How to send AJAX header

How to set and get header either JS or AJAX

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");

and

var headers = req.getAllResponseHeaders().toLowerCase();