How to recheck the input for condition

I have this code.

$scope.addingDirector = function(id, directorName){
    if(directorName){
        var find = _.filter($scope.directorArr, function(dir){
            //If required use .trim() like directorName.trim().toLowerCase() to strip whitespace
            return dir.toLowerCase() == directorName.toLowerCase();
        });
        if(find.length == 0){
            var titleDirector = {
                cpPortfolioItemId: id,
                name:directorName,
                job: 'director'
            };
            ContentAssessmentFactory.addDirectorName(titleDirector);
            $window.alert('Success!')
        }else{
            $window.alert('Director name already exist.');
        }
    }else{
        $window.alert('You cannot leave a field blank.');
    }
};

It checks the input box if there is an existing director name. If not it will add to the database. My problem is, when I click the submit button repeatedly it will add to the database repeatedly too. It will not recheck again the input box for every submit. Can someone help me here?

EDIT: When I close the modal, and then reopen and retype the same name it will prompt that it already exist.