The following operations return NaN
The divisions 0/0, ∞/∞, ∞/−∞, −∞/∞, and −∞/−∞
The multiplications 0×∞ and 0×−∞
The power 1^∞
The additions ∞ + (−∞), (−∞) + ∞ and equivalent subtractions.
Real operations with complex results:
The square root of a negative number
The logarithm of a negative number
The tangent of an odd multiple of 90 degrees (or π/2 radians)
The inverse sine or cosine of a number which is less than −1 or greater than +1.
The following operations return values for numeric operations. Hence typeof Nan is a number. NaN is an undefined number in mathematical terms. ∞ + (-∞) is not equal to ∞ + (-∞). But we get that NaN is typeof number because it results from a numeric operation.
From wiki:
