> native JS `XMLHttpRequest` was only available from IE 7 onwards, before that it was some ActiveX thing.
replyAlmost sure it was available on IE6. But even if not, you could emulate it using hidden iframes to call pages which embedded some javascript interacting with the main page. I still have fond memories of using mootools for lightweight nice animations and less fond ones of dojo.
Internet Explorer 5–6 was the ActiveX control. Then other browsers implemented XMLHTTPRequest based on how that ActiveX control worked, then Internet Explorer 7 implemented it without ActiveX the same way as the other browsers, and then WHATWG standardised it.
replyKuro5hin had a dynamic commenting system based on iframes like you describe.