The union() method of Set instances takes a set and returns a new set containing elements which are in either or both of this set and the given set.| MDN Web Docs
Introduction This Ecma Standard defines the ECMAScript 2025 Language. It is the sixteenth edition of the ECMAScript Language Specification. Since publication of the first edition in 1997, ECMAScript has grown to be one of the world's most widely used general-purpose programming languages. It is| tc39.es