13.16 Comma Operator ( , )Syntax Expression[In, Yield, Await] : AssignmentExpression[?In, ?Yield, ?Await] Expression[?In, ?Yield, ?Await] , AssignmentExpression[?In, ?Yield, ?Await] 13.16.1 Runtime Semantics: Evaluation Expression : Expression , AssignmentExpression Let lref be ? Evaluation of Expression.Perform ? GetValue(lref).Let rref be ? Evaluation of AssignmentExpression.Return ? GetValue(rref). Note GetValue must be called even though its value is not used because it may have observable side-effects.