These docs are for an old release. Info on upgrading to v5
edit doc

windowResize

Triggered after the calendar’s dimensions have been changed due to the browser window being resized.

function( view ) { }

The calendar has automatically adapted to the new size when windowResize is triggered.

view is the current View Object.

Within the callback function, this will be set to the calendar’s main element.

Example usage of windowResize:

var calendar = new Calendar(calendarEl, {
  windowResize: function(view) {
    alert('The calendar has adjusted to a window resize');
  }
});