How do I know which button is clicked when the bootstrap modal closes?

Answer 1

To extend @JoshCrozier's answer:

It would be nice if they had a property like that associated with the hide.bs.modal/hidden.bs.modal events. As of writing this, there currently isn't

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This will emulate a similar behaviour, that attaches the clicked button as relatedTarget for later listeners:

$( '.modal-footer .btn[data-dismiss="modal"]' ).on( 'click', function() {
    var target = this

    $( target ).closest( '.modal' )
        .one( 'hide.bs.modal hidden.bs.modal', function( event ) {
            event.relatedTarget = target
        } )
} )

The selector and listener can be further optimized depending on how the modals are used in a project. For example: if you know you're not going to use hide.bs.modal you can just modify hidden.bs.modal's event instead.