JS之小数精度问题

<script type="text/javascript" language="javascript">
//加法
Number.prototype.add = function(arg){
var r1,r2,m;
try{r1=this.toString().split(".")[1].length}catch(e){r1=0}
try{r2=arg.toString().split(".")[1].length}catch(e){r2=0}
m=Math.pow(10,Math.max(r1,r2))
return (this*m+arg*m)/m;
}

//减法
Number.prototype.sub = function (arg){
return this.add(-arg);
}

//乘法
Number.prototype.mul = function (arg)
{
var m=0,s1=this.toString(),s2=arg.toString();
try{m+=s1.split(".")[1].length}catch(e){}
try{m+=s2.split(".")[1].length}catch(e){}
return Number(s1.replace(".",""))*Number(s2.replace(".",""))/Math.pow(10,m);
}

//除法
Number.prototype.div = function (arg){
var t1=0,t2=0,r1,r2;
try{t1=this.toString().split(".")[1].length}catch(e){}
try{t2=arg.toString().split(".")[1].length}catch(e){}
with(Math){
r1=Number(this.toString().replace(".",""))
r2=Number(arg.toString().replace(".",""))
return (r1/r2)*pow(10,t2-t1);
}
}
//测试
alert(Number(0.09999999).add(0.00000001));//弹出: 0.1
//注意，如果是负数，一定要先使用Number转型，否则结果不正确
alert(Number(-0.09999999).sub(0.00000001));//弹出: -0.1
alert(Number(0.012345).mul(0.000001));//弹出: 1.2345e-8
alert(Number(0.000001).div(0.0001));//弹出: 0.01
</script>