HTTP HEAD Request in Javascript/Ajax?

Question

Is it possible to do a HTTP Head request solely using an XMLHTTPRequest in JavaScript?

My motivation is to conserve bandwidth.

If not, is it possible to fake it?

Solution

Easy, just use the HEAD method, instead of GET or POST:

function UrlExists(url, callback)
{
    var http = new XMLHttpRequest();
    http.open('HEAD', url);
    http.onreadystatechange = function() {
        if (this.readyState == this.DONE) {
            callback(this.status != 404);
        }
    };
    http.send();
}

This is just a short example to show how to use the HEAD method. Production code may need more fine-grained callbacks for different result states (success, failure, timeout), and may use different event handlers (onload, onerror and ontimeout rather than onreadystatechange).