Ajax學習二：異步請求

【1】http://www.ibm.com/developerworks/web/library/wa-ajaxintro2/index.html

1. web2.0? 什麼是web1.0

具備徹底不一樣的請求和響應模型的傳統web

• web1.0 不支持異步請求
  
• web2.0 支持異步請求
  

2. XMLHttpRequest屬性和方法

• open(): Sets up a new request to a server.
• send(): Sends a request to a server.
• abort(): Bails out of the current request.
• readyState: Provides the current HTML ready state.
• responseText: The text that the server sends back to respond to a request.

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static javascript： 代碼沒有放在一個方法或者函數體內，在用戶與頁面交互以前運行

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能夠將建立XMLHttpRequest的代碼放在函數裏面，可是會有問題：若是你是在用戶填入第14個文本框時執行Ajax代碼，而後回覆一個瀏覽器不支持的錯誤給用戶，會致使一個很是差的體驗，由於用戶已經在這個頁面花掉了10分鐘的時間。因此仍是建議使用static的代碼。

 

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ajax sandbox:  【2】http://www.cnblogs.com/ComeOn/archive/2008/01/30/1058942.html

AJAX中的沙箱安全模型主要指的是跨域腳本調用的問題。好比咱們存在在www.cnblogs.com中的腳本若是想訪問www.163.com 腳本是違反沙箱安全模型的。結果確定會出錯。

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http ready state

• 0: The request is uninitialized (before you've called open()).
• 1: The request is set up, but hasn't been sent (before you've called send()).
• 2: The request was sent and is being processed (you can usually get content headers from the response at this point).
• 3: The request is being processed; often some partial data is available from the response, but the server hasn't finished with its response.
• 4: The response is complete; you can get the server's response and use it.