Ajax 核心框架函数及例子

// A generic function for performming AJAX requests 
// It takes one argument, which is an object that contains a set of options 
// All of which are outline in the comments, below 
function ajax( options ) { 
// Load the options object with defaults, if no 
// values were provided by the user 
options = { 
// The type of HTTP Request 
type: options.type || "POST", 
// The URL the request will be made to 
url: options.url || "", 
// How long to wait before considering the request to be a timeout 
timeout: options.timeout || 5000, 
// Functions to call when the request fails, succeeds, 
// or completes (either fail or succeed) 
onComplete: options.onComplete || function(){}, 
onError: options.onError || function(){}, 
onSuccess: options.onSuccess || function(){}, 
// The data type that'll be returned from the server 
// the default is simply to determine what data was returned from the 
// and act accordingly. 
data: options.data || "" 
}; 
// Create the request object 
var xml = new XMLHttpRequest(); 
// Open the asynchronous POST request 
//xml.open("GET", "/some/url.cgi", true); 
xml.open("GET",options.url, true); 
// We're going to wait for a request for 5 seconds, before giving up 
var timeoutLength = 5000; 
// Keep track of when the request has been succesfully completed 
var requestDone = false; 
// Initalize a callback which will fire 5 seconds from now, cancelling 
// the request (if it has not already occurred). 
setTimeout(function(){ 
requestDone = true; 
}, timeoutLength); 
// Watch for when the state of the document gets updated 
xml.onreadystatechange = function(){ 
// Wait until the data is fully loaded, 
// and make sure that the request hasn't already timed out 
if ( xml.readyState == 4 && !requestDone ) { 
// Check to see if the request was successful 
if ( httpSuccess( xml ) ) { 
// Execute the success callback with the data returned from the server 
options.onSuccess( httpData( xml, options.type ) ); 
// Otherwise, an error occurred, so execute the error callback 
} else { 
options.onError(); 
} 
// Call the completion callback 
options.onComplete(); 
// Clean up after ourselves, to avoid memory leaks 
xml = null; 
} 
}; 
// Establish the connection to the server 
xml.send(); 
// Determine the success of the HTTP response 
function httpSuccess(r) { 
try { 
// If no server status is provided, and we're actually 
// requesting a local file, then it was successful 
return !r.status && location.protocol == "file:" || 
// Any status in the 200 range is good 
( r.status >= 200 && r.status < 300 ) || 
// Successful if the document has not been modified 
r.status == 304 || 
// Safari returns an empty status if the file has not been modified 
navigator.userAgent.indexOf("Safari") >= 0 && typeof r.status == "undefined"; 
} catch(e){} 
// If checking the status failed, then assume that the request failed too 
return false; 
} 
// Extract the correct data from the HTTP response 
function httpData(r,type) { 
// Get the content-type header 
var ct = r.getResponseHeader("content-type"); 
// If no default type was provided, determine if some 
// form of XML was returned from the server 
var data = !type && ct && ct.indexOf("xml") >= 0; 
// Get the XML Document object if XML was returned from 
// the server, otherwise return the text contents returned by the server 
data = type == "xml" || data ? r.responseXML : r.responseText; 
// If the specified type is "script", execute the returned text 
// response as if it was JavaScript 
if ( type == "script" ) 
eval.call( window, data ); 
// Return the response data (either an XML Document or a text string) 
return data; 
} 
} 
 
在同等目录中，我们可以建立一个rss.xml文件，用这个函数来访问。 
rss.xml如下： 
 代码如下:

<titles> 
<title> 
缘份 
</title> 
<title> 
月亮 
</title> 
<title> 
缘份月亮 
</title> 
</titles> 
 
再建立一个html文档，调用它，就能看到rss.xml中的内容就能被访问到。 
整体看看，其实真的比较简洁和简单。不仅是能访问xml格式文件，html，.js格式的文件都可以调用的； 
这些都可以在本地建立对应的文件，进行调用，都可以实现。
 
 




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