It's absolutely supported. IE will wait patiently for data to be received, just like other browsers. It'll do keep-alive also with XHR, so you get that benefit

It's absolutely supported. IE will wait patiently for data to be received, just like other browsers. It'll do keep-alive also with XHR, so you get that benefit as well. You can also remove some HTTP headers in js to get some bandwidth optimization :) One possibility you may be thinking of is XHR reuse, which is a pain in IE, as far as I remember there's a couple of bugs if you try to reuse the same XHR object. There's hoops to jump through depending on the state or something, and it's just more reliable to not reuse the object on IE. At the moment, I create a new XHR object for each request, to be sure there aren't issues with IE (I believe XHR reuse isn't an issue on other browsers).