alert(typeof(NaN)); //number  

alert(typeof(Infinity));//number  

alert(typeof(null)  ); //object  

alert(typeof(undefined) ); //undefined  

alert((NaN==NaN) ); // false  

alert( (NaN!=NaN)  ); // true  

alert((NaN>NaN) );  //false  

alert((null==undefined) );  //true  

alert((null>=undefined));  //false  

alert((null<=undefined) );  //false  

alert((null==null));//true  

alert((null!=null) ); //false  

alert((null!=NaN) ); //true  

alert((null==NaN) );//fasle  

alert((NaN==undefined) ); //false  

alert((parseInt("123abc")));//123  

alert(("123abc"-0) ); //NaN  

alert((Infinity>10)); //true  

alert((Infinity>"abc")); //false  

alert((Infinity==NaN));//false  

alert((true==1) ); //true  

alert((new String("abc")=="abc")); //true  

alert((new String("abc")==="abc")); //false  

function step(a){  

   return function(x){  

      return x+a++;  

   }

}  

var a = step(10);  

var b = step(20);  

alert(a(10));//20  

alert(b(20));// 40  

var a="123abc";  

alert(typeof(a++));// number  

alert(a);//NaN