A series of methods that can be strung together to automate data import through Import Sets

createDataSource.js

// @param att {GlideRecord - sys_attachment}
function createDataSource(att) {
	// Create new data source
	var ds = new GlideRecord("sys_data_source");
	ds.initialize();
	ds.setValue("name", att.getValue("file_name"));
	ds.setValue("import_set_table_name", "x_nuvo_eam_pi_device_import");
	ds.setValue("type", "File");
	ds.setValue("format", "CSV");
	ds.setValue("file_retrieval_method", "Attachment");
	ds.setValue("file_path", att.getValue("file_name"));
	var newDataSource = ds.insert();

	// Copy project attachment to data source
	var ga = new GlideSysAttachment();
	ga.copy(att.getValue("table_name"),
			att.getValue("table_sys_id"),
			'sys_data_source', 
			newDataSource);

	loadDataSource(newDataSource);
	return newDataSource;

}

loadDataSource.js

function loadDataSource(datasource_sysid) {
  var ds = new GlideRecord("sys_data_source");
  ds.get(datasource_sysid);
  var redirectStr = "sys_import.do?";
  redirectStr += "import_source=data_source";
  redirectStr += "&sysparm_data_source=" + ds.getUniqueValue();
  redirectStr += "&sysparm_tablename=" + ds.getValue("import_set_table_name"); 
  redirectStr += "&sysparm_recreate_table=false"; 
  redirectStr += "&sysparm_tablelabel=" + encodeURIComponent(ds.getValue("name"));
  redirectStr += "&create_new_module=ON";
  redirectStr += "&sysparm_extends=sys_import_set_row";
  redirectStr += "&selected_application=import_sets";

  var resourceBase = gs.getProperty('glide.servlet.uri');

  var sm = new sn_ws.RESTMessageV2();
  var resource = resourceBase + redirectStr;

  sm.setHttpMethod("get");
  sm.setEndpoint(resource);

  try {	
    var userId = ""; // SYSTEM IMPORT USER WITH ADMIN CREDENTIAL
    var pwd = ""; // SYSTEM IMPORT USER WITH ADMIN CREDENTIAL
    sm.setBasicAuth(userId,pwd);

    var response = sm.execute();
    var status_code = response.getStatusCode();
    if (!status_code.toString().startsWith("20")) {
      gs.error("Import failed with error code " + status_code);
      return; 
    }
  } catch(er) {
    gs.error("Import failed with error " + er.getMessage());
    return;
  }
}

Note: The method described here utilizes undocumented features of ServiceNow which may or may not be supported across upgrades. These methods are inspired by the OOB UI Actions used to use OOB Import Set functionality

Scripts above can be used to copy a CSV file to a data source, then import that data source into an Import Set.

Once an import set is created with data from the CSV, the GlideImportSetTransformerWorker class can be used to import data using transform maps without user interaction.

Further implementation steps are left to the developer to handle multiple transform maps, handling of errors and other issues that may arise.