validateStartsWith function

String? Function(dynamic) validateStartsWith({
  1. required String prefix,
  2. String? failMessage,
})

Returns error message if doesn't start with prefix, null if valid

Implementation

String? Function(dynamic) validateStartsWith({
  required String prefix,
  String? failMessage,
}) {
  return (dynamic value) {
    if (!isStartsWith(value, prefix)) {
      return failMessage ?? 'This field must start with "$prefix"';
    }
    return null;
  };
}