A null value represents nothing, nonexistent or invalid object or address. It converts to
0 in simple arithmetic operations and it’s global object.
null == false gives us false.
The global undefined property represents the primitive value
undefined. It tells us something has not assigned value; isn’t defined. undefined isn’t converted into any number, so using it in maths calculations returns
NaN (Not-A-Number) represents something which is not a number, even though it’s actually a number. It’s not equal to itself and to check if something is NaN we need to use isNaN() function.