xmlhttprequest not firing response event handler f

I am sending a request a remote server from google chrom extension using xmlhttprequest

I have set permissions in the manifest.json to access remote hosts

Basically it is working fine as expected. what i had expected is readystate 4 it is fired when the response has completed.

Since it is a 8 to 10 second process in the server side i use echo from the server side to the client for status update.

so i use readyState==3 condition to show server response

but when i tested readystate 1 and 4 are firing the event handler and not 2 and 3

here is the code i use

var wini = window.open('','');
var sta='';
var jax = new XMLHttpRequest();
jax.onreadystatechange = function() {
    sta = sta + jax.readyState + ', '
    wini.document.write(sta+'<br>');

}
jax.open("POST","http://sitename.com/subscript/?save=save&tstamp="+Math.random());
jax.setRequestHeader("Content-Type","application/x-www-form-urlencoded");
//jax.setRequestHeader("Connection: close");
jax.send("somedata=" + encodeURIComponent(window.somedata));

using connection close. a different result. except readystate 1 no others were fired

So, readystates 1 and 4 are working fine but not 2 and 3. what is most needed is 3.

what is actually happens with the code runs is:

1, is printed in the popup window and then 8 to 9 secs pass and when ready state is 4

1,2

1,2,3

1,2,3,4

the above three lines are printed in one shot. so i assume only by readystate 4 i am getting all the response from the server and not while readystate is 3.

I have used readystate 3 in other web applications which is of same origin and it worked and is still working.

for this xhr i don't know what i am missing.

How to make use of readystate 3 here?

at last i found that only in chrome and safari it does not work because chrome is using safari webkit and may be webkit doesn't want to work like others.

added a content type header and it worked as expected

another user had a similar issue and i had been experimenting and found the following solution.

since my solutions solves both the questions i am linking the answer which i had already given in others question instead of duplicating it here.

here is my answer.

PHP Flush() not working in Chrome