number vs finite

[bishopZ]

a quotation from underscore discussion:

_.isNumber( NaN ) is true because NaN is classified as a number just as
Infinity and -Infinity are.

The _.isNumber method is not intended for numeric validation just as _.isDate will not validate whether a date object is a valid date, new Date(Infinity).

If you're looking for validation there's _.isFinite or
ES6 Number.isFinite, Number.isNaN, Number.isInteger, and Number.isSafeInteger.