将AJAX从浏览器用于外部地址（即在浏览器外部，即使它是localhost）也很容易，但我有一个不同的问题。
是否存在允许浏览器向自身发出（或模拟）HTTP请求的某种对象或服务，例如来自JavaScript？
E.g。从Firefox我可以看到以下原始请求：
GET /headers.php HTTP/1.1
Host: localhost
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:49.0) Gecko/20100101 Firefox/49.0
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
Accept-Language: en-GB,en;q=0.5
Accept-Encoding: gzip, deflate
Connection: keep-alive
Upgrade-Insecure-Requests: 1
Cache-Control: max-age=0
使用PHP脚本（headers.php请求中提到的GET）：
<pre>
<?php
print_r(apache_request_headers ());
我可以在页面上看到以下内容：
[Content-Type] =>
[Content-Length] => 0
[Upgrade-Insecure-Requests] => 1
[User-Agent] => Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:49.0) Gecko/20100101 Firefox/49.0
[Host] => localhost
[Accept-Language] => en-GB,en;q=0.5
[Accept-Encoding] => gzip, deflate
[Accept] => text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
[Connection] => keep-alive
[Cache-Control] => max-age=0
我是否可以通过JavaScript获取相同的信息，而无需调用服务器脚本？