一,对于引用类型对象(我指的是String,Date,Object,Array,Function,Boolean)的+运算符运算过程如下!

1,首先调用此对象的valueOf方法,得到返回数值A

2,然后把此数值A转换成数字,得到的是最终数值

我的测试如下:

复制代码 代码如下:

function w(s){

document.writeln("<br/>");

document.writeln(s);

document.writeln("<br/>-----------------------------");

}

String.prototype.valueOf=function(){return 1;};

w(+new String("sss"));//输出1

String.prototype.valueOf=function(){return "a";};

w(+new String("sss"));//输出NaN

Date.prototype.valueOf=function(){return 1;};

w(+new Date());//输出1

Date.prototype.valueOf=function(){return "a";};

w(+new Date());//输出NaN

Object.prototype.valueOf=function(){return 1;};

w(+{});//输出1

Object.prototype.valueOf=function(){return "a";};

w(+{});//输出NaN

Array.prototype.valueOf=function(){return 1;};

w(+[]);//输出1

Array.prototype.valueOf=function(){return "a";};

w(+[]);//输出NaN

var s=function(){};

Function.prototype.valueOf=function(){return 1;};

w(+s);//输出1

Function.prototype.valueOf=function(){return "a";};

w(+s);//输出NaN

Boolean.prototype.valueOf=function(){return 1;};

w(+new Boolean());//输出1

Boolean.prototype.valueOf=function(){return "a";};

w(+new Boolean());//输出NaN

二,对于基本数据数据类型,其值转换成数字

复制代码 代码如下:

w(+5);//输出5

w(+true);//输出1

w(+false);//输出0

w(+"ss");//输出NaN

w(+"111");//输出111