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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即時網頁（Real-time web）
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129
並更新用戶端的 UI。在這樣的架構下，就可算是讓應用程式達到真正即時的效果。使用
者對系統所做的任何操作，都能立即讓其他相關的使用者知道。
使用者感受到的速度（Perceived Speed）
設計使用者介面（UI）時，速度是相當關鍵的環節（但卻也是常被程式設計師忽略的
一環），因為速度會對使用者的操作體驗（User eXperience，簡稱 UX）帶來極大的差
異，而且會直接影響到利潤。像下列這幾家公司，就一直持續在關注速度和利潤之間的
關聯：
Amazon
每多花 100 毫秒的載入時間，銷售額就會下降 1%（資料來源：Greg Linden，
Amazon）。
Google
每多花 500 毫秒的載入時間，搜尋人次就會下降 20%（資料來源：Marrissa Mayer，
Google）。
Yahoo!
每多花 400 毫秒的載入時間，網頁尚未載入完成就點選「回上一頁」的人數就會上
升 5 到 9%（資料來源：Nicole Sullivan，Yahoo!）。
使用者感受到的速度，就和實際速度同樣重要，因為那才是使用者會注意到的部分。就
算程式的實際速度不夠快，至少也要讓使用者感覺起來好像很快。而這正是 JavaScript
應用程式的拿手好戲—即使透過背景程式發送的請求還要等上一段時間才有回應，也不
會讓 UI 呈現無法使用的狀態。
再回到聊天室的範例。當使用者發送一則新訊息時，程式會透過 Ajax 請求，將這則訊
息傳送至伺服器。我們當然可以等到訊息千里迢迢的從用戶端傳到伺服器端之後，再將 ...
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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.