最近学习js，肯定会学到ajax中的东西，所以，看到比较好的ajax函数，免不得要贴出来，供大家参考。这个函数摘录自john resig的书中。

核心ajax（options）函数中，包含了建立xmlhttprequest,提取数据，判断是否回复成功等，基本满足了日常需求。

// 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：

<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。

• ajax
• 框架