What is ondelete in angularjs directive definition?

Question

I am reading this article and then encountered the ondelete concept in directive, which I couldn't find the explanation in official document.

app.directive('stickyNote', function(socket) {
  var linker = function(scope, element, attrs) {};
  var controller = function($scope) {};
  return {
    restrict: 'A', 
    link: linker, 
    controller: controller, 
    scope: { 
      note: '=',
      ondelete: '&' // What is ondelete? Where is document? 
    }
  };
});

Can you please help me find the official document to explain ondelete in directive?

Answer 1

Scope has a $destroy event. You may subscribe on it

$scope.$on('$destroy', function() {...});

Answer 2

This section of the angular documentation explains what are the different ways of binding scope variables inside a directive to the parent scope.

What that code is doing is a two-way binding with the parent scope variable passed in stickyNote ondelete property