How can we send/get the http headers information with AJAX?

Is there any way to send/get the http headers (like, content-type... ) through AJAX?. Then, can please explain me, what will we archive by passing the http headers in AJAX and where wil开发者_运维问答l use this technique?.

Thanks

I'm no expert,

But you should look at the AJAX object XmlHttpHeader and the wikipedia article here.

EDIT: quoting the www.w3.org reference:

function test(data) {
 // taking care of data
}

function handler() {
 if(this.readyState == 4 && this.status == 200) {
  // so far so good
  if(this.responseXML != null && this.responseXML.getElementById('test').firstChild.data)
     // success!
   test(this.responseXML.getElementById('test').firstChild.data);
  else
   test(null);
 } else if (this.readyState == 4 && this.status != 200) {
  // fetched the wrong page or network error...
  test(null);
 }
}

var client = new XMLHttpRequest();
client.onreadystatechange = handler;
client.open("GET", "unicorn.xml");
client.send();

If you just want to log a message to the server:

function log(message) {
 var client = new XMLHttpRequest();
 client.open("POST", "/log");
 client.setRequestHeader("Content-Type", "text/plain;charset=UTF-8");
 client.send(message);
}

Or if you want to check the status of a document on the server:

function fetchStatus(address) {
 var client = new XMLHttpRequest();
 client.onreadystatechange = function() {
  // in case of network errors this might not give reliable results
  if(this.readyState == 4)
   returnStatus(this.status);
 }
 client.open("HEAD", address);
 client.send();
}