In ECMAScript, NaN is classified as a primitive value.
NaN means "Not-a-Number". It is used to signify that a value
is not a legal number.
Note that the primitive value, Infinity,
is used to signify that a number, 1.5x10321 for example,
has exceeded the defined range of legal values for a floating point
You can use the isNan function to
test a value to see if it is a NaN.