JScript ランゲージ リファレンス、isNaN メソッド
WScript.Echo(isNaN(1));
WScript.Echo(isNaN(1/0));
WScript.Echo(isNaN(0/0));
WScript.Echo(isNaN("foo"));
WScript.Echo(isNaN(1));
WScript.Echo(isNaN(1/0));
WScript.Echo(isNaN(0/0));
WScript.Echo(isNaN("foo"));