These docs are for an old release. Info on upgrading to v4
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prev

Moves the calendar one step back (by a month or week for example).

.fullCalendar( ‘prev’ )

If the calendar is in month view, will move the calendar back one month.

If the calendar is in basicWeek or agendaWeek, will move the calendar back one week.

If the calendar is in basicDay or agendaDay, will move the calendar back one day.

Example using prev with an external button:

$('#my-prev-button').click(function() {
  $('#calendar').fullCalendar('prev');
});

View a demo that uses the prev and next methods.