Since post() doesn't have a return statement, the onsubmit function ends up returning undefined.
Since it doesn't return false, it doesn't cancel the normal behaviour of the form. Consequently, the form submits and unloads the page before the Ajax request resolves.
Putting in an alert delays the page unload until you click OK, which gives time for the Ajax request to resolve.
return false from the post function to cancel the normal submission of the form instead.
