javascript-AJAX请求状态返回0

当我使用此代码发出AJAX请求时,它返回状态为0.我做错了什么？另外,出于各种原因,此代码仅设计用于Firefox.

var ajax;

function connectToOtherServer(server,port,userid,password){

ajax=new XMLHttpRequest();
ajax.onreadystatechange=validateConnection;

params='userid='+encodeURIComponent(userid)+'&password='+encodeURIComponent(password);

alert('http://'+server+':'+port+'/ok.txt');

ajax.open('POST','http://'+server+':'+port+'/ok.txt',true);

ajax.setRequestHeader("Content-type","application/x-www-form-urlencoded");
ajax.setRequestHeader("Content-length",params.length);
ajax.setRequestHeader("Connection","close");

ajax.send(params);

}

function validateConnection(){
if(ajax.readyState===4){
if(ajax.status===200){

alert(ajax.responseText);

}else{
alert(ajax.status);
}
}
}

解决方法:

如果您尝试连接到另一台服务器,则same origin policy将阻止您：

The term “origin” is defined using the
domain name, application layer
protocol, and (in most browsers) TCP
port of the HTML document running the
script. Two resources are considered
to be of the same origin if and only
if all these values are exactly the
same.