Converts Object to boolean. If it was falsey (e.g. 0, null, undefined, etc.), it will be false, otherwise, true.
!oObject // inverted boolean
!!oObject // non inverted boolean so true boolean representation
So !! is not an operator, it's just the ! operator twice.
It returns the right operand (rightExpression) if the left operand (leftExpression) is null or undefined.