function isnan( value ) {
	return (
		isNumber( value ) &&
		isNan( value.valueOf() )
	);
}
Tests if a value is a number object having a value of `NaN`.

@param {*} value - value to test
@returns {boolean} boolean indicating if a value is a number object having a value of `NaN`

@example
var bool = isnan( NaN );
// returns false

@example
var bool = isnan( new Number( NaN ) );
// returns true