在 JavaScript 中设置请求标头

在使用 XMLHttpRequest 进行 AJAX 调用时，我似乎无法从 JavaScript 更改大多数请求标头.请注意，当必须在 Gecko 浏览器中的 request.open() 之后调用 request.setRequestHeader 时(请参阅 http://ajaxpatterns.org/Talk:XMLHttpRequest_Call).当我设置 Referer 时，它没有被设置(我查看了使用 Firebug 和 Tamper Data 发送的请求标头).当我设置 User-Agent 时，它完全搞砸了 AJAX 调用.但是，设置 Accept 和 Content-Type 确实有效.我们是否无法在 Firefox 3 中设置 Referer 和 User-Agent?

It seems that I am unable to change most request headers from JavaScript when making an AJAX call using XMLHttpRequest. Note that when request.setRequestHeader has to be called after request.open() in Gecko browsers (see http://ajaxpatterns.org/Talk:XMLHttpRequest_Call). When I set the Referer, it doesn't get set (I looked at the request headers sent using Firebug and Tamper Data). When I set User-Agent, it messed up the AJAX call completely. Setting Accept and Content-Type does work, however. Are we prevented from setting Referer and User-Agent in Firefox 3?

var request = new XMLHttpRequest();
var path="http://www.yahoo.com";
request.onreadystatechange=state_change;

request.open("GET", path, true);
request.setRequestHeader("Referer", "http://www.google.com");
//request.setRequestHeader("User-Agent", "Mozilla/5.0");
request.setRequestHeader("Accept","text/plain");
request.setRequestHeader("Content-Type","text/plain");

request.send(null);
    function state_change()
{
if (request.readyState==4)
  {// 4 = "loaded"
  if (request.status==200)
    {// 200 = OK
    // ...our code here...
    alert('ok');
    }
  else
    {
    alert("Problem retrieving XML data");
    }
  }
}