JavaScript: The Definitive Guide, Fourth Edition

Name

Number.NaN — the special not-a-number value

Availability

JavaScript 1.1; JScript 2.0, ECMAScript v1

Synopsis

Number.NaN

Description

Number.NaN is a special value that indicates that the result of some mathematical operation (such as taking the square root of a negative number) is not a number. parseInt( ) and parseFloat( ) return this value when they cannot parse the specified string, and you might use Number.NaN in a similar way to indicate an error condition for some function that normally returns a valid number.

JavaScript prints the Number.NaN value as NaN. Note that the NaN value always compares unequal to any other number, including NaN itself. Thus, you cannot check for the not-a-number value by comparing to Number.NaN. Use the isNaN( ) function instead. In ECMAScript v1 and later, you can also use the predefined global constant NaN instead of using Number.NaN.

See Also

isNaN( ), NaN