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>