JS加减乘除运算

//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(0.11).mul(0.5));  //输出：0.055