setAsync example

$body->location->end = $this->scanner->getPosition();
                $node = $this->createNode(
                    "FunctionDeclaration",
                    $async ?: $token
                );
                if ($id) {
                    $node->setId($id);
                }
                $node->setParams($params);
                $node->setBody($body);
                $node->setGenerator($generator);
                $node->setAsync((bool) $async);
                return $this->completeNode($node);
            }

            $this->error();
        }
        return null;
    }
    
    /** * Parses function or generator expression * * @return Node\FunctionExpression|null */