问题描述
我用的是firefox 3.6.10，用firebug来调试
Im using firefox 3.6.10, and firebug to debug
所以，这是我的代码:
var xmlhttp = new XMLHttpRequest();
xmlhttp.open("GET", url,false);
xmlhttp.setRequestHeader('Content-Type', 'text/xml');
xmlhttp.send(null);
alert(xmlhttp.responseXML);
responseXML 始终为空，我已经在来自不同域的多个 URL 上尝试过它.我也尝试过异步，结果是一样的.responseText 总是正确返回，没有问题.
responseXML is always null, and i've tried it on several URLs from different domains. I have also tried it asynchronously, it's the same result. The responseText is always properly returned, no problems with it.
我的目标是获得 responseXML.documentElement.
感谢您的帮助.
编辑-----------
此 javascript 代码是从 Greasemonkey 用户脚本执行的，我将其设置为与请求的 url 相同的来源.我也尝试从萤火控制台执行，再次确保原产地政策.两者都有相同的错误.
讨厌javascript.
EDIT-----------
This javascript code was executed from a Greasemonkey userscript, i made surte its the same origin as the requested url. Also i tried executing from firebug console, again ensuring the origin policy. Same error on both.
Gotta hate javascript.
推荐答案
我敢打赌你违反了同源政策.
I bet you are violating the same origin policy.
对于 XHR，您必须具有相同的协议、域、端口等.因此，如果您在 localhost:8080/app 上运行应用程序，则不能 ajax 到 www.cnn.com.
For XHRs, you must have the same protocol, domain, port, etc. So if you are running an app on localhost:8080/app, you CANNOT ajax to www.cnn.com.
不同的浏览器有不同的处理方式；我看到FF按照你的描述做了，就是请求看起来正常返回但是没有数据...
Different browsers handle this differently; I have seen FF do what you describe, which is the request appears to return normally but there is no data...
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