function w(s){
document.writeln("<br/>");
document.writeln(s);
document.writeln("<br/>-----------------------------");
}
String.prototype.valueOf=function(){return 1;};
w(+new String("sss"));//輸出1
String.prototype.valueOf=function(){return "a";};
w(+new String("sss"));//輸出NaN


Date.prototype.valueOf=function(){return 1;};
w(+new Date());//輸出1
Date.prototype.valueOf=function(){return "a";};
w(+new Date());//輸出NaN

Object.prototype.valueOf=function(){return 1;};
w(+{});//輸出1
Object.prototype.valueOf=function(){return "a";};
w(+{});//輸出NaN

Array.prototype.valueOf=function(){return 1;};
w(+[]);//輸出1
Array.prototype.valueOf=function(){return "a";};
w(+[]);//輸出NaN

var s=function(){};
Function.prototype.valueOf=function(){return 1;};
w(+s);//輸出1
Function.prototype.valueOf=function(){return "a";};
w(+s);//輸出NaN

Boolean.prototype.valueOf=function(){return 1;};
w(+new Boolean());//輸出1
Boolean.prototype.valueOf=function(){return "a";};
w(+new Boolean());//輸出NaN

w(+5);//輸出5
w(+true);//輸出1
w(+false);//輸出0
w(+"ss");//輸出NaN
w(+"111");//輸出111