March 2012
Intermediate to advanced
244 pages
4h 42m
Chinese
Content preview from JavaScript 設計模式
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DOM 和瀏覽器的模式
195
事件委派
事件委派模式，是利用事件的傳播來減少附加到各個節點的事件監聽器總量。如果有個
div
元素裡面有十個按鈕，你可以在
div
上附加一個事件監聽器，而不是附加十個監聽器
在每一個按鈕上。
我們有個範例，有三顆按鈕放在一個
div
裡面（請見圖 8-1）。可以在 http://jspatterns.
com/book/8/click-delegate.html 看到實際運作的版本。
圖8-1 事件委派範例：這三顆按鈕在按下的時候，會將自己標籤中的數字加 1
所以我們使用下面的標記：
你只附加了一個監聽器至「click-wrap」
div
，而不是在每個按鈕都附加一個。接著你就可
以使用和前一個例子一樣的
myHandler()
函式，其中只有一個小小改變：你必須過濾掉你
不感興趣的點擊。在這個例子中，你僅需要在按鈕上的點擊，因此可以忽視所有其他在
div
上的點擊。
對
myHandl e r ( )
所做 的改 變， 是檢 查觸 發事件 的來 源元 素， 其
nodeNam e
是否 為
「button」：
事件委派的缺點，是需要多一點點程式碼來過濾掉發生在容器中，你不感興趣的物件的事
件。但提高效能和更乾淨的程式碼這些優點，明顯地超出缺點很多，所以這是一種高度推
薦的模式。
取得事件和來源的元素
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O’Reilly covers everything we've got, with content to help us build a world-class technology community, upgrade the capabilities and competencies of our teams, and improve overall team performance as well as their engagement.Julian F.
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.
I’ve been on the O’Reilly platform for more than eight years. I use a couple of learning platforms, but I'm on O'Reilly more than anybody else. When you're there, you start learning. I'm never disappointed.Amir M.
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.