Number.prototype add + sub + mul + div

Number.js

//addition 
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  
}  
  
//substruction
Number.prototype.sub = function (arg){  
    return this.add(-arg);  
}  
  
//multiplication
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)  
}  
  
//division
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);  
    }  
}