$tv = $modx->getObject('modTemplateVar', array('name' => 'hitcount'));

$criteria = array(
		'tmplvarid' => $tv->get('id'),
		'contentid' => $modx->resourceIdentifier
);

if(!$tvResource = $modx->getObject('modTemplateVarResource', $criteria)){
	$tvResource = $modx->newObject('modTemplateVarResource');
	$tvResource->set('value', 1);
	$tvResource->set('tmplvarid', $tv->get('id'));
	$tvResource->set('contentid', $modx->resourceIdentifier);
	$tvResource->save();
} else {
	$value = (int)$tvResource->get('value') + 1;
	$tvResource->set('value', $value);
	$tvResource->save();
}