Assuming you add a validation class via the frontend_class let’s say “validate-custom-class” you’ll need to use the following JS to add a custom validation based on a this class:
require([
'jquery',
'jquery/ui',
'jquery/validate',
'mage/translate'
], function($){
$.validator.addMethod('validate-custom-class', function (value) {
// Add your validation logic here
// Needs to return true if validation pass
// Or false if validation fails
}, $.mage.__('Field is not valid'));
});