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

typeof x == "number" && x >= 0

This works as follows:

• null -- typeof null == "object" so first part of expression returns false
• NaN -- typeof NaN == "number" but NaN is not greater than, less than or equal to any number including itself so second part of expression returns false
• number -- any other number greater than or equal to zero the expression returns true