How to call events on clicking prev and next button?

I see there are other working answers, but IMHO the simplest and more correct - at least using FullCalendar v.4 - is to intercept prev and next is to deal them in the same way of custom buttons.

Here my setup (using toastr just for demo purposes)

document.addEventListener('DOMContentLoaded', function() {
  var calendarEl = document.getElementById('calendar');

  var calendar = new FullCalendar.Calendar(calendarEl, {
    plugins: [ 'dayGrid', 'timeGrid' ],
    header: {
      left: 'dayGridMonth,timeGridWeek,timeGridDay',
      center: 'title',
      right: 'prev,next'
    },
    footer: {
      left: '',
      center: '',
      right: 'prev,next'
    },
    customButtons: {
      prev: {
        text: 'Prev',
        click: function() {
                    // so something before
                    toastr.warning("PREV button is going to be executed")
                    // do the original command
                    calendar.prev();
                    // do something after
                    toastr.warning("PREV button executed")
        }
      },
      next: {
        text: 'Next',
        click: function() {
                    // so something before
                    toastr.success("NEXT button is going to be executed")
                    // do the original command
                    calendar.next();
                    // do something after
                    toastr.success("NEXT button executed")
        }
      },
    }
  });

  calendar.render();
});

See a Codepen here

SOLUTION IN FULLCALENDAR VERSION 5:

If you're using version 5 of FullCalendar, I will suggest u to use the datesSet instead of using the .click().

datesSet: function() {
    myFunction();
}

The myFunction() will be called every time when the date range of calendar has been changed or initialised. In other word, when u click on the provided prev/next buttons in the calendar, the calendar's date range will be changed and the myFunction() will be called.

reference: https://fullcalendar.io/docs/datesSet

If u really want to go with the .click() way, the following code is working for version 5 of FullCalendar.

$('.fc-prev-button').click(function(){
    myFunction();
});

$('.fc-next-button').click(function(){
    myFunction();
});

Both methods are perfectly work in my project (VERSION 5 OF FULLCALENDAR), hope this can help people who are struggling with the issue.

Version 3 the answer is to use:

viewRender: function (event, element, view){
// you code here
}

Version 4: https://fullcalendar.io/docs/v4/datesRender

datesRender: function (){
    // you code here
    }

https://fullcalendar.io/docs/v4/upgrading-from-v3

"viewRender Renamed to datesRender. Parameters have changed."

Version 5 Use :

datesSet: function (){
    // you code here
    }

"datesRender changed to: datesSet - renamed from datesRender. Called after a view's dates are initialized or when they change." https://fullcalendar.io/docs/upgrading-from-v4

Instead of click use on

$('body').on('click', '.fc-prev-button', function() {
});

$('body').on('click', '.fc-next-button', function() {
});

this is useful when your calendar can dynamically initialize at any point of time.

If you didn't make it with the answers above, try this:

$('span.fc-button.fc-button-prev.fc-state-default.fc-corner-left').click(function() {
    alert('prev is clicked, do something');
});

$('span.fc-button.fc-button-next.fc-state-default.fc-corner-right').click(function() {
    alert('next is clicked, do something');
});

FullCalendar v3.4.0

Prev, next. today, week, month buttons:

$(document).ready(function(){

$('#mycalendar').fullCalendar({


$('.fc-prev-button').click(function(){
        alert("Clicked prev button");
    });

    $('.fc-next-button').click(function(){
        alert("Clicked next button");
    });

    $('.fc-today-button').click(function(){
        alert('Today button clicked, do something');
    });

    $('.fc-listWeek-button').click(function(){
        alert('list week clicked, do something');
    });

    $('.fc-listMonth-button').click(function(){
        alert('list month clicked, do something');
    });

});

});