我在使用下面的代码时遇到问题，每当我尝试从网站请求 JSON 数据时，我总是会得到响应代码 0。有人知道为什么吗？如果我要访问该网站，我只需输入正确的登录信息即可获取数据。
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<title></title>
<script type="text/javascript" src="https://ajax.googleapis.com/ajax/libs/jquery/1.7.2/jquery.min.js"></script>
<script src="Base64.js" type="text/javascript"></script>
<script type="text/javascript">
function alertContents(HTTPobj) {
if (HTTPobj.readyState == 4) {
// everything is good, the response is received
if ((HTTPobj.status == 200) || (HTTPobj.status == 0)) {
// FIXME: perhaps a better example is to *replace* some text in the page.
var htmlDoc = document.createElement('div'); // Create a new, empty DIV node.
htmlDoc.innerHTML = HTTPobj.responseText; // Place the returned HTML page inside the new node.
alert("The response was: " + HTTPobj.status + HTTPobj.responseText);
//var jsonData = eval('(' + HTTP.responseText + ')');
//parseJson(HTTP.responseText);
}
else {
alert('There was a problem with the request. ' + HTTPobj.status + HTTPobj.responseText);
}
}
}
}
function makeBaseAuth(user,password) {
var tok = user + ':' + password;
var hash = Base64.encode(tok);
alert(hash);
return "Basic " + hash;
}
function getInput() {
var getUser = document.input.user.value;
var getPass = document.input.pass.value;
var logData = makeBaseAuth(getUser, getPass);
var url = 'http://www.tt-galaxi.com/thubrest/login';
// var url = 'http://www.tt-galaxi.com/thubrest/users/%@/trips',username;
// var url = 'http://www.tt-galaxi.com/thubrest/parkingbays';
var HTTPobj = new XMLHttpRequest();
HTTPobj.onreadystatechange = function () { alertContents(HTTPobj); };
var test = HTTPobj.open('GET', url);
HTTPobj.setRequestHeader('Authorization', logData);
HTTPobj.send();
}
</script>
</head>
<body>
<form name="input" action="">
Username: <input type="text" name="user" />
<br />
Password:<input type="text" name="pass" />
<br />
<input id="Button1" type="button" value="Submit" onclick="getInput()"/>
</form>
</body>
</html>
看起来您正在尝试从与您的来源不同的主机请求数据。为了详细说明这一点，如果您在主机 A 中运行一个名为 www.example.com 的站点，并且您尝试向在主机 B 中运行的 wwww.somethingelse.com 发出请求，您将无法从主机 B 获取数据，因为大多数现代浏览器强制执行同源政策 http://en.wikipedia.org/wiki/Same_origin_policy禁止以跨站点方式使用AJAX请求。如果浏览器检测到这种“非法请求”，它会阻止来自该不同主机的传入数据。
但是，如果您拥有该其他主机，则可以显式地将标头传递给浏览器，这基本上告诉浏览器允许来自该其他主机的跨站点数据。阅读更多相关内容here https://developer.mozilla.org/en/http_access_control#Access-Control-Allow-Headers.
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