JavaScript异步Ajax技术详解：从原理到实战

variable=new XMLHttpRequest();

variable=new ActiveXObject("Microsoft.XMLHTTP");

var xmlhttp;
if (window.XMLHttpRequest)
{
    //  IE7+, Firefox, Chrome, Opera, Safari 浏览器执行代码
    xmlhttp=new XMLHttpRequest();
}
else
{
    // IE6, IE5 浏览器执行代码
    xmlhttp=new ActiveXObject("Microsoft.XMLHTTP");
}

xmlhttp.open("GET","ajax_info.txt",true);
xmlhttp.send();

xmlhttp.open("GET","ajax_test.html",true);

xmlhttp.open("GET","/try/ajax/demo_get.php",true);
xmlhttp.send();

xmlhttp.open("GET","/try/ajax/demo_get.php?t=" + Math.random(),true);
xmlhttp.send();

xmlhttp.open("GET","/try/ajax/demo_get2.php?fname=Henry&lname=Ford",true);
xmlhttp.send();

xmlhttp.open("POST","/try/ajax/demo_post.php",true);
xmlhttp.send();

xmlhttp.open("POST","/try/ajax/demo_post2.php",true);
xmlhttp.setRequestHeader("Content-type","application/x-www-form-urlencoded");
xmlhttp.send("fname=Henry&lname=Ford");

xmlhttp.open("GET","ajax_test.html",true);

xmlhttp.onreadystatechange=function()
{
    if (xmlhttp.readyState==4 && xmlhttp.status==200)
    {
        document.getElementById("myDiv").innerHTML=xmlhttp.responseText;
    }
}
xmlhttp.open("GET","/try/ajax/ajax_info.txt",true);
xmlhttp.send();

xmlhttp.open("GET","/try/ajax/ajax_info.txt",false);
xmlhttp.send();
document.getElementById("myDiv").innerHTML=xmlhttp.responseText;

document.getElementById("myDiv").innerHTML=xmlhttp.responseText;

xmlDoc=xmlhttp.responseXML;
txt="";
x=xmlDoc.getElementsByTagName("ARTIST");
for (i=0;i<x.length;i++)
{
    txt=txt + x[i].childNodes[0].nodeValue + "<br>";
}
document.getElementById("myDiv").innerHTML=txt;

xmlhttp.onreadystatechange=function()
{
    if (xmlhttp.readyState==4 && xmlhttp.status==200)
    {
        document.getElementById("myDiv").innerHTML=xmlhttp.responseText;
    }
}

function myFunction()
{
    loadXMLDoc("/try/ajax/ajax_info.txt",function()
    {
        if (xmlhttp.readyState==4 && xmlhttp.status==200)
        {
            document.getElementById("myDiv").innerHTML=xmlhttp.responseText;
        }
    });
}

// This is a list of XMLHttpRequest-creation factory functions to try
HTTP._factories = [
    function() { return new XMLHttpRequest(); },
    function() { return new ActiveXObject("Msxml2.XMLHTTP"); },
    function() { return new ActiveXObject("Microsoft.XMLHTTP"); }
];

// When we find a factory that works, store it here.
HTTP._factory = null;

// Create and return a new XMLHttpRequest object.
//
// The first time we're called, try the list of factory functions until
// we find one that returns a non-null value and does not throw an
// exception. Once we find a working factory, remember it for later use.
//
HTTP.newRequest = function() {
    if (HTTP._factory != null) return HTTP._factory();

    for(var i = 0; i < HTTP._factories.length; i++) {
        try {
            var factory = HTTP._factories[i];
            var request = factory();
            if (request != null) {
                HTTP._factory = factory;
                return request;
            }
        }
        catch(e) {
            continue;
        }
    }
    // If we get here, none of the factory candidates succeeded,
    // so throw an exception now and for all future calls.
    HTTP._factory
 = function() {
        throw new Error("XMLHttpRequest not supported");
    }
    HTTP._factory(); // Throw an error
}

HTTP.get = function(url, callback, options) {
    var request = HTTP.newRequest();
    var n = 0;
    var timer;
    if (options.timeout)
        timer = setTimeout(function() {
                               request.abort();
                               if (options.timeoutHandler)
                                   options.timeoutHandler(url);
                           },
                           options.timeout);

    request.onreadystatechange = function() {
        if (request.readyState == 4) {
            if (timer) clearTimeout(timer);
            if (request.status == 200) {
                callback(HTTP._getResponse(request));
            }
            else {
                if (options.errorHandler)
                    options.errorHandler(request.status,
                                         request.statusText);
                else callback(null);
            }
        }
        else if (options.progressHandler) {
            options.progressHandler(++n);
        }
    }

    var target = url;
    if (options.parameters)
        target += "?" + HTTP.encodeFormData(options.parameters)
    request.open("GET", target);
    request.send(null);
};

//getText()工具
HTTP.getText = function(url, callback) {
var request = HTTP.newRequest();
request.onreadystatechange = function() {
if(request.readyState == 4 && request.status == 200) {
callback(request.responseText);
}
}


request.open("GET", url);
request.send(null);
}


//getXML()工具
HTTP.getXML = function(url, callback) {
var request = HTTP.newRequest();
request.onreadystatechange = function() {
if(request.readyState == 4 && request.status == 200) {
callback(request.responseXML);
}
}


request.open("GET", url);
request.send(null);
}

/**
 * Send an HTTP POST request to the specified URL, using the names and values
 * of the properties of the values object as the body of the request.
 * Parse the server's response according to its content type and pass
 * the resulting value to the callback function. If an HTTP error occurs,
 * call the specified errorHandler function, or pass null to the callback
 * if no error handler is specified.
 **/
HTTP.post = function(url, values, callback, errorHandler) {
    var request = HTTP.newRequest();
    request.onreadystatechange = function() {
        if (request.readyState == 4) {
            if (request.status == 200) {
                callback(HTTP._getResponse(request));
            }
            else {
                if (errorHandler) errorHandler(request.status,
                                               request.statusText);
                else callback(null);
            }
        }
    }

    request.open("POST", url);
    // This header tells the server how to interpret the body of the request.
    request.setRequestHeader("Content-Type",
                             "application/x-www-form-urlencoded");
    // Encode the properties of the values object and send them as
    // the body of the request.
    request.send(HTTP.encodeFormData(values));
};

HTTP.getHeaders = function(url, callback, errorHandler) {
    var request = HTTP.newRequest();
    request.onreadystatechange = function() {
        if (request.readyState == 4) {
            if (request.status == 200) {
                callback(HTTP.parseHeaders(request));
            }
            else {
                if (errorHandler) errorHandler(request.status,
                                               request.statusText);
                else callback(null);
            }
        }
    }
    request.open("HEAD", url);
    request.send(null);
};

// Parse the response headers from an XMLHttpRequest object and return
// the header names and values as property names and values of a new object.
HTTP.parseHeaders = function(request) {
    var headerText = request.getAllResponseHeaders();  // Text from the server
    var headers = {}; // This will be our return value
    var ls = /^"s*/;  // Leading space regular expression
    var ts = /"s*$/;  // Trailing space regular expression

    // Break the headers into lines
    var lines = headerText.split(""n");
    // Loop through the lines
    for(var i = 0; i < lines.length; i++) {
        var line = lines[i];
        if (line.length == 0) continue;  // Skip empty lines
        // Split each line at first colon, and trim whitespace away
        var pos = line.indexOf(':');
        var name = line.substring(0, pos).replace(ls, "").replace(ts, "");
        var value = line.substring(pos+1).replace(ls, "").replace(ts, "");
        // Store the header name/value pair in a JavaScript object
        headers[name] = value;
    }
    return headers;
};

/**
 * Encode the property name/value pairs of an object as if they were from
 * an HTML form, using application/x-www-form-urlencoded format
 */
HTTP.encodeFormData = function(data) {
    var pairs = [];
    var regexp = /%20/g; // A regular expression to match an encoded space

    for(var name in data) {
        var value = data[name].toString();
        // Create a name/value pair, but encode name and value first
        // The global function encodeURIComponent does almost what we want,
        // but it encodes spaces as %20 instead of as "+". We have to
        // fix that with String.replace()
        var pair = encodeURIComponent(name).replace(regexp,"+") + '=' +
            encodeURIComponent(value).replace(regexp,"+");
        pairs.push(pair);
    }

    // Concatenate all the name/value pairs, separating them with &
    return pairs.join('&');
};

HTTP._getResponse = function(request) {
switch(request.getResponseHeader("Content-Type")) {
case "text/xml":
return request.responseXML;

case "text/json":
case "text/javascript":
case "application/javascript":
case "application/x-javascript":
return eval(request.responseText);

default:
return request.responseText;
}
}

//提交表单，调用POST方法
var uname = document.getElementById("username");
var usex = document.getElementById("sex");
var formdata = {'username':'tom','sex':'男'};
    HTTP.post("./test.php",formdata, doFun, errorFun);
//请求获取指定的URL的headers
 HTTP.getHeaders("./a.html", doFun, errorFun);