Check for NaN, null and >=0 in one condition

Question

I have a var a;

Its value can be NaN, null and any +ve/-ve number including 0.

I require a condition which filters out all the values of a such that

Answer 1

Ohk ...But i actually found the ans .. it is so Simple .

parseInt(null) = NaN.

So if(parseInt(a)>=0){} would do ...Yayyee