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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48
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第三章
利用 Ajax 載入資料
相信當你聽到「背景發出請求」時，第一個浮現在腦海中的做法，應該就是利用 Ajax
來載入遠端資料。原因很簡單：這是一種經過許多程式設計師反覆測試驗證後確認可行
的做法，而且所有目前主流的瀏覽器都支援這種做法。但並不是說 Ajax 就沒有任何缺
點—由於它過去是一項未經標準化的技術，導致今日我們所見到的 Ajax API 並不一致；
此外，如果需要載入其他網域的網站資料，會因為瀏覽器的安全性限制，造成一些較難
處理的狀況。
如果想先學習一些有關 Ajax 和
XMLHttpRequest
類別的基礎概念，建議可以拜讀
Mozilla Developer 網站上的一篇文章「Getting Started」（
https://developer.mozilla.org/
en/Ajax/Getting_Started
）。由於大多數人應該都會採用一些已經把 Ajax API 抽象化的
函式庫（像是 jQuery），來處理跨瀏覽器的相容性問題。因此，本書不會再特別介紹
XMLHttpRequest
類別，會直接說明 jQuery 的 API。
jQuery 的 Ajax API，除了提供較底層的函式
jQuery.ajax()
以外，還會在它之上提供一
層更抽象化的程式介面，讓需要撰寫的程式碼變得更少。呼叫
jQuery.ajax()
函式時，
需要傳入一堆請求相關的參數設定，像是文件類型（content type）、回叫函式…等等。
呼叫這個函式之後，程式就會在背景發出非同步的請求。
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