察的物件稱為出版者（publisher）
或是主題（subject）。當有重要的事件發生時，出版者會通知（呼叫）所有的訂閱者
（subscribers），且通常會用 event 物件的形式傳遞一份訊息。
範例 #1: 訂閱雜誌
讓我們來看一個具體的例子，以了解這個模式。假設你有一個出版社物件
paper
，其每日
發行報紙，還出版一份月刊雜誌。有個訂閱者
joe
會在每次出版的時候收到通知。
這個
paper
物件需要一個
subscribers
屬性，它是一個陣列，儲存著所有的訂閱者。訂閱
的動作其實就只是將訂閱者加入到這個陣列。當事件發生時，
paper
會逐一尋訪訂閱者清
單並通知他們。所謂通知，就是呼叫訂閱者物件的某個方法，因此訂閱者必須提供一 ...
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I wanted to learn C and C++, but it didn't click for me until I picked up an O'Reilly book. When I went on the O’Reilly platform, I was astonished to find all the books there, plus live events and sandboxes so you could play around with the technology.Addison B.
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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.