Error: $digest already in progress

Duplicated: Prevent error $digest already in progress when calling $scope.$apply()

That error you are getting means Angular’s dirty checking is already in progress.

Most recent best practices say that we should use $timeout if we want to execute any code in the next digest iteration:

$timeout(function() {
  // the code you want to run in the next digest
});

Previous response: (don’t use this approach)

Use a safe apply, like this:

$rootScope.$$phase || $rootScope.$apply();

Why don’t you invert the condition?

$scope.$on('$locationChangeStart', function (event, next, current) {                
    if (confirm("Are you sure you want to leave this page?")) {
        event.preventDefault();
    }
});