很有意思的js考试题目

alert(typeof(NaN));     alert(typeof(Infinity));    alert(typeof(null));     alert(typeof(undefined));     alert(NaN==NaN);     alert(NaN!=NaN);     alert(NaN>NaN);      alert(null==undefined);      alert(null>=undefined);      alert(null<=undefined);      alert(null==null);    alert(null!=null);     alert(null!=NaN);     alert(null==NaN);    alert(NaN==undefined);     alert(parseInt("123abc"));    alert("123abc"-0);     alert(Infinity>10);     alert(Infinity>"abc");     alert(Infinity==NaN);    alert(true==1);     alert(new String("abc")=="abc");     alert(new String("abc")==="abc");        function step(a){       return function(x){          return x+a++;       }    }    var a = step(10);    var b = step(20);    alert(a(10));    alert(b(20));    var a="123abc";    alert(typeof(a++));    alert(a);