alert(typeof(1)); // number alert(typeof(NaN)); // number alert(typeof(Number.MIN_VALUE)); // number alert(typeof(Infinity)); // number alert(typeof("123")); // string alert(typeof(true)); // boolean alert(typeof(window)); // object alert(typeof(document)); // object alert(typeof(null)); // object alert(typeof(eval)); // function alert(typeof(Date)); // function alert(typeof(sss)); // undefined alert(typeof(undefined)); // undefined