typescript double question mark

1//Similar to || but only returns the right-hand operand if the left-hand is null or undefined
20 ?? "other" // 0
3false ?? "other" // false
4null ?? "other" // "other"
5undefined ?? "other" // "other"

1A = A ?? B;
2//it is the same as
3if( null != A )
4    A = A;
5else
6    A = B;