Found this way with IDENTITY and ALLOWIDENTITYINSERT=1

CREATE TABLE users (
	id identity NOT NULL,
	name VARCHAR(30) NOT NULL,
	PRIMARY KEY (id)
)
WITH %CLASSPARAMETER ALLOWIDENTITYINSERT = 1;

INSERT INTO users (id, name) VALUES (2, 'fred');
SELECT LAST_IDENTITY();

INSERT INTO users (name) VALUES ('ed');
SELECT LAST_IDENTITY();

Not sure if actually a good way to solve the issue

I see it in difficulty explaining of how to start using IRIS with NodeJS (actually with any supported language). It's not even simpler for NodeJS Developers who already familiar with IRIS and the complexity of getting drivers.

When on answer of how to start develop in NodeJS with IRIS, we could answer just install driver with npm and you are ready to go, then probably will be much more NodeJS based projects.