js中一些关于比较左右两边的值的题目

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);

答案：

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  

引：http://www.iteye.com/topic/903410