Edit in JSFiddle

function isStrictNaN(x) {
    if(x !== x) {
        $("body").append(x + ' is NaN!!!');
    }
    else {
        $("body").append(x + ' is not NaN');
    }
    $("body").append('<br>');
}
isStrictNaN(1);
isStrictNaN(0);
isStrictNaN(undefined);
isStrictNaN([7]);
isStrictNaN({});
isStrictNaN();
isStrictNaN("str");
isStrictNaN({foo: "bar"});
isStrictNaN(NaN);