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From: Hans-Georg Michna on 13 Feb 2010 13:03
I naively assumed that a call to an XMLHttpRequest with async =
true would lead to the program continuing to run after the
..send() action, i.e. the next line of code executed would be the
one after .send() and the program would continue to run to the
end before any data reception callback would be executed.

The readyState event of XMLHttpRequest triggers the processing
of the received data under the condition that the data has
actually been completely received. But since the data is not
received instantly, I think the JavaScript processor could and
should do other things, i.e. continue to run past the Ajax call.
That, I thought, is the whole purpose of the async parameter in
the XMLHttpRequest's open method.

However, my test in Internet Explorer 8 indicates that it is not
so. Apparently the XMLHttpRequest waits and effectively halts
execution until the data is received.

The callback function is called a few times, whenever the
readyState changes, which is OK. If readyState indicates
successful data reception, a further routine, here
processAjaxResult, is called, that processes the data. But
before that happens and while XMLHttpRequest is waiting for
data, I think other parts of the program should continue to run.

What am I seeing here? Where is the asynchronicity? Or does the
browser always wait for some (I hope smallish) time before it
goes async and resumes executing statements after .send()? Or am
I seeing things?

The basic code sample can be seen and tested at
http://winhlp.com/node/684 . When, in the function
submitButtonClicked, I move statements down after the ajax(...)
call, they are not executed before the incoming data is
processed, which seems wrong to me. Any ideas on this one?

Hans-Georg
From: Jorge on 14 Feb 2010 06:22
On Feb 13, 7:03 pm, Hans-Georg Michna <hans-
georgNoEmailPle...(a)michna.com> wrote:
> (...)

I wonder why so many people insist in making a simple XHR as complex
as... 116 LOCs.
--
Jorge.
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