How to Fire an event when the user navigate out of a page?

I am building an "Edit page". When the user enter the Id he wants to edit, a new record in a LOCK table is inserted to disable further editing requests in the same time  ( I don't want that 2 users edit the same thing at the same time). So the problem is: how could I fire an event that will deletes the record from the LOCK table when the user navigate out of the edit page?
 
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