The so called 2-way binding in AngularJS. More like lol-binding imo.

my-directive.js

angular.directive( 'myDirective', function () {
  return {
    link: function ( scope, element ) {
      element.on( 'click', function ( event ) {
        scope.foo = 'bar';
        // need to $scope.$apply here. Ugly! Should be automagic.
      } );
    },
    restrict: 'E'
  };
} );

view.ng.html

<div my-directive></div>