You can use the RESTMessageV2() constructor with no parameters to define a REST message entirely in the script.

When using this constructor you must provide an endpoint and HTTP method. In this example, the script creates an empty REST message and sets the values needed to insert an incident record.

var restMessage = new sn_ws.RESTMessageV2();
restMessage.setBasicAuth("admin", "admin");
restMessage.setHttpMethod("post");
restMessage.setEndpoint("http://<instance>.service-now.com/api/now/table/incident");
restMessage.setRequestBody("{\"short_description\" : \"Test incident\"}");
var response = restMessage.execute();