How to convert Cartesian2 to Cartesian3?

Sorry, may be this question so stupid, but I don't know how do this..

Well, a Cartesian2 is X/Y, while a Cartesian3 is X/Y/Z. So, I’d assume you can just do:

const ct3 = new Cartesian3(ct2.x, ct2.y); // params default to 0 if not supplied, so Z = 0