[ahlschwede]

Before Ajax one way to do Web 2.0 style interactions was to hide a Java applet in an invisible iFrame and feed data back and forth from the page using JavaScript.

I think people forget that the early web had a proliferation of plug-ins. JavaScript was most often used as glue between HTML and plug-ins which had fewer platform incompatibilities than the browsers. One of the reasons Flash became the dominant plug-in was because it was universal enough to duplicate the features of other plug-ins, including asynchronous communication via Java applet.

[moron4hire]

IFrames were invented later (and initially, only in IE). You also didn't ever need to put the applet in a separate frame. You could just put the applet on the page. Indeed, putting it in a frame would have defeated the purpose, because there was no way to communicate across frames at the time.