jQuery progress handler

progress.js

$.ajax({
    type: 'POST',
    url: '/files/upload', 
    /* jQuery automatically processes and transforms Ajax data into a querystring.
     * It should not do that with our binary data. */
    processData: false,
    data: file,
    /* The 'upload' object and onprogress event are part of the new XmlHttpRequest (XHR) 2.
     * With jQuery v1.7.2 there's no direct way to access this event, 
     * so we need to manually access the core XmlHttpRequest object to attach an event handler. 
     *
     * 15 aug 2012: XHR 2 is still relatively new, so be sure to check which browsers you intend to support.
     * For example, Internet Explorer doesn't support it in version 9 and below.
     * For a full support chart, see http://caniuse.com/xhr2 */
    xhr: function() {
        extendedXhr = $.ajaxSettings.xhr();
        if( extendedXhr.upload ){
            extendedXhr.upload.onprogress = function( e ){
                /* Only handle progress if the currently uploaded size is known */
                if( !e.lengthComputable ) return;
                            
                console.log( e.loaded / e.total );
            }
        }
        return extendedXhr;
    }
});