Quality is delighting customers
One thing you can do is to have an IFrame and set its source to be something like
On the server side, you will then realize that this is a directive to check some status.
If it's ready, return appropriate data, otherwise send back a not ready message.
This sending back data/message is actually a page which has an onLoad
which knows about its container document (the original page)
and can access the necessary functions.
You'll have timing issues (but then again, that's your whole
reason for doing this). In particular, You'll have to have some
timeout and set semaphores in case the server or connection
goes belly up, or the response time is longer than expected
and then returning.