Send an Ajax Call on beforeunload/unload
问题 Scenario: I am creating an event registration module in which a user would choose a date from a calendar for booking, fill some input fields and pay up to book the date. One of the requirements is that, there can be only one booking per date. This arises a case where two people want to book the same date on the same time. So, we need to show the user who came later to book the date a message that a booking is already in progress for that specific date. Please check back later . For this to