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Because AJAX is normally processed asynchronously we
may have situations where we want to stop waiting for
the responce to come back from the server because it is
no longer relevant. The situation where your visitor
leaves the page before the response is received is
handled by the automatic deletion of the request object
along with the rest of the page so the situation where
we are most likely to need to abort a prior request is
when our visitor wants to make a new request (for
example they have changed their mind about which option
they wanted).
A minor alteration to the code where we create a new
ajax object can readily allow our object to be reused
after aborting any outstanding request. Here is the
code that we need to replace:
var ajaxObj = createXMLHttp();
By replacing this statement with an if statement to
test if the object already exists and to abort any
exiting request we can reuse an existing object where
one already exists and avoid problems with multiple
requests to the server.
if (!ajaxObj)
ajaxObj = createXMLHttp();
else if (ajaxObj.readyState != 0)
ajaxObj.abort();
After running this piece of code if doesn't matter
whether a prior request existed as the state of the
AJAX object after running this code is the same
regardless of whether the object previously existed or
has been newly created.
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