typescript double exclamation mark code example

Example 1: typescript double question mark

A = A ?? B;
//it is the same as
if( null != A )
    A = A;
else
    A = B;

Example 2: javascript operator double not

// convert to boolean 
// The following examples are the only values which result in a false expression

!!0 // false
!!"" // false
!!null // false
!!undefined // false
!!NaN // false