基本上，所有JS数据类型都拥有valueOf和toString这两个方法，null除外。它们俩解决javascript值运算与显示的问题。
1.用法如下：
toString()方法：返回对象的字符串表示。
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ottom: silver 1px solid; border-left: silver 1px solid; padding-bottom: 3px; padding-left: 3px; padding-right: 3px; border-collapse: collapse; border-top: silver 1px solid; border-right: silver 1px solid; padding-top: 3px">对象
| ottom: silver 1px solid; border-left: silver 1px solid; padding-bottom: 3px; padding-left: 3px; padding-right: 3px; border-collapse: collapse; border-top: silver 1px solid; border-right: silver 1px solid; padding-top: 3px">操作 |
ottom: silver 1px solid; border-left: silver 1px solid; padding-bottom: 3px; line-height: 1.5; padding-left: 3px; padding-right: 3px; border-collapse: collapse; font-family: Verdana,Arial; color: rgb(48,48); font-size: 12px; word-break: break-all; border-top: silver 1px solid; border-right: silver 1px solid; padding-top: 3px">Arrayottom: silver 1px solid; border-left: silver 1px solid; padding-bottom: 3px; line-height: 1.5; padding-left: 3px; padding-right: 3px; border-collapse: collapse; font-family: Verdana,48); font-size: 12px; word-break: break-all; border-top: silver 1px solid; border-right: silver 1px solid; padding-top: 3px">将Array
的元素转换为字符串。结果字符串由逗号分隔，且连接起来。ottom: silver 1px solid; border-left: silver 1px solid; padding-bottom: 3px; line-height: 1.5; padding-left: 3px; padding-right: 3px; border-collapse: collapse; font-family: Verdana,48); font-size: 12px; word-break: break-all; border-top: silver 1px solid; border-right: silver 1px solid; padding-top: 3px">Booleanottom: silver 1px solid; border-left: silver 1px solid; padding-bottom: 3px; line-height: 1.5; padding-left: 3px; padding-right: 3px; border-collapse: collapse; font-family: Verdana,48); font-size: 12px; word-break: break-all; border-top: silver 1px solid; border-right: silver 1px solid; padding-top: 3px">如果 Boolean 值是true
，则返回 “true”。否则，返回 “false”。ottom: silver 1px solid; border-left: silver 1px solid; padding-bottom: 3px; line-height: 1.5; padding-left: 3px; padding-right: 3px; border-collapse: collapse; font-family: Verdana,48); font-size: 12px; word-break: break-all; border-top: silver 1px solid; border-right: silver 1px solid; padding-top: 3px">Dateottom: silver 1px solid; border-left: silver 1px solid; padding-bottom: 3px; line-height: 1.5; padding-left: 3px; padding-right: 3px; border-collapse: collapse; font-family: Verdana,48); font-size: 12px; word-break: break-all; border-top: silver 1px solid; border-right: silver 1px solid; padding-top: 3px">返回日期的文字表示法。ottom: silver 1px solid; border-left: silver 1px solid; padding-bottom: 3px; line-height: 1.5; padding-left: 3px; padding-right: 3px; border-collapse: collapse; font-family: Verdana,48); font-size: 12px; word-break: break-all; border-top: silver 1px solid; border-right: silver 1px solid; padding-top: 3px">Errorottom: silver 1px solid; border-left: silver 1px solid; padding-bottom: 3px; line-height: 1.5; padding-left: 3px; padding-right: 3px; border-collapse: collapse; font-family: Verdana,48); font-size: 12px; word-break: break-all; border-top: silver 1px solid; border-right: silver 1px solid; padding-top: 3px">返回一个包含相关错误消息的字符串。ottom: silver 1px solid; border-left: silver 1px solid; padding-bottom: 3px; line-height: 1.5; padding-left: 3px; padding-right: 3px; border-collapse: collapse; font-family: Verdana,48); font-size: 12px; word-break: break-all; border-top: silver 1px solid; border-right: silver 1px solid; padding-top: 3px">Functionottom: silver 1px solid; border-left: silver 1px solid; padding-bottom: 3px; line-height: 1.5; padding-left: 3px; padding-right: 3px; border-collapse: collapse; font-family: Verdana,48); font-size: 12px; word-break: break-all; border-top: silver 1px solid; border-right: silver 1px solid; padding-top: 3px">返回如下格式的字符串，其中functionname是被调用toString
方法函数的名称：
ottom: 0px">function functionname( ) { [native code] }
ottom: silver 1px solid; border-left: silver 1px solid; padding-bottom: 3px; line-height: 1.5; padding-left: 3px; padding-right: 3px; border-collapse: collapse; font-family: Verdana,48); font-size: 12px; word-break: break-all; border-top: silver 1px solid; border-right: silver 1px solid; padding-top: 3px">Numberottom: silver 1px solid; border-left: silver 1px solid; padding-bottom: 3px; line-height: 1.5; padding-left: 3px; padding-right: 3px; border-collapse: collapse; font-family: Verdana,48); font-size: 12px; word-break: break-all; border-top: silver 1px solid; border-right: silver 1px solid; padding-top: 3px">返回数字的文字表示。ottom: silver 1px solid; border-left: silver 1px solid; padding-bottom: 3px; line-height: 1.5; padding-left: 3px; padding-right: 3px; border-collapse: collapse; font-family: Verdana,48); font-size: 12px; word-break: break-all; border-top: silver 1px solid; border-right: silver 1px solid; padding-top: 3px">Stringottom: silver 1px solid; border-left: silver 1px solid; padding-bottom: 3px; line-height: 1.5; padding-left: 3px; padding-right: 3px; border-collapse: collapse; font-family: Verdana,48); font-size: 12px; word-break: break-all; border-top: silver 1px solid; border-right: silver 1px solid; padding-top: 3px">返回String
对象的值。ottom: silver 1px solid; border-left: silver 1px solid; padding-bottom: 3px; line-height: 1.5; padding-left: 3px; padding-right: 3px; border-collapse: collapse; font-family: Verdana,48); font-size: 12px; word-break: break-all; border-top: silver 1px solid; border-right: silver 1px solid; padding-top: 3px">默认ottom: silver 1px solid; border-left: silver 1px solid; padding-bottom: 3px; line-height: 1.5; padding-left: 3px; padding-right: 3px; border-collapse: collapse; font-family: Verdana,48); font-size: 12px; word-break: break-all; border-top: silver 1px solid; border-right: silver 1px solid; padding-top: 3px">返回 “imsun">[object objectname]”，其中imsun">objectname是对象类型的名称。
valueOf()方法：返回指定对象的原始值。
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ottom: silver 1px solid; border-left: silver 1px solid; padding-bottom: 3px; padding-left: 3px; padding-right: 3px; border-collapse: collapse; border-top: silver 1px solid; border-right: silver 1px solid; padding-top: 3px">对象
| ottom: silver 1px solid; border-left: silver 1px solid; padding-bottom: 3px; padding-left: 3px; padding-right: 3px; border-collapse: collapse; border-top: silver 1px solid; border-right: silver 1px solid; padding-top: 3px">返回值 |
ottom: silver 1px solid; border-left: silver 1px solid; padding-bottom: 3px; line-height: 1.5; padding-left: 3px; padding-right: 3px; border-collapse: collapse; font-family: Verdana,48); font-size: 12px; word-break: break-all; border-top: silver 1px solid; border-right: silver 1px solid; padding-top: 3px">Arrayottom: silver 1px solid; border-left: silver 1px solid; padding-bottom: 3px; line-height: 1.5; padding-left: 3px; padding-right: 3px; border-collapse: collapse; font-family: Verdana,48); font-size: 12px; word-break: break-all; border-top: silver 1px solid; border-right: silver 1px solid; padding-top: 3px">数组的元素被转换为字符串，这些字符串由逗号分隔，连接在一起。其操作与Array.toString
和Array.join
方法相同。ottom: silver 1px solid; border-left: silver 1px solid; padding-bottom: 3px; line-height: 1.5; padding-left: 3px; padding-right: 3px; border-collapse: collapse; font-family: Verdana,48); font-size: 12px; word-break: break-all; border-top: silver 1px solid; border-right: silver 1px solid; padding-top: 3px">Booleanottom: silver 1px solid; border-left: silver 1px solid; padding-bottom: 3px; line-height: 1.5; padding-left: 3px; padding-right: 3px; border-collapse: collapse; font-family: Verdana,48); font-size: 12px; word-break: break-all; border-top: silver 1px solid; border-right: silver 1px solid; padding-top: 3px">Boolean 值。ottom: silver 1px solid; border-left: silver 1px solid; padding-bottom: 3px; line-height: 1.5; padding-left: 3px; padding-right: 3px; border-collapse: collapse; font-family: Verdana,48); font-size: 12px; word-break: break-all; border-top: silver 1px solid; border-right: silver 1px solid; padding-top: 3px">Dateottom: silver 1px solid; border-left: silver 1px solid; padding-bottom: 3px; line-height: 1.5; padding-left: 3px; padding-right: 3px; border-collapse: collapse; font-family: Verdana,48); font-size: 12px; word-break: break-all; border-top: silver 1px solid; border-right: silver 1px solid; padding-top: 3px">存储的时间是从 1970 年 1 月 1 日午夜开始计的毫秒数decoration: none" href="http://blog.sina.com.cn/s/glossary.htm#defutctime">UTC。ottom: silver 1px solid; border-left: silver 1px solid; padding-bottom: 3px; line-height: 1.5; padding-left: 3px; padding-right: 3px; border-collapse: collapse; font-family: Verdana,48); font-size: 12px; word-break: break-all; border-top: silver 1px solid; border-right: silver 1px solid; padding-top: 3px">Functionottom: silver 1px solid; border-left: silver 1px solid; padding-bottom: 3px; line-height: 1.5; padding-left: 3px; padding-right: 3px; border-collapse: collapse; font-family: Verdana,48); font-size: 12px; word-break: break-all; border-top: silver 1px solid; border-right: silver 1px solid; padding-top: 3px">函数本身。ottom: silver 1px solid; border-left: silver 1px solid; padding-bottom: 3px; line-height: 1.5; padding-left: 3px; padding-right: 3px; border-collapse: collapse; font-family: Verdana,48); font-size: 12px; word-break: break-all; border-top: silver 1px solid; border-right: silver 1px solid; padding-top: 3px">Numberottom: silver 1px solid; border-left: silver 1px solid; padding-bottom: 3px; line-height: 1.5; padding-left: 3px; padding-right: 3px; border-collapse: collapse; font-family: Verdana,48); font-size: 12px; word-break: break-all; border-top: silver 1px solid; border-right: silver 1px solid; padding-top: 3px">数字值。ottom: silver 1px solid; border-left: silver 1px solid; padding-bottom: 3px; line-height: 1.5; padding-left: 3px; padding-right: 3px; border-collapse: collapse; font-family: Verdana,48); font-size: 12px; word-break: break-all; border-top: silver 1px solid; border-right: silver 1px solid; padding-top: 3px">Objectottom: silver 1px solid; border-left: silver 1px solid; padding-bottom: 3px; line-height: 1.5; padding-left: 3px; padding-right: 3px; border-collapse: collapse; font-family: Verdana,48); font-size: 12px; word-break: break-all; border-top: silver 1px solid; border-right: silver 1px solid; padding-top: 3px">对象本身。这是默认情况。ottom: silver 1px solid; border-left: silver 1px solid; padding-bottom: 3px; line-height: 1.5; padding-left: 3px; padding-right: 3px; border-collapse: collapse; font-family: Verdana,48); font-size: 12px; word-break: break-all; border-top: silver 1px solid; border-right: silver 1px solid; padding-top: 3px">Stringottom: silver 1px solid; border-left: silver 1px solid; padding-bottom: 3px; line-height: 1.5; padding-left: 3px; padding-right: 3px; border-collapse: collapse; font-family: Verdana,48); font-size: 12px; word-break: break-all; border-top: silver 1px solid; border-right: silver 1px solid; padding-top: 3px">字符串值。
2.两者的共同点与不同点：
共同点：在 JavaScript 中，toString()方法和valueOf()方法，在输出对象时会自动调用。
不同点：二者并存的情况下，在数值运算中，优先调用了valueOf，字符串运算中，优先调用了toString。
例子1如下：
rush:js;">
例子2如下：
rush:js;">
function obj()
{ }
obj.prototype.toString = function(){
return 'dfsf';
};
obj.prototype.valueOf = function(){
return '3333';
};
var e = new obj();
var o = new obj();
alert(o);//alert(obj.toString())
alert(o+e);//alert(obj.valueOf()+obj.valueOf())
****toString vs valueOf的差别:
返回值类型的差别：
1. toString一定将所有内容转为字符串
2. valueOf取出对象内部的值，不进行类型转换
用途的差别：
1. valueOf专用于算数计算和关系运算
2. toString专用于输出字符串
共同的缺点：无法获取null和undefined的值
PS：Java中parse（）和valueOf（），toString（）的区别
1.parse()是SimpleDateFomat里面的方法，你说的应该是parseInt()或parsefloat()这种方法吧，
顾名思义 比如说parseInt()就是把String类型转化为int类型。
如
String a= "123";
int b = Integer.parseInt(a);
这样b就等于123了。
2.ValueOf()方法比如说 Integer.valueOf() 是把String类型转化为Integer类型(注意：是Integer类型，而不是int类型，int类型是表示数字的简单类型，Integer类型是一个引用的复杂类型)
如：
rush:js;">
String a= "123";
Integer c =Integer.valueOf(a);
//Integer类型可以用intValue
方法转化为int类型
int b =c.intValue();
这时候这个b就等于123了
3. toString()可以把一个引用类型转化为String字符串类型。
下面举个例子与2相反，把Integer转化为String类型：
Integer a = new Integer(123);
String b =a.toString();
这时候b就是 "123" 了
int
parseInt()
String intValue()
ValueOf()
Integer
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