Stop jquery ajax request in ajaxStart

.ajaxStart doesn't have access to the xhr object. .ajaxSend does, however. You can stop it there. I don't know why you would want to do this, but remember that this is a global ajax event -- so this effectively stops all ajax requests(or at least those that don't have the global:false flag).

$('some-object').ajaxSend(function(e, xhr) {
    xhr.abort();
});

FYI there's a third argument also which is the Ajax Options object used to create the request in case that is of help...

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$('some-object').ajaxSend(function(e, xhr, options) {
    xhr.abort();
});