XMLHttpRequest 2

Compatibility table for support of XMLHttpRequest 2 in desktop and mobile browsers.

http://caniuse.com/xhr2

cross-site xmlhttprequest with CORS

https://hacks.mozilla.org/2009/07/cross-site-xmlhttprequest-with-cors/

How to detect if the new HTML5 File Upload progress information is available in your browser

if (!!window.ProgressEvent && !!window.FormData) {
             alert('File upload progress supported');
} else {
             alert('No file upload progress support');
}

Modernizr

var progEv = !!(window.ProgressEvent);
var fdata = !!(window.FormData);
setResult('xhr20', (progEv && fdata));