Given this FileValidationPipe code snippet, what happens if a user uploads a file with an unsupported extension?

Given this FileValidationPipe code snippet, what happens if a user uploads a file with an unsupported extension?

class FileValidationPipe implements PipeTransform {
  transform(file) {
    const allowed = ['jpg', 'png'];
    const ext = file.originalname.split('.').pop();
    if (!allowed.includes(ext)) {
      throw new BadRequestException('Invalid file type');
    }
    return file;
  }
}