Found here: https://stackoverflow.com/questions/11604409/toggle-a-boolean-in-javascript

JS Toggle a Boolean variable.js

// ===========================================================
// Simple toggle
// ----------------------------------
var bool = true;
bool = !bool;

// ===========================================================
// Function to toggle
// ----------------------------------
$scope.form_state.showing = false;
$scope.toggle = function(){
  $scope.form_state.showing = !$scope.form_state.showing;
}

// ===========================================================
// Toggling capabilities wrapped into one little object
// ----------------------------------
$scope.form_state = {
  showing: false,
  show: function(){$scope.form_state.showing = true},
  hide: function(){$scope.form_state.showing = false},
  toggle: function(){
    $scope.form_state.showing = !$scope.form_state.showing;
  }
}

// usage
$scope.form_state.toggle();
$scope.form_state.hide();
$scope.form_state.show();