Question

Is it possible to gather the HTTP headers in JavaScript ?
This is just a thought of mine after using Firebug for days.
In one of the posts I came to know that, it is impossible to find the HTTP headers in JavaScript, whereas in firebug, we can see the response headers (client side)

so my question is can we cache the HTTP headers in JavaScript ?

Answer 1

The HTTP headers aren’t available in JavaScript.

However you could use XMLHttpRequest to do a HEAD request to any resource within the same domain:

var xhr = new XMLHttpRequest();

xhr.open('HEAD', '/', true);            // Relative path of resource

xhr.onreadystatechange = function() {
  if (xhr.readyState === 4) {
    console.log(xhr.getAllResponseHeaders());
  }
}

xhr.send(null);

The above will return something like this (running it in Firebug on this page):

Server: nginx 
Date: Fri, 09 Jul 2010 18:58:30 GMT 
Content-Type: text/html; charset=utf-8 
Connection: keep-alive 
Cache-Control: public, max-age=60 
Content-Length: 33273 
Content-Encoding: gzip 
Expires: Fri, 09 Jul 2010 18:59:31 GMT 
Last-Modified: Fri, 09 Jul 2010 18:58:31 GMT 
Vary: * 

You can easily get the value of single headers like this:

xhr.getResponseHeader('Last-Modified');