图像Ping

只要请求完成,就能得到通知,发送一个name参数,常用于跟踪用户点击页面或动态广告曝光次数.

缺点:

1.只能发送GET 请求

2.无法访问服务器的响应文本

    <script>
        var img = new Image();
        img.onload = img.onerror = function(){
            alert("Done!");
        };
        img.src = "http://www.example.com/test?name=Nicholas"; 

    </script>

JSONP

JSONP是通过动态<script>元素来使用,可以为其src属性指定一个跨域URL

    <script>
    
        function handleResponse(response){
            alert("You're at IP address " + response.ip + ", which is in " + response.city + ", " + response.region_name);
        }
    
        var script = document.createElement("script");
        script.src = "http://freegeoip.net/json/?callback=handleResponse";
        document.body.insertBefore(script, document.body.firstChild);
    </script>

优点:可以直接访问响应文本

在使用非Web服务时，要保证其安全可靠

要确定JSONP请求是否失败也不容易

Comet

IE不支持

    <script>
    
        function createStreamingClient(url, progress, finished){        
            
            var xhr = new XMLHttpRequest(),
                received = 0;
                
            xhr.open("get", url, true);
            xhr.onreadystatechange = function(){
                var result;
                
                if (xhr.readyState == 3){
                
                    //get only the new data and adjust counter
                    result = xhr.responseText.substring(received);
                    received += result.length;
                    
                    //call the progress callback
                    progress(result);
                    
                } else if (xhr.readyState == 4){
                    finished(xhr.responseText);
                }
            };
            xhr.send(null);
            return xhr;
        }

        var client = createStreamingClient("streaming.php", function(data){
                        alert("Received: " + data);
                     }, function(data){
                        alert("Done!");
                     });
        
    </script>

CORS

        function createCORSRequest(method, url){
            var xhr = new XMLHttpRequest();
            if ("withCredentials" in xhr){
                xhr.open(method, url, true);
            } else if (typeof XDomainRequest != "undefined"){
                xhr = new XDomainRequest();
                xhr.open(method, url);
            } else {
                xhr = null;
            }
            return xhr;
        }

        var request = createCORSRequest("get", "http://www.somewhere-else.com/xdr.php");
        if (request){
            request.onload = function(){
                //do something with request.responseText
            };
            request.send();
        }

确保XHR访问的URL安全

1.要求以SSL连接来访问可以通过XHR请求的资源

2.要求每一次请求都要附带验证码

注意,以下方法无效,很容易伪造

1.要求发送POST

2.检查来源URL

3.基于cookie

不要把用户名和密码放在javascrip里