valueOf() toString()

转帖：http://www.xiaoxiaozi.com/2010/02/21/1706/

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。

• toString()——返回对象的原始字符串表示
• valueOf()——返回最适合该对象的原始值

<script type="text/javascript">
function Money(gold, silver, coin)
{
this.gold = gold;
this.silver = silver;
this.coin = coin;
}

Money.parse = function(value)
{
var coin = parseInt(value % 25);
var silver = parseInt(value / 25 % 20);
var gold = parseInt(value / 500);
return new Money(gold, silver, coin);
}

Money.prototype.valueOf = function()
{
return ((this.gold * 20) + this.silver) * 25 + this.coin;
}

Money.prototype.toString = function()
{
return this.gold + "两黄金，" + this.silver + " 两白银，" + this.coin + "文钱";
}

var money1 = new Money(5, 6, 1);  
var money2 = new Money(2, 4, 6);  
//money1 + money2 调用两者valueOf之后的值相加
var money3 = Money.parse(money1 + money2);
//打印时调用了 toString方法
alert(money3);
</script>