function createXML(){
    if(typeof XMLHttpRequest != "undefined"){//标准
        return new XMLHttpRequest();
    }else if(typeof ActiveXObject != "undefined"){//兼容IE5，IE6
        if(typeof arguments.callee.activeXString != "string"){            
        var versions = ["MSXML2.XMLHttp.6.0","MSXML2.XMLHttp.3.0","MSXML2.XMLHttp"],i,len;            
        for (i=0,len=versions.length; i < len; i++) {                
        try{                    
        new ActiveXObject(versions[i]);                    
        arguments.callee.activeXString = versions[i];                    
        break;
                }catch(ex){                    //跳过
                }
            }
        }        
        return new ActiveXObject(arguments.callee.activeXString);
    }else{        
    throw new Error("no XRL object available.");
    }
}var xml = new createXML();

xml.setRequestHeader("Content-Type","text/plain");

xml.send(null);

var xml = new createXML();xml.open("get","hello-world.html",false);xml.onreadystatechange = function(url,callback){    if(xml.readyState === 4){        if((xml.status >= 200 && xml.status < 300) || xml.status === 304){
            console.log(xml.responseText);
        }else{
            console.log("request is not ok" + xml.status);
        }
    }
}xml.send(null);

xml.setRequestHeader("MyHeader","MyValue");

function addURLParam(url,name,value){
    url += (url.indexOf(?) == -1 ? "?" : "&");
    url += encodeURIComponent(name) + "=" +encodeURIComponent(value);    
    return url;
}

function submitData(){    
    var xml = createXML();    
    xml.onreadystatechange = function(){        
    if(xml.readyState === 4){            
    if((xml.status >= 200 && xml.status < 300) || xml.status === 304){
                console.log(xml.responseText);
            }else{
                console.log("request is not ok" + xml.status);
            }
        }
    }    
    xml.open("POST","postexample.php",true);    
    xml.setRequestHeader("Content-Type","application/x-www-form-urlencoded");//原因见表单编码的请求一节
    var form = document.getElementById("user-info");    
    xml.send(serialize(form));//serialize函数用来将页面中的表单数据格式化}

function encodeFormData(data){
    if(!data) return "";//无数据就返回空串
    var pairs = [];//用来保存键值对
    for(var name in data){        if(!data.hasOwnProperty(name)) continue;//跳过继承属性
        if(typeof data[name] === "function") continue;//跳过方法
        var value = data[name].toString();
        name = encodeURIComponent(name.replace(/%20/g,"+"))//因为由于历史原因，表单提交的 x-www-form-urlencoded 格式要求空格编码为 + 。但 encodeURIComponent 是遵照后来的标准编码为 %20 的。
        value = encodeURIComponent(value.replace(/%20/g,"+"))
        pairs.push(name + "=" + value);
    }    return paris.join('&')//连接键值对}function getData(url,data,callback){
    var request = new XMLHttpRequest()
    request.open("GET",url+"?"+encodeFormData(data))
    request.onreadystatechange = function(){
        if(request.readyState === 4 && callback) callback(request)
    }
    request.send(null);
}function postData(url,data,callback){
    var request = new XMLHttpRequest();
    request.open("POST",url);
    request.onreadystatechange = function(){
        if(request.readyState === 4 && callback){
            callback(request);
        }
    }
    request.setRequestHeader("Content-Type","application/x-www-form-urlencoded");
    request.send(encodeURIComponent(data));
}

function postJson(url,data,callback){
    var request = new XMLHttpRequest();    
    request.open("POST",url);    
    request.onreadystatechange = function(){        
    if(request.readyState === 4 && callback){
            callback(request);
        }
    }    request.setRequestHeader("Content-Type","application/json");    
        request.send(JSON.stringify(data));
}

input.addEventListener("change",function(){//添加事件监听
    var file = this.file[0];    
    var xhr = new XMLHttpRequest();
    xhr.open("POST",URL);
    xhr.send(file);
},false)

function postData(url,data,callback){
    var request = new XMLHttpRequest();
    request.open("POST",url);
    request.onreadystatechange = function(){
        if(request.readyState === 4 && callback){
            callback(request);
        }
    }    var form = document.getElementById("user-info");
    request.send(new FormData(form));
}

var xml = new createXML();xml.onload = function(event){    
    if((xml.status >= 200 && xml.status < 300) || xml.status === 304){        
    var request = document.getElementById("request");
        request.innerHTML = xml.responseText;
    }else{
        console.log("request is not ok" + xml.status);
    }
}xml.open("get","hello-world.html",false);xml.send(null);

var xml = new createXML();xml.onload = function(event){    
    if((xml.status >= 200 && xml.status < 300) || xml.status === 304){        
    var request = document.getElementById("request");
        request.innerHTML = xml.responseText;

    }else{
        console.log("request is not ok" + xml.status);
    }
}xml.onprogress = function(event){    
    var p = document.getElementById("data");    
    if(event.lengthComputable){
        console.log(event.position);
        p.innerHTML = "Received " + event.loaded + " of " + event.total + " bytes";
    }
}/*需要注意的是，必须保证调用open之前定义onprogress事件处理程序*/xml.open("get","hello-world.html",true);xml.send(null);

function timeGetText(url,timeout,callback){
    var request = new XMLHttpRequest();    
    var timedout = false; //判断是否超时
    var timer = setTimeout(function(){
        timedout = true;//超时
        request.abort();//触发终止事件
    },timeout);//如果超时，触发一个启动器
    request.open("GET",url);//发起请求
    request.onreadystatechange = function(){
        if(request.readyState !== 4) return;//忽略未完成程序
        if(timedout) return;//忽略超时程序
        clearTimeout(timer);//取消等待的超时
        if(request.status === 200){
            callback(request.responseText);//成功
        }
    }
    request.send(null);
}

var img = new Image();
img.onload = img.onerror = function(){
    console.log("Done!");
};
img.src = "hello-world.html";

var bd = document.body;function callbackFunction(result, methodName)
   {
       bd.innerText = result;
   }
   var script = document.createElement("script");
   script.src = "***/jsonp.php?jsoncallback=callbackFunction";
   bd.insertBefore(script,bd.firstChild);

function getJSONP(url,callback){
    var cbnum = "cb" + getJSONP.counter++;    
    var cbname = "getJSONP." + cbnum;    
    if(url.indexOf("?") === -1){
        url += "?jsonp=" + cbname;
    }else{
        url += "&jsonp=" + cbname;
    }    var script = document.createElement("script");
    getJSONP[cbname] = function(response){
        try{
            callback(response);
        }        finally{            delete getJSONP[cbname];
            script.parentNode.removeChild(script);
        }
    }
    script.src = url;
    document.body.appendChild(script);
}
getJSONP.counter = 0;

function createStreamingClient(url, progress/*接收到数据时调用的函数*/, finished/*关闭连接时调用的函数*/) {
    var xhr = new XMLHttpRequest(),
        received = 0;
    xhr.open("get", url, true);
    xhr.onreadystatechange = function() {
        var result;        if (xhr.readyState == 3) {
            result = xhr.responseText.substring(received);
            received += result.length;
            progress(result);
        } else if (xhr.readyState == 4) {
            finished(xhr.responseText);
        }
    };
    xhr.send(null);    return xhr;
}var client = createStreamingCilent("streaming.php", function(data) {
    alert("Received:" + data);
}, function(data) {
    alert("Done!");
});

var source = new EventSource("myevents.php");/*必须同源*/

var Socket = new WebSocket(url, [protocol]/*可接受的子协议*/ );//创建对象