The Number.NaN static data property represents Not-A-Number, which is equivalent to NaN. For more information about the behaviors of NaN, see the description for the global property.
Value
The number value NaN.
Description
Because NaN is a static property of Number, you always use it as Number.NaN, rather than as a property of a number value.
Examples
Checking whether values are numeric
function sanitize(x) {
if (isNaN(x)) {
return Number.NaN;
}
return x;
}