Set Bootstrap Datepicker to focusDate when tabbing out

datepicker_patch.js

# datepicker is accessible trough data("datepicker")
# but its focusDate is cleared out on keydown for tab (9)
# my solution is thus to store the focusDate as data('datepicker_focusdate') on keydown when the key is a navigation key (up, down, left, right)
# and then set the datepicker date to that date when tabbing out

	$("body").on("keydown", '[data-provide~=datepicker]', function(e){
		if ([37,38,39,40].indexOf(e.keyCode) >= 0 ) {
			$(this).data('datepicker_focusdate', $(this).data("datepicker").focusDate)
		} else if (e.keyCode == 9 && $(this).data('datepicker_focusdate')) {
			$(this).datepicker('update', $(this).data('datepicker_focusdate'));
		}
	});

Updated to avoid setting the field to blank when the first keydown is tab