ValidationController.cls

public with sharing class ValidationController {
    @AuraEnabled
    public static ValidationResult validateData(String name, String email, Integer age) {
        ValidationResult result = new ValidationResult();
        if (name == null || name.isEmpty()) {
            result.addError('Name is required');
        }
        if (email == null || email.isEmpty() || !email.contains('@')) {
            result.addError('Valid email is required');
        }
        if (age == null || age < 18) {
            result.addError('Age must be 18 or older');
        }
        return result;
    }

    public class ValidationResult {
        @AuraEnabled
        public List<String> errors { get; set; }

        public ValidationResult() {
            errors = new List<String>();
        }

        public void addError(String error) {
            errors.add(error);
        }
    }
}